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RAADSMA, H. W., G. D. GRAY e R. R. WOOLASTON. "Breeding for disease resistance in Merino sheep in Australia". Revue Scientifique et Technique de l'OIE 17, n. 1 (1 aprile 1998): 315–28. http://dx.doi.org/10.20506/rst.17.1.1103.
Testo completo
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Cottle, D. J., M. T. Harrison e A. Ghahramani. "Sheep greenhouse gas emission intensities under different management practices, climate zones and enterprise types". Animal Production Science 56, n. 3 (2016): 507. http://dx.doi.org/10.1071/an15327.
Testo completoAbstract (sommario):
Greenhouse gas emissions (GHG) from broadacre sheep farms constitute ~16% of Australia’s total livestock emissions. To study the diversity of Australian sheep farming enterprises a combination of modelling packages was used to calculate GHG emissions from three sheep enterprises (Merino ewe production for wool and meat, Merino-cross ewes with an emphasis on lamb production, and Merino wethers for fine wool production) at 28 sites across eight climate zones in southern Australia. GHG emissions per ha, per dry sheep equivalents and emissions intensity (EI) per tonne of clean wool or liveweight sold under different pasture management or animal breeding options (that had been previously determined in interviews with farmers) were assessed relative to baseline farms in each zone (‘Nil’ option). Increasing soil phosphorus fertility or sowing 40% of the farm area to lucerne resulted in the smallest and largest changes in GHG/dry sheep equivalents, respectively (–66%, 113%), though both of these options had little influence on EI for either clean wool or liveweight sold. Breeding ewes with greater body size or genotypes with higher fleece weight resulted in 11% and 9% reductions, respectively, in EI. Enterprises specialising in lamb production (crossbred ewes) had 89% lower EI than enterprises specialising in fine wool production (Merino wethers). Thus, sheep producers aiming for lower EI could focus more on liveweight turnoff than wool production. Emissions intensities were typically highest in cool temperate regions with high rainfall and lowest in semiarid and arid regions with low aboveground net primary productivity. Overall, animal breeding options reduced EI more than feedbase interventions.
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Lakota, E. А. "PRESERVATION OF GENETIC POTENTIAL OF STAVROPOL SHEEP BREED FOR POVOLZHYE DREY STEPPE ZONE". Vestnik of Ulyanovsk state agricultural academy, n. 3(50) (8 settembre 2020): 179–84. http://dx.doi.org/10.18286/1816-4501-2020-3-179-184.
Testo completoAbstract (sommario):
In conditions of Povolzhye steppe zone development of productive qualities of Stavropol breed sheep was conducted by meat merino sheep. Experimental research was carried out in ZAO «Novaya Zhizn» in Novouzensky district of Saratov region, located in semi desert zone, bordering upon South-West Khazakhstan. The research aim was the increase and maintenance of genetic potential of Stavropol breed sheep of Povolzhye population. Working procedure is based on guidelines of the All-Union Academy of Agricultural sciences, All Union research institute of sheep and goat breeding. The study materials were Stavropol pure breed sheep and 1/8 –thoroughbred cross breed with Australian meat merino herdmates. As the result of stepped breeding of local Stavropol ewe with half bred by Australian meat merino ram- breeder of Stavropol breed animals of 1/2 ,1/4, 1/8 –blood were obtained, which then one- shear tupped by breeding «inter se». It is proved that in applying such selective method 1/8-blood by Australian meat merino sheep were characterized with higher body weight, better wool quality in contrast to Stavropol pure –breed herdmates. So, in 1/8-blood by Australian meat merino of hybrid ewe during breeding «inter se» live body at birth was higher than at pure breed herdmates for 5,56 %, during ablactation –at the age of 4 months - for 6,38 % (difference isn’t accurate). According to sharing of wool in grease, superiority of ewe of hybrid origin over pure breed was 5,6 % (Р≥0,99), but in terms of washed fiber it increases to 8,3 % (Р≥0,999). So, in dry steppe zone of Povolzhye new improved, according to its productive qualities, genotype of Stavropol breed sheep is created with retention of genetic resource that is essential economic factor for the modern maintenance of fine-wool sheep breeding field.
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Wilkes, M. J., P. I. Hynd e W. S. Pitchford. "Damara sheep have higher digestible energy intake than Merino sheep when fed low-quality or high-quality feed". Animal Production Science 52, n. 1 (2012): 30. http://dx.doi.org/10.1071/an11033.
Testo completoAbstract (sommario):
The use of animals that are resilient to challenging environments is becoming of increasing importance in animal production systems. Interest in breeds of sheep such as the Damara for sheep meat production is increasing in Australia. Anecdotally this breed outperforms the traditionally grazed Merino in the harsh rangeland environments encountered in the Pastoral Zone of Australia, but little evidence is available to support this claim. A trial was conducted to quantify differences in the efficiency of feed utilisation and growth performance of Damara and Merino sheep under two contrasting dietary regimes. Eighteen castrate males of each breed were offered a ‘low-quality’ diet (L) (7 MJ/kg ME; 8% crude protein, as per manufacturer’s analysis) followed by a ‘high-quality’ diet (H) (11 MJ/kg dry matter and 16% crude protein, as per manufacturer’s analysis). On the L diet, Damaras had similar ad libitum feed intake as Merinos, but the digestibility of feed dry matter and energy was ~10% higher in Damaras than Merinos. Damaras also gained weight (38 g/day) on the L diet, while Merinos lost weight (28 g/day) (P < 0.002). On the H diet the Damaras consumed 14% more feed (P < 0.053) and grew 30% faster than Merinos (P < 0.002), but there was no difference in the apparent dry matter or energy digestibility of the feed. At the conclusion of the trial the Damara carcasses were 22% heavier (28.1 versus 23.1 kg), and had higher dressing percentages (53.2 versus 41.5%) than Merinos, but the proportions of carcass components did not differ. The Damaras achieved higher total digestible energy intakes than the Merinos on both diets. On the low-quality feed this was achieved through higher feed digestibility and on the high-quality feed through greater voluntary feed intake. We speculate that this arises from variation between the breeds in rumen volume, particle flow and the site of digestion, but further studies are required to confirm this contention. The ability of Damara sheep to obtain more nutrients from widely differing feed bases makes them an attractive alternative sheep breed for sheep meat production. Furthermore, the presence of such variation between genotypes offers potential for selective breeding and development of commercial lines of sheep.
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Williams, A. R., L. J. E. Karlsson, D. G. Palmer, P. E. Vercoe, I. H. Williams, J. C. Greeff e D. L. Emery. "Faecal dry matter and nematode infection in parasite-resistant Merino sheep in Australia". Proceedings of the British Society of Animal Science 2009 (aprile 2009): 29. http://dx.doi.org/10.1017/s1752756200028684.
Testo completoAbstract (sommario):
Scouring (diarrhoea) is a major concern for sheep producers as the accumulation of faecal material (dags) around the breech pre-disposes sheep to flystrike. Scouring occurs when the consistency of faeces is fluid with a low percentage of dry matter. In temperate areas such as the southern half of Australia, New Zealand and the United Kingdom, scouring is associated with ingestion of parasitic nematode larvae, mainly Teladorsagia circumcincta and Trichostrongylus colubriformis (Larsen et al., 1994). Breeding sheep to be resistant to these nematodes is a sustainable parasite-control strategy due to reduced reliance on chemical treatment. However, in adult sheep, scouring appears equally prevalent in resistant animals and, in some environments, is even more severe than in susceptible sheep (Karlsson et al., 2004). In this experiment, we investigated how faecal dry matter (FDM) in sheep from a flock bred for resistance to parasitic nematodes changed when challenged with infective larvae. We expected that FDM would be lower in challenged sheep compared to unchallenged controls, and FDM would also be lower in sheep with high dag scores compared to sheep with low dag scores.
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Brown, D. J., e N. M. Fogarty. "Genetic relationships between internal parasite resistance and production traits in Merino sheep". Animal Production Science 57, n. 2 (2017): 209. http://dx.doi.org/10.1071/an15469.
Testo completoAbstract (sommario):
Breeding Merino sheep that are resistant to internal parasites alleviates the high costs associated with treatment of worm infestation and loss of production, as well as mitigating the development of anthelmintic resistance among the major worm species. Faecal worm egg count ((cube root transformation), wec) can be used in sheep as a measure of internal parasite resistance. Accurate estimates of genetic parameters for wec are required for calculation of Australian Sheep Breeding Values and inclusion of worm resistance in sheep breeding programs. This study provides updated estimates of heritability for wec and its genetic correlations with production traits. Data were analysed from a wide range of Australian and New Zealand Merino sheep in the MERINOSELECT database, which included 141 flocks with 801 flock years and up to 217 137 animals with wec recorded in at least one of four ages (W = weaning, P = post weaning, Y = yearling, H = hogget). The heritability estimates ranged from 0.16 ± 0.01 for Ywec to 0.29 ± 0.01 for Wwec, with generally high genetic correlations between the ages. Bivariate analyses estimated genetic correlations between wec at the various ages and growth, carcass quality, reproduction and wool production traits at various ages. These genetic correlations were generally small or close to zero, albeit with some significantly different from zero. The moderate heritability for wec (0.2–0.3) and its high phenotypic variation (coefficient of variation >30%) shows that relatively rapid selection response for worm resistance could be achieved. Inclusion of wec in sheep breeding programs to increase worm resistance would be expected to have little if any impact on other important production traits. These genetic parameters have been incorporated into MERINOSELECT by Sheep Genetics to provide Australian Sheep Breeding Values for wec and appropriate indices for wool and meat production. There is evidence that genotype × environment interactions may be important in some environments by reducing the accuracy of Australian Sheep Breeding Values for wec. Hence it may be prudent for breeders to implement strategies that manage the risk of any impact of genotype × environment on their breeding program.
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Daetwyler, H. D., J. M. Hickey, J. M. Henshall, S. Dominik, B. Gredler, J. H. J. van der Werf e B. J. Hayes. "Accuracy of estimated genomic breeding values for wool and meat traits in a multi-breed sheep population". Animal Production Science 50, n. 12 (2010): 1004. http://dx.doi.org/10.1071/an10096.
Testo completoAbstract (sommario):
Estimated breeding values for the selection of more profitable sheep for the sheep meat and wool industries are currently based on pedigree and phenotypic records. With the advent of a medium-density DNA marker array, which genotypes ~50 000 ovine single nucleotide polymorphisms, a third source of information has become available. The aim of this paper was to determine whether this genomic information can be used to predict estimated breeding values for wool and meat traits. The effects of all single nucleotide polymorphism markers in a multi-breed sheep reference population of 7180 individuals with phenotypic records were estimated to derive prediction equations for genomic estimated breeding values (GEBV) for greasy fleece weight, fibre diameter, staple strength, breech wrinkle score, weight at ultrasound scanning, scanned eye muscle depth and scanned fat depth. Five hundred and forty industry sires with very accurate Australian sheep breeding values were used as a validation population and the accuracies of GEBV were assessed according to correlations between GEBV and Australian sheep breeding values . The accuracies of GEBV ranged from 0.15 to 0.79 for wool traits in Merino sheep and from –0.07 to 0.57 for meat traits in all breeds studied. Merino industry sires tended to have more accurate GEBV than terminal and maternal breeds because the reference population consisted mainly of Merino haplotypes. The lower accuracy for terminal and maternal breeds suggests that the density of genetic markers used was not high enough for accurate across-breed prediction of marker effects. Our results indicate that an increase in the size of the reference population will increase the accuracy of GEBV.
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Mortimer, S. I., K. D. Atkins, S. J. Semple e N. M. Fogarty. "Predicted responses in Merino sheep from selection combining visually assessed and measured traits". Animal Production Science 50, n. 10 (2010): 976. http://dx.doi.org/10.1071/an10085.
Testo completoAbstract (sommario):
Visually assessed traits for wool quality and ease of management are important to Merino sheep breeders and need to be considered in breeding programs. The present study reports on the predicted correlated responses in visual traits from selection using a range of standard MERINOSELECT™ indices available for use in Australian Merino breeding programs. The effect of including a visual trait in the index is also reported. The visual scored traits were classer grade, wool quality (handle, character and colour), conformation (neck and body wrinkle, front and back leg structure) and fleece rot. The indices covered a range of micron premiums of varying emphasis on increasing fleece weight and reducing fibre diameter. The indices were for Merino wool enterprises (Merino 14%, Merino 7% and Merino 3.5%) and Merino dual purpose wool and meat enterprises (Dual Purpose 7% and Dual Purpose 3.5%). The breeding objectives for the indices included fleece weight, fibre diameter, coefficient of variation of fibre diameter, staple strength, bodyweight and reproduction. Selection over 10 years using the standard MERINOSELECT™ indices is predicted to result in a small correlated improvement in the wool quality traits and classer grade, with a slight deterioration in fleece rot score. The improvement in wool handle, character and colour are greater with those indices that have a greater emphasis on reducing fibre diameter than with those increasing fleece weight. Indices with more emphasis on increased fleece weight than on reduced fibre diameter are predicted to result in small increases in neck and body wrinkle scores and a slight deterioration in wool colour. Inclusion of classer grade, handle, character or colour provided slight extra gains in fleece weight for indices that emphasised reduced fibre diameter through increased accuracy of selection.
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Blumer, S. E., G. E. Gardner, M. B. Ferguson e A. N. Thompson. "Environmental and genetic factors influence the liveweight of adult Merino and Border Leicester × Merino ewes across multiple sites and years". Animal Production Science 56, n. 4 (2016): 775. http://dx.doi.org/10.1071/an14419.
Testo completoAbstract (sommario):
Variation in liveweight change in the ewe flock during periods of poor nutrition can affect farm profitability through the effects of liveweight loss on potential stocking rate, management interventions including supplementary feeding, and ewe and lamb survival and productivity. There is variation between individual animals in their ability to manage periods of poor nutrition, but the links between liveweight change and breeding values in the adult ewe flock have not been quantified. We analysed 5216 liveweight profiles for 2772 ewes managed over 3 years at eight sites across Australia, to define the relative effects of environment, reproductive performance and breeding values on liveweight change. The range in liveweight loss varied from 1.3 kg to 21.6 kg, and for liveweight gain from 0.4 kg to 28.1 kg. Site and year had the largest influence on liveweight change, which demonstrates that seasonal conditions and management were the most important factors influencing liveweight change. Liveweight loss was influenced by previous and current reproductive performance but these effects were small in comparison to the effects of site and year. There were mixed associations with sire breeding values for growth, fat and muscle depending on site. An increase in sire breeding values for fat by 1 mm was associated with a reduction in liveweight loss by up to 1.3 kg regardless of ewe breed, and this was more evident at sites where ewes lost a greater proportion of their liveweight. While management had the greatest effect on liveweight change, there appears to be scope to use breeding values to select sheep that will lose less weight during periods of poor nutrition in some environments.
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Swan, Andrew A., Daniel J. Brown e Julius H. J. van der Werf. "Genetic variation within and between subpopulations of the Australian Merino breed". Animal Production Science 56, n. 1 (2016): 87. http://dx.doi.org/10.1071/an14560.
Testo completoAbstract (sommario):
Genetic variation within and between Australian Merino subpopulations was estimated from a large breeding nucleus in which up to 8500 progeny from over 300 sires were recorded at eight sites across Australia. Subpopulations were defined as genetic groups using the Westell–Quaas model in which base animals with unknown pedigree were allocated to groups based on their flock of origin if there were sufficient ‘expressions’ for the flock, or to one of four broad sheep-type groups otherwise (Ultra/Superfine, Fine/Fine-medium, Medium/Strong, or unknown). Linear models including genetic groups and additive genetic breeding values as random effects were used to estimate variance components for 12 traits: yearling greasy and clean fleece weight (ygfw and ycfw), yearling mean and coefficient of variation of fibre diameter (yfd and ydcv), yearling staple length and staple strength (ysl and yss), yearling fibre curvature (ycuv), yearling body wrinkle (ybdwr), post-weaning weight (pwt), muscle (pemd) and fat depth (pfat), and post-weaning worm egg count (pwec). For the majority of traits, the genetic group variance ranged from approximately equal to two times larger than the additive genetic (within group) variance. The exceptions were pfat and ydcv where the genetic group to additive variance ratios were 0.58 and 0.22, respectively, and pwec and yss where there was no variation between genetic groups. Genetic group correlations between traits were generally the same sign as corresponding additive genetic correlations, but were stronger in magnitude (either more positive or more negative). These large differences between genetic groups have long been exploited by Merino ram breeders, to the extent that the animals in the present study represent a significantly admixed population of the founding groups. The relativities observed between genetic group and additive genetic variance components in this study can be used to refine the models used to estimate breeding values for the Australian Merino industry.
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Behrendt, Karl. "Price risk exposure of Australian Merinos – is it in the bloodline?" Animal Production Science 54, n. 9 (2014): 1317. http://dx.doi.org/10.1071/an14305.
Testo completoAbstract (sommario):
Sheep producers and their advisors utilise Australian Merino bloodline trial data to guide future sheep breeding objectives and ram selection. To adequately assess the economic outcomes from different bloodlines in the decision making process, there is a need to consider the impact of wool and sheep meat price risk. Using a steady-state wether flock model that accounts for the lifetime productivity of 268 reported Merino bloodlines and stochastic dependency in weekly wool and sheep meat prices from 28 June 2005 to 10 November 2011, gross incomes per dry sheep equivalent (GI/DSE) were calculated for a weekly time step. The analysis found that across all bloodlines and market price scenarios, GI/DSE ranged between AU$13.92 and AU$67.83, with an overall mean of AU$32.60. The individual means of bloodlines across the time series ranged from AU$37.46 to AU$25.19 GI/DSE. The coefficient of variation, used as the measure of relative risk for each bloodline, ranged from 0.24 to 0.30 with a mean of 0.25. The analysis showed that a bloodlines exposure to price risk has a curvilinear relationship to fibre diameter and fleece weight. The results from a risk-reward point of view indicate that the majority of Australian Merino bloodlines are risk-inefficient. This suggests Australian sheep producers have a significant opportunity to increase net returns and reduce price risk exposure by identifying and switching to more risk-efficient bloodlines.
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Granleese, T., S. A. Clark, A. A. Swan e J. H. J. van der Werf. "Increased genetic gains in multi-trait sheep indices using female reproductive technologies combined with optimal contribution selection and genomic breeding values". Animal Production Science 57, n. 10 (2017): 1984. http://dx.doi.org/10.1071/an15440.
Testo completoAbstract (sommario):
Female reproductive technologies such as multiple ovulation and embryo transfer (MOET) and juvenile in vitro fertilisation and embryo transfer (JIVET) can produce multiple offspring per mating in sheep and cattle. In breeding programs this allows for higher female selection intensity and, in the case of JIVET, a reduction in generation interval, resulting in higher rates of genetic gain. Low selection accuracy of young females entering JIVET has often dissuaded producers from using this technology. However, genomic selection (GS) could increase selection accuracy of candidates at a younger age to help increase rates of genetic gain. This increase might vary for different traits in multiple trait breeding programs depending on genetic parameters and the practicality of recording, particularly for hard to measure traits. This study used both stochastic (animals) and deterministic (GS) simulation to evaluate the effect of reproductive technologies on the genetic gain for various traits in sheep breeding programs, both with and without GS. Optimal contribution selection was used to manage inbreeding and to optimally assign reproductive technologies to individual selection candidates. Two Australian sheep industry indexes were used – a terminal sire index that focussed on growth and carcass traits (the ‘Lamb 2020’ index) and a Merino index that focuses on wool traits, bodyweight, and reproduction (MP+). We observed that breeding programs using artificial insemination or natural mating (AI/N) + MOET, compared with AI/N alone, yielded an extra 39% and 27% genetic gain for terminal and Merino indexes without GS, respectively. However, the addition of JIVET to AI/N + MOET without GS only yielded an extra 1% genetic gain for terminal index and no extra gain in the Merino index. When GS was used in breeding programs, we observed AI/N + MOET + JIVET outperformed AI/N + MOET by 21% and 33% for terminal and Merino indexes, respectively. The implementation of GS increased genetic gain where reproductive technologies were used by 9–34% in Lamb 2020 and 37–98% in MP+. Individual trait response to selection varied in each breeding program. The combination of GS and reproductive technologies allowed for greater genetic gain in both indexes especially for hard to measure traits, but had limited effect on the traits that already had a large amount of early age records.
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Salvatore, L., D. Allen, K. L. Butler, D. Tucman, A. Elkins, D. W. Pethick e F. R. Dunshea. "Factors affecting the concentration of short branched-chain fatty acids in sheep fat". Australian Journal of Experimental Agriculture 47, n. 10 (2007): 1201. http://dx.doi.org/10.1071/ea07037.
Testo completoAbstract (sommario):
The concentration of short branched-chain fatty acids, specifically 4-methyloctanoic acid (MOA) and 4-methylnonanoic acid (MNA), in subcutaneous fat were determined in five genotypes (Poll Dorset × Border Leicester Merino, Poll Dorset × Merino, Poll Dorsetmuscling × Merino, Merino × Merino, Border Leicester × Merino) of Australian sheep. In total, 264 ewes and wethers, either 8 or 22 months of age, were selected for genotype, age and gender. These animals were sired by 16 rams that were selected for growth based on estimated breeding values (EBVs), except for one group (Poll Dorsetmuscling × Merino), which was selected for muscling based on EBVs. There was a strong relationship between the concentration of MOA and MNA at 8 and 22 months of age. There were no differences between lambs sired by Poll Dorset rams selected for muscling or growth. The 8- and 22-month-old Poll Dorset × Merino sheep had higher levels of MOA and MNA compared with the other genotypes (P < 0.001). At 8 months of age, the wethers had higher levels of MOA and MNA (P < 0.001) than the ewes of the same genotype. There was a strong relationship (P < 0.001) between MOA and MNA and the fat and lean percentage for 22-month-old ewes. Effects of sire, dam and slaughter day (at the same slaughter age) on MOA and MNA were also found. The results suggest that there is good feasibility for selection against animals at risk of possessing higher levels of short branched-chain fatty acids.
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Fogarty, N. M., E. Safari, P. J. Taylor e W. Murray. "Genetic parameters for meat quality and carcass traits and their correlation with wool traits in Australian Merino sheep". Australian Journal of Agricultural Research 54, n. 7 (2003): 715. http://dx.doi.org/10.1071/ar03047.
Testo completoAbstract (sommario):
Estimates of genetic parameters for carcass traits in Merino sheep are presented, including muscle pH and colour, which are indicators of meat quality. The inclusion of these in the parameter set for genetic evaluation will provide the basis for more accurate estimated breeding values and the design of better breeding programs for improving meat traits in straightbred Merino sheep and crossbred lamb production. Data from 1045, nineteen-month-old Merino rams, the progeny of 125 sires from 3 strains that are representative of the industry, were used. Heritability and genetic correlations were estimated by fitting an animal model using a REML procedure in univariate and multivariate analyses. The traits included fasted pre-slaughter liveweight; dressing %; carcass tissue depth at the GR site (FATGR); fat depth at the C site (FATC); eye muscle depth (EMD), width (EMW), and area (EMA); ultimate pH and colour (L*, a*, b*) of the eye muscle. Multivariate analyses were used to estimate genetic correlations among meat traits and between wool traits (clean wool weight and mean fibre diameter) and selected carcass and meat traits. Estimates of heritability were: liveweight 0.51 (±0.10), dressing % 0.39 (±0.10), FATGR 0.33 (±0.09), FATC 0.20 (±0.08), EMD 0.27 (±0.08), EMW 0.15 (±0.07), EMA 0.23 (±0.08), muscle pH 0.27 (±0.09), and 0.14 (±0.07), 0.02 (±0.06), and 0.04 (±0.06) for the meat colour measurements L*, a*, and b* respectively. There was a favourable genetic correlation between muscle pH and colour L* of –0.56 (±0.23). There were also significant genetic correlations between wool weight and FATGR (–0.34 ± 0.16) and between mean fibre diameter and muscle colour L* (–0.66 ± 0.27). The study indicates that there is genetic variation for carcass traits, including indicators of meat quality, with scope for selection to improve meat production and quality in Merino sheep.
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Mortimer, S. I., J. H. J. van der Werf, R. H. Jacob, D. W. Pethick, K. L. Pearce, R. D. Warner, G. H. Geesink et al. "Preliminary estimates of genetic parameters for carcass and meat quality traits in Australian sheep". Animal Production Science 50, n. 12 (2010): 1135. http://dx.doi.org/10.1071/an10126.
Testo completoAbstract (sommario):
Using performance from progeny born in 2007 and 2008 generated by the Information Nucleus program of the Cooperative Research Centre for Sheep Industry Innovation, preliminary estimates of heritability were obtained for a range of novel carcass and meat attributes of lamb relevant to consumers, including carcass characteristics, meat quality and nutritional value of lamb. Phenotypic and genetic correlations of live animal traits with carcass composition and meat quality traits were also estimated. The data were from progeny located at eight sites, sired by 183 rams from Merino, maternal and terminal meat breeds and were representative of the Merino, Border Leicester × Merino, Terminal × Merino and Terminal × Border Leicester-Merino production types of the Australian sheep industry. Data were available from 7176 lambs for weaning weight, 6771 lambs for ultrasound scanning and 4110 lambs for slaughter traits. For the novel meat quality traits, generally moderate to high heritability estimates were obtained for meat quality measures of shear force (0.27 aged 1 day, 0.38 aged 5 days), intramuscular fat (0.39), retail meat colour (range of 0.09 to 0.44) and myoglobin content (0.22). The nutritional value traits of omega-3 fatty acids and iron and zinc contents tended to have low to moderate heritabilities (0.11–0.37), although these were based on fewer records. Fresh meat colour traits were of low to moderate heritability (0.06–0.21) whereas measures of meat pH were of low heritability (~0.10). For the carcass traits, estimates of heritability were moderate to high for the various measures of carcass fat (0.18–0.50), muscle weight (0.22–0.35), meat yield (0.24–0.35), carcass muscle dimensions (0.25–0.34) and bone weight (0.27). Results indicate that for most lamb carcass and meat quality traits there is sufficient genetic variation for selection to alter successfully these characteristics. Additionally, most genetic correlations of live animal assessments of bodyweight, muscle and subcutaneous fat with the carcass and meat quality traits were favourable. Appropriate definition of breeding objectives and design of selection indexes should be able to account for the small unfavourable relationships that exist and achieve the desired outcomes from breeding programs.
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Qiu, Xiaoyan, Xiong Xiao, Nan Li, Wenhui Ling, Mingyu Wang e Yuemin Li. "Association of steroid 17-alpha-hydroxylase/17,20 lyase (CYP17) single nucleotide polymorphism (SNP) 628 and dopamine receptor D2 (DRD2) SNP939 genotypes with sheep reproductive performance". Reproduction, Fertility and Development 31, n. 4 (2019): 743. http://dx.doi.org/10.1071/rd18069.
Testo completoAbstract (sommario):
In a previous study we investigated the association between two single nucleotide polymorphism (SNP) genotypes, namely steroid 17-alpha-hydroxylase/17,20 lyase (CYP17) SNP628 and dopamine receptor D2 (DRD2) SNP939, with two temperaments (calm and nervous) in Australian Merino sheep and concluded that the DRD2 SNP939 T/T genotype combined with the CYP17 SNP628 G/G genotype is associated with a calm temperament and could be used as a potential marker for calm sheep, whereas the DRD2 SNP939C allele combined with the CYP17 SNP628 A/A genotype is associated with a nervous temperament and could be used as a potential marker for nervous sheep. In sheep, the association between temperament and reproductive performance has been determined, but the association of these two SNP genotypes with sheep reproduction has not been investigated. Therefore, using Chinese Sinkiang Merino sheep, the present study investigated the association of the two CYP17 SNP628 and DRD2 SNP939 genotypes with sheep reproductive performance. Sheep with the DRD2 SNP939 T/T genotype combined with the CYP17 SNP628 G/G genotype had a higher ovulation rate, multiple gestation rate, better maternal behaviour and lower lamb mortality. Thus, the results of this study contribute to our knowledge of the association between genotypes and reproduction in sheep, which is beneficial for sheep genetics and breeding.
17
Aboneev, Vasily, Dmitry Aboneev, Ekaterina Aboneeva, Safarbi Kazanchev e Dastanbek Baimukanov. "Results of using different breed studs in commercial fine wool sheep breeding". E3S Web of Conferences 262 (2021): 02016. http://dx.doi.org/10.1051/e3sconf/202126202016.
Testo completoAbstract (sommario):
This work presents the material of research and production experiments on the crossing of stud rams of the North Caucasian meat and wool breed and Australian meat merino with fine wool ewes of a commercial herd. It is identified that the use of North Caucasian rams on fine wool ewes serves to increase the fertilizing ability and milk production of the breeding stock, to increase viability and resistance of young animals, as confirmed by the best morphometrical differences of crossbred offspring placentas. Crossbred offspring from semi-fine wool rams had a large live weight at birth at 21 days and at 4 months of age. The use of Australian producers did not have a significant effect on the above indicators of economically useful traits in comparison with purebred breeding.
18
Sahana, G., S. C. Gupta e A. E. Nivsarkar. "Garole: The prolific sheep of India". Animal Genetic Resources Information 31 (aprile 2001): 55–63. http://dx.doi.org/10.1017/s1014233900001486.
Testo completoAbstract (sommario):
SummaryA survey on Garole sheep was carried out in the breeding tract for breed characterization. Garole sheep are distributed in the Sundarban region of West Bengal in India. It is a small-sized breed known for its prolificacy and adaptation to the saline marshy land of the Sundarban region. It is believed that these sheep contributed to the prolificacy gene in Booroola Merino sheep of Australia. The breeding tract of Garole sheep falls under the Coastal Saline Zone of West Bengal and the climate of this region is hot and humid. The population of Garole sheep was 206 720 in 1994–1995. This breed is maintained by marginal farmers and landless labourers. Flocks are stationary and average flock size ranges from three to five. They graze on rice fallow land and natural grass cover on the roadsides and water channels. Garole sheep have the ability to graze in knee deep conditions in marshy land. Their colour is generally white. Some animals of black or brown colour are also seen. The male is generally horned and females are polled. They have three distinct types of ears; small, medium and long. Average adult weights in male and females are 15 and 12 kg, respectively. Twin and triplet births are common. The Garole sheep are reared for mutton production. Farmers generally do not shear wool. Fleece is of a coarse quality and is used as bedding material.
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Walkom, S. F., F. D. Brien, M. L. Hebart, S. I. Mortimer e W. S. Pitchford. "Season and reproductive status rather than genetics factors influence change in ewe weight and fat over time. 3. Analysis of Merino ewes". Animal Production Science 54, n. 6 (2014): 821. http://dx.doi.org/10.1071/an13249.
Testo completoAbstract (sommario):
The profitability of southern Australian sheep production systems depends on the optimisation of stocking rates by meeting the nutritional demands of the breeding ewe while effectively utilising grown pasture. The aim of the study was to evaluate the genetic variation in liveweight and body condition of Merino ewes across their breeding life within a wool-based enterprise. The results were consistent with findings in crossbred ewes and showed that the genetic component of weight and body condition remained constant across the production cycle and age. The overall additive genetic effect accounted for 92% of the genetic variation in weight of Merino ewes bred across five production cycles. A genetic correlation of 0.85 suggested that ewes that were superior at maintaining their condition when rearing a single lamb would maintain this superiority when rearing multiple lambs. To improve weight and condition of Merino ewes during the ‘tough’ times, when nutrient requirements are not met by the pasture, selection can be made at any time and this will result in increased genetic condition at all times.
20
Walkom, S. F., A. N. Thompson, E. Bowen e D. J. Brown. "Weaner survival is heritable in Australian Merinos and current breeding objectives are potentially leading to a decline in survival". Animal Production Science 59, n. 1 (2019): 35. http://dx.doi.org/10.1071/an17151.
Testo completoAbstract (sommario):
There is little evidence to show that mortality rates during the period after weaning are improving over time in Australian sheep. The average mortality rate of Merino lambs during the post-weaning period has been estimated to be 5.2%. The present study explored the potential for producers to breed for improved survival rates during the post-weaning period and the potential impact this would have on key production traits. A total of 122526 weaner survival (mortality) records were obtained from 18 Merino flocks, between 1989 and 2014, encompassing a wide variety of Australian Merino sheep types and production systems. The heritability of weaner survival from a sire model was estimated to be 0.07 ± 0.01 and was significantly greater than zero. The survival of lambs post-weaning was significantly influenced by weaning weight, with higher survival rates observed in the heavier lambs. The phenotypic relationship with weight indicates that selection for heavier weaning and post-weaning weights, and in turn larger growth rates, will improve survival rates. There is genetic variation in weaner survival not explained by the relationship with weaning weight. Weight-corrected weaner survival was antagonistically genetically correlated with fleece weight. Due to these antagonistic genetic relationships selection based on popular MERINOSELECT indexes is leading to a very small reduction in the survival rate of lambs after weaning through to the post-weaning stage. To prevent a decline in weaner survival, producers are advised to record weaner survival and include it in their breeding objective.
21
Ponnampalam, E. N., D. L. Hopkins, K. L. Butler, F. R. Dunshea e R. D. Warner. "Genotype and age effects on sheep meat production. 2. Carcass quality traits". Australian Journal of Experimental Agriculture 47, n. 10 (2007): 1147. http://dx.doi.org/10.1071/ea07001.
Testo completoAbstract (sommario):
The present study examines carcass quality traits in different genotypes of Australian sheep slaughtered at 4, 8, 14 and 22 months of age. Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Merino × Merino (M × M) and Border Leicester × Merino (BL × M) genotypes were compared. Sires were selected on the basis of growth (PDg, M and BL) and muscle (PDm) using estimated breeding values (EBVs). Approximately 150 mixed sex animals were slaughtered at each age (595 in total for the four slaughters) and carcass quality traits, including hot carcass weight, loin and semitendinosus (ST) muscle weights, GR fat, fat C, rump fat depth and eye muscle area (EMA), were determined at 45 min to 3 days postslaughter. With age, all carcass quality traits increased in magnitude. Merinos produced the lightest and leanest carcasses (P < 0.01) with lowest values in nearly all the carcass quality traits. At 4 and 8 months of age carcass and loin weights, EMA and GR fat measures were greater (P < 0.01) in second-cross PDg × BLM sheep than all other genotypes. However, traits related to muscle content were similar between first- and second-cross Poll Dorset genotypes at 14 and 22 months of age. The BL × M genotype had lower values than the PD × M genotypes for these traits, at all ages. Traits related to carcass fatness showed that sheep with Border Leicester genetics tend to deposit more fat (P < 0.001) in the carcass than those with Merino or Poll Dorset genetics from 14 months of age onwards. Most carcass quality traits did not differ (P > 0.05) between first-cross Poll Dorset genotypes selected for growth or muscling (PDg × M v. PDm × M). Sires with high muscling EBVs are associated more with shorter carcass length than low muscling EBVs. From ~8 months of age, wethers had greater values (P < 0.05) than ewes of the same age for most carcass quality traits related to size and muscle development, but no effect was present for carcass quality traits that were related to fat deposition. It was clear that the carcass weight of M × M at 8 and 14 months were similar to that observed in PDg × BLM at 4 and 8 months, respectively. Loin weights of M × M and BL × M at 13 and 8 months were similar to that weights observed in PDg × BLM at 8 and 4 months of age, respectively. Animals slaughtered to a muscle weight specification will reach the target at a younger age when they have more Poll Dorset than Border Leicester background genetics. Alternatively animals slaughtered at a specified fat score (using fat C or rump fat depth) will reach the specification at a younger age when they have more Border Leicester than Poll Dorset genetics.
22
Moghaddar, N., A. A. Swan e J. H. J. van der Werf. "Genomic prediction of weight and wool traits in a multi-breed sheep population". Animal Production Science 54, n. 5 (2014): 544. http://dx.doi.org/10.1071/an13129.
Testo completoAbstract (sommario):
The objective of this study was to predict the accuracy of genomic prediction for 26 traits, including weight, muscle, fat, and wool quantity and quality traits, in Australian sheep based on a large, multi-breed reference population. The reference population consisted of two research flocks, with the main breeds being Merino, Border Leicester (BL), Poll Dorset (PD), and White Suffolk (WS). The genomic estimated breeding value (GEBV) was based on GBLUP (genomic best linear unbiased prediction), applying a genomic relationship matrix calculated from the 50K Ovine SNP chip marker genotypes. The accuracy of GEBV was evaluated as the Pearson correlation coefficient between GEBV and accurate estimated breeding value based on progeny records in a set of genotyped industry animals. The accuracies of weight traits were relatively low to moderate in PD and WS breeds (0.11–0.27) and moderate to relatively high in BL and Merino (0.25–0.63). The accuracy of muscle and fat traits was moderate to relatively high across all breeds (between 0.21 and 0.55). The accuracy of GEBV of yearling and adult wool traits in Merino was, on average, high (0.33–0.75). The results showed the accuracy of genomic prediction depends on trait heritability and the effective size of the reference population, whereas the observed GEBV accuracies were more related to the breed proportions in the multi-breed reference population. No extra gain in within-breed GEBV accuracy was observed based on across breed information. More investigations are required to determine the precise effect of across-breed information on within-breed genomic prediction.
23
Butler, LG, SR Corkrey, IJ Knox, G. Hannan e RP Thomson. "Perceptions and knowledge of measurement in selection programs: a survey of stud Merino breeders in Australia". Australian Journal of Experimental Agriculture 35, n. 6 (1995): 681. http://dx.doi.org/10.1071/ea9950681.
Testo completoAbstract (sommario):
A total of 329 (25%) stud Merino breeders returned a survey designed to evaluate their knowledge of, and attitudes to, objective measurement in sheep breeding and performance recording. The data were analysed by log-linear regression techniques. There was overwhelming agreement that performance records were not as valid as traditional methods, but there was general agreement that measurement improves accuracy of selection, increases genetic gain, assists ram buyers and breeders, and increases flock earnings. There is a significant concern regarding the accuracy of fleece tests. Most respondents (60%) intend to increase their use of measurement, although the common attitude was that measurement only gives back-up to visual assessment. Some answers demonstrated a lack of understanding of the principles of applying measurement. There appears to be a difference between breeders and those more closely involved with technical genetics in interpretation of the term 'breeding objective'. Department of Agriculture Officers and Stock Agents rated poorly as sources of information. Rural newspapers and magazines are confirmed as useful media for awareness. It was concluded that a number of barriers to adoption of objective measurement and performance recording need to be overcome, including suspicion about the accuracy of the fleece tests, and the ram age at which testing can be conducted with confidence.
24
Ponzoni, R. W. "A profit equation for the definition of the breeding objective of Australian merino sheep". Journal of Animal Breeding and Genetics 103, n. 1-5 (12 gennaio 1986): 342–57. http://dx.doi.org/10.1111/j.1439-0388.1986.tb00096.x.
Testo completo
25
Sawyer, Gregory, Danielle Webster e Edward Narayan. "Measuring wool cortisol and progesterone levels in breeding maiden Australian merino sheep (Ovis aries)". PLOS ONE 14, n. 4 (8 aprile 2019): e0214734. http://dx.doi.org/10.1371/journal.pone.0214734.
Testo completo
26
Eady, S. J., R. R. Woolaston, R. W. Ponzoni, R. P. Lewer, H. W. Raadsma e A. A. Swan. "Resistance to nematode parasites in Merino sheep: correlation with production traits". Australian Journal of Agricultural Research 49, n. 8 (1998): 1201. http://dx.doi.org/10.1071/a98069.
Testo completoAbstract (sommario):
Merino sheep representing a range of bloodlines in resource flocks located across Australia were tested for resistance to gastro-intestinal nematodes. These flocks included the JB Pye Flock (Camden, NSW), Katanning Base Flock (Katanning, WA), Turretfield Merino Resource Flock (Rosedale, SA), and the CSIRO Finewool Flock (Armidale, NSW) and included a total of 328 sire groups. Resistance to nematodes was measured by faecal egg count (FEC). Data were also available for greasy and clean fleece weight (GFW and CFW, respectively), fibre diameter (FD), and body weight (BW) at a range of ages from weaning to 21 months. Variance components were estimated by restricted maximum likelihood, fitting an animal model and estimating covariances in a series of bivariate analyses. Phenotypic correlations between FEC0·33 and production traits were all close to zero ( –0·09–0·02). Genetic correlations between FEC0·33 and production traits were –0·20, –0·18, and –0·26 for weaning weight, 10-month BW, and 16-month BW, respectively; 0·21, –0·06, and 0·21 for 10-month GFW, 16-month GFW, and 21-month GFW; 0·21, –0·05, and 0·07 for 10-month CFW, 16-month CFW, and 21-month CFW; and –0·09, –0·12, and 0·04 for 10-month FD, 16-month FD, and 21-month FD. When estimates were pooled for all fleece traits and all BW traits, the genetic correlations between FEC0·33 and GFW, CFW, FD, and BW were 0·15, 0·10, –0·06, and –0·21, respectively. Using pooled estimates for CFW, FD, and BW, selection for a breeding objective based on production traits alone would lead to an unfavourable correlated response in FEC0·33 of approximately 1% per year.
27
Benavides, M. V., S. Damak e A. P. Maher. "A putative resistant DNA marker for wool yellowing susceptibility in sheep". Genetics and Molecular Biology 23, n. 2 (giugno 2000): 341–46. http://dx.doi.org/10.1590/s1415-47572000000200017.
Testo completoAbstract (sommario):
An Australian Merino flock was screened for low (resistant) and high (susceptible) yellow predictive colour (YPC) breeding values in order to compare extreme individuals using the differential display of mRNA technique. One differentially expressed cDNA band was visualised only in the resistant group. This band showed no identity with the DNA sequences of public databases; however, they showed short homologies with three database sequences related to transmembrane signalling functions. The use of these candidate genes as DNA markers needs to be confirmed against sheep with a wide range of susceptibility to wool yellowing to verify the results.
28
Huisman, A. E., D. J. Brown, A. J. Ball e H. U. Graser. "Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 1. Description of traits, model comparison, variance components and their ratios". Australian Journal of Experimental Agriculture 48, n. 9 (2008): 1177. http://dx.doi.org/10.1071/ea08119.
Testo completoAbstract (sommario):
Both wool and sheep meat industries are interested in sheep that have a high reproduction performance and are resistant to internal parasites, in addition to the traditional traits. There is considerable interest in breeding sheep for wool, carcass, reproductive and internal parasite resistance traits simultaneously. The objective of this study was to estimate single trait genetic parameters for 40 traits recorded in Merino sheep, covering bodyweight, carcass, wool, reproduction and internal parasite resistance traits. This also involved determining the appropriate models. The results from this study will be used to review the genetic parameters used in the routine genetic evaluations conducted by Sheep Genetics. The most appropriate models included a maternal genetic effect and covariance between direct and maternal genetic effects for most of the bodyweight traits, greasy and clean fleece weight, fibre diameter and coefficient of variation of fibre diameter. The permanent environment due to the dam was not included for any trait. There was considerable genetic variation in most traits analysed; lowest heritabilities (0.09–0.10) were found for number of lambs born and weaned per lambing opportunity, and highest heritabilities (0.62–0.77) for fibre diameter. The estimated heritabilities and genetic variances, in combination with the estimated correlations, indicate that there is potential to make genetic improvement in most traits currently recorded in Australian Merino sheep.
29
Newton, J. E., D. J. Brown, S. Dominik e J. H. J. van der Werf. "Impact of young ewe fertility rate on risk and genetic gain in sheep-breeding programs using genomic selection". Animal Production Science 57, n. 8 (2017): 1653. http://dx.doi.org/10.1071/an15321.
Testo completoAbstract (sommario):
Genomic selection could be useful in sheep-breeding programs, especially if rams and ewes are first mated at an earlier age than is the current industry practice. However, young-ewe (1 year old) fertility rates are known to be lower and more variable than those of mature ewes. The aim of the present study was to evaluate how young-ewe fertility rate affects risk and expected genetic gain in Australian sheep-breeding programs that use genomic information and select ewes and rams at different ages. The study used stochastic simulation to model different flock age structures and young-ewe fertility levels with and without genomic information for Merino and maternal sheep-breeding programs. The results from 10 years of selection were used to compare breeding programs on the basis of the mean and variation in genetic gain. Ram and ewe age, availability of genomic information on males and young-ewe fertility level all significantly (P < 0.05) affected expected genetic gain. Higher young-ewe fertility rates significantly increased expected genetic gain. Low fertility rate of young ewes (10%) resulted in net genetic gain similar to not selecting ewes until they were 19 months old and did not increase breeding-program risk, as the likelihood of genetic gain being lower than the range of possible solutions from a breeding program with late selection of both sexes was zero. Genomic information was of significantly (P < 0.05) more value for 1-year-old rams than for 2-year-old rams. Unless genomic information was available, early mating of rams offered no greater gain in Merino breeding programs and increased breeding-program risk. It is concluded that genomic information decreases the risk associated with selecting replacements at 7 months of age. Genetic progress is unlikely to be adversely affected if fertility levels above 10% can be achieved. Whether the joining of young ewes is a viable management decision for a breeder will depend on the fertility level that can be achieved in their young ewes and on other costs associated with the early mating of ewes.
30
Safari, E., N. M. Fogarty, A. R. Gilmour, K. D. Atkins, S. I. Mortimer, A. A. Swan, F. D. Brien, J. C. Greeff e J. H. J. van der Werf. "Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects". Australian Journal of Agricultural Research 58, n. 2 (2007): 169. http://dx.doi.org/10.1071/ar06161.
Testo completoAbstract (sommario):
Accurate estimates of adjustment factors for systematic environmental effects are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate genetic parameters and investigate the significance of various environmental factors for production traits in Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, with over 2700 sires and 25 000 dams. Univariate linear mixed animal models were used to analyse 6 wool, 4 growth, and 4 reproduction traits. This first paper outlines the data structure and the non-genetic effects of age of the animal, age of dam, birth-rearing type, sex, flock, bloodline, and year, which were significant with few exceptions for all production traits. Age of dam was not significant for reproduction traits and fleece yield. Generally, wool, growth, and reproduction traits need to be adjusted for age, birth-rearing type, and age of dam before the estimation of breeding values for pragmatic and operational reasons. Adjustment for animal age in wool traits needs to be applied for clean fleece weight (CFW), greasy fleece weight (GFW), and fibre diameter (FD) with inclusion of 2 age groups (2 years old and >2 years old), but for reproduction traits, inclusion of all age groups is more appropriate. For GFW, CFW, and hogget weight (HWT), adjustment for only 2 dam age groups of maiden and mature ewes seems sufficient, whereas for birth (BWT), weaning (WWT), and yearling (YWT) weights, adjustments need to be applied for all dam age groups. Adjustment for birth-rearing type (single-single, multiple-single, multiple-multiple) is appropriate for wool, growth, and reproduction traits. The implications of adjustment for non-genetic effects are discussed.
31
Bray, M., D. K. Revell, C. S. Bawden e P. I. Hynd. "Keratin gene expression in Merino sheep with divergent wool growth". Australian Journal of Agricultural Research 56, n. 3 (2005): 203. http://dx.doi.org/10.1071/ar03253.
Testo completoAbstract (sommario):
South Australian Merino sheep were selected on the basis of high or low estimated breeding values (EBV) for wool growth rate (W), but with similar bodyweight, follicle density, and mean fibre diameter. Differences in the level of expression of keratin genes were examined in the skin of these sheep to test the hypothesis that divergence in EBV for wool growth is related to the production of wool proteins differing in sulfur (S) content. Further, it was proposed that this differential gene expression would be most pronounced when the supply of S amino acids to the animal was increased. Sheep selected for high EBV (+W) produced more wool per day than low EBV sheep (–W) (on average 32.5 v. 17.7 g/day clean wool, respectively; P < 0.05) but the S content of the wool did not differ between selection groups (2.77% v. 2.87% S, respectively; P = 0.2). Expression of keratin genes including keratin-associated protein KAP 2 (a high S gene), KAP 4 (an ultra-high S gene), KAP 6 (a high glycine/tyrosine gene), and the intermediate filament gene K 2.10, did not differ significantly between +W and –W groups. KAP 2 and K 2.10 each accounted for approximately 5% of the variation in wool growth rate (WGR) but expression of none of the genes examined was significantly related to the S content of the fibre produced. This suggests that differential keratin gene expression was not the source of genetic divergence in WGR. Instead the latter likely reflects a combination of differential cellular rate and growth processes (e.g. rate of bulb cell production, hypertrophy of cortical cells), differences in the relative production of inner root sheath and fibre from the follicle bulb cell population, or differential nutrient uptake into the follicle.
32
Ferguson, M. B., J. M. Young, G. A. Kearney, G. E. Gardner, I. R. D. Robertson e A. N. Thompson. "The value of genetic fatness in Merino ewes differs with production system and environment". Animal Production Science 50, n. 12 (2010): 1011. http://dx.doi.org/10.1071/an10130.
Testo completoAbstract (sommario):
Selection against fatness in the Australian sheep industry has been a priority, but defining the true value of fat requires an understanding of the effects it has on both the value of lamb carcasses and on sheep productivity. A Merino flock with 10 years of reproduction data was used to analyse the correlation between breeding values for fatness at yearling age (YFAT) and the number of lambs born per ewe mated (NLB). In 2 production years, NLB was related (P < 0.01) to YFAT resulting in an extra 14 or 24.5 lambs born per 100 ewes mated per mm of YFAT. Based on these relationships, bio-economic modelling was used to assess the whole-farm value of YFAT for different sheep production systems and for years representing a low, medium and high response of NLB to YFAT. The changes in whole-farm profitability for a 1-mm increase in YFAT varied from $1000 (2%) for a wool enterprise with a low response up to $44 000 (25%) for a lamb enterprise with a high response. Appropriate carcass value discounts for higher YFAT were investigated but were not evident because of the small change in GR fat depth associated with the range of YFAT investigated. In most years there is no impact of YFAT on NLB and therefore profitability, yet in years where Merino ewes with higher YFAT produce higher NLB, ewes with an extra 1 mm of YFAT will be up to 25% more profitable. Therefore, care is required in determining the appropriate selection pressure to be placed on YFAT in Merino selection.
33
Fozi, M. Asadi, J. H. J. Van der Werf e A. A. Swan. "The importance of accounting for maternal genetic effects in Australian fine-wool Merino breeding". Australian Journal of Agricultural Research 56, n. 8 (2005): 789. http://dx.doi.org/10.1071/ar05006.
Testo completoAbstract (sommario):
(Co) variances for greasy fleece weight (GFW), clean fleece weight (CFW), mean fibre diameter (MFD), staple strength (SS), coefficient of variation of fibre diameter (CVFD), birthweight (BW), weaning weight (WW), and yearling weight (YW) were estimated for 5108 Australian Merino sheep from the CSIRO Fine Wool Project, born between 1990 and 1994. Covariances between these traits and number of lambs weaned per ewe joined (NLW) were also estimated. Significant maternal genetic effects were found for GFW, CFW, BW, WW, and YW. Estimates of heritability were biased upwardly when maternal effects were ignored. The maternal heritability estimates for GFW, CFW, BW, WW, and YW were 0.17, 0.15, 0.38, 0.28, and 0.13, respectively. Maternal effects were not important for MFD, CVFD, SS, and NLW. Direct-maternal genetic correlations within each fleece weight and bodyweight trait were estimated to be moderately negative (–0.26 to –0.48). The effect of ignoring maternal genetic effect was explored using selection index theory. Accounting for the maternal effects in both the selection criteria and breeding objective increased the overall response by 14.3%, 4.8%, 2.6%, 1.4%, and 0.0% in 3, 6, 12, 20 and 30% micron premium scenarios, respectively, compared with when the maternal effects were only included in breeding objective. Complete ignorance of the maternal effects led to overestimation in overall response of 2.8–35.7% for different micron premium scenarios in contrast to when the maternal effects were ignored in the selection index weight, but were included in the breeding objective. The results indicate that the maternal genetic effects of fleece weight and bodyweight should be considered in Merino breeding programs.
34
Wray, N. R., e M. E. Goddard. "MOET breeding schemes for wool sheep 2. Selection for adult fleece traits". Animal Science 59, n. 1 (agosto 1994): 87–98. http://dx.doi.org/10.1017/s0003356100007534.
Testo completoAbstract (sommario):
AbstractBenefits of collection of annual versus a single fleece record are investigated for breeding programmes of Australian Merino sheep. Breeding scheme alternatives are based on natural mating (N) or multiple ovulation and embryo transfer (MOET). The breeding objective is assumed to be an adult fleece trait which is expressed annually from a minimum of age 2 years, with a unity genetic correlation between annual records. Initial selection of parents can occur prior to the availability of their adult records, based on records collected at 6,12 or 18 months which have a maximum genetic correlation of 0·8 with the adult trait. Monte Carlo simulation is used to compare breeding programme alternatives, which allows overlapping generations and selection across age groups. MOET schemes select parents of minimum age 19 months in adult (A) schemes, 7 months in juvenile (J) schemes or 13 months when there are two breeding seasons per year. Natural mating results in an average of 1·09 lambs per ewe mated, whilst embryo transfer success rates follow realistic distributions (only 70% of donors giving live lambs) with an average of 3·45 lambs per donor flushed. Estimated breeding values, on which selection is based, are calculated by multiple trait selection index of an individual's own records or by multivariate best linear unbiased prediction (BLUP). In J schemes 7-month-old lambs may be selected on the basis of a pedigree index if no individual record has been collected at 6 months of age. Breeding scheme alternatives are compared on the basis of genetic response, rate of inbreeding and economic ‘income’ which is calculated as genetic response reduced for inbreeding depression, cumulated and discounted over a medium time horizon (14 years). The quantitative benefits of the collection of annual records are dependent on the choice of genetic and phenotypic parameters between traits, but these were chosen from the literature to be representative of annual fleece weight records in Merino sheep. Genetic response to selection and ‘income’ associated with the adult trait is increased by at least 15% in N, A and J schemes compared with when only a single record is collected at 18 months. The advantage of MOET over N schemes and the optimum number of sires to use is unchanged, but the average age of sires is increased. Both annual rate of inbreeding and average age of dams are unchanged. In N schemes, 80% of the benefits of collecting annual records on both sexes can be achieved by collecting records on males alone, whilst in MOET schemes measurement of dams contributes up to 50% of the benefit of the measurement of both sexes. Since MOET schemes have fewer dams to be recorded, the cost-effectiveness of collecting records on females is much higher than in natural mating schemes. Breeding programmes operating two mating seasons each year are found to be a viable alternative to J schemes: although genetic response is less, rate of inbreeding is also less, so that ‘income’ response is approximately equal.
35
Morton, K. M., S. L. Catt, F. K. Hollinshead, W. M. C. Maxwell e G. Evans. "280LAMBS BORN AFTER IN VITRO EMBRYO PRODUCTION FROM PREPUBERTAL LAMB OOCYTES AND FROZEN-THAWED UNSORTED AND SEX-SORTED SPERMATOZOA". Reproduction, Fertility and Development 16, n. 2 (2004): 260. http://dx.doi.org/10.1071/rdv16n1ab280.
Testo completoAbstract (sommario):
Developments in sperm sexing technology have resulted in the birth of a number of offspring after IVF of oocytes from adult animals (Johnson LA, 2000 An. Reprod. Sci. 60–61, 93–107). The aim of this study was to combine sperm sexing technology with juvenile breeding. Merino lambs, 2–3 weeks (n=43) were hormone stimulated (Morton KM et al., 2003 Proc. Soc. Reprod. Fert., P18), and COCs were matured in TCM-199 (Sigma) with 10μgmL−1 p-FSH (Folltropin-V; Bioniche Animal Health Australasia), 10μgmL−1 pLH (Bioniche), and 20% sheep serum (v/v) in a humidified 6% CO2, 5% O2, 89% N2 atmosphere for 22h. Semen collected from Merino rams was diluted and frozen as pellets (Unsorted), or stained with H33342, separated into X and Y sperm using a SX MoFlo (Cytomation Inc., Fort Collins, CO, USA), and frozen as pellets (Sorted). Sperm were prepared for IVF by swim-up under 0.5mL of SOF with 2% sheep serum (v/v; SOF+) for 45min (Unsorted), or diluted in 0.5mL of Sydney IVF Sperm Buffer (Cook IVF, Brisbane, Australia) and centrifuged at 650g for 3min (Sorted). After IVM, oocytes were transferred to SOF+, and cultured with 0.5×106mL−1 (Unsorted) or 1.0×106mL−1 (Sorted) motile sperm for 18h. Presumptive zygotes were transferred to Sydney IVF cleavage and blastocyst medium (Cook IVF) for 3 and 5 days, respectively. Oocyte maturation and fertilization were assessed by orcein staining 18h post-insemination (hpi). Two Day-7 blastocysts were transferred to each recipient ewe (n=9; 3 per group) and pregnancies diagnosed by ultrasound on Day 57 of gestation. Data were analyzed by chi-square test. Oocyte maturation was 83.9% (73/87), and monospermic fertilization did not differ for Unsorted (22/32; 68.7%), X- (6/14; 42.8%), and Y-sperm groups (15/27; 55.6%). Polyspermic fertilization was 9.4% (3/32) and 7.4% (2/27) for the Unsorted and Y groups. Cleavage was reduced with X- and Y-sperm compared with Unsorted, but blastocyst formation (from cleaved oocytes) did not differ (Table 1). There were three (100%), zero (0%), and one (33.3%) pregnancies from Unsorted, X- and Y-embryos, respectively, all of which survived to birth, demonstrating that juvenile breeding can be successfully combined with sperm sexing. Table 1 Cleavage and blastocyst formation after IVF with Unsorted, X- or Y-sperm. Values in parenthesis are percentages
36
Brown, D. J., N. M. Fogarty, C. L. Iker, D. M. Ferguson, D. Blache e G. M. Gaunt. "Genetic evaluation of maternal behaviour and temperament in Australian sheep". Animal Production Science 56, n. 4 (2016): 767. http://dx.doi.org/10.1071/an14945.
Testo completoAbstract (sommario):
The temperament of ewes and maternal behaviour at lambing has been implicated as contributing factors to lamb survival. Some 14 054 records of maternal behaviour score (MBS, 1 = good, 5 = poor) were collected at lamb tagging from 32 breeds of sheep over several years in a variety of environments. Records for two objectively scored temperament traits, flight time from a weighing crate (FT) and agitation score in an isolation box test (IBT) were available on 19 151 and 17 159 animals, respectively. These data were pooled from three sources, which included research and commercial ram breeding flocks. The combined data were also split into three subsets based on breed groups (Merino, Maternal and Terminal) for analyses. Records of weights and number of lambs weaned (NLW), as well as pedigree information was available from the national genetic evaluation database. The heritability estimates from the combined analyses were 0.20 ± 0.02 for MBS, 0.18 ± 0.02 for FT and 0.26 ± 0.02 for IBT, with a repeatability of 0.24 ± 0.01 for MBS. There were some small differences between the breed groups in the heritability estimates. The genetic correlations between FT and MBS were negative (favourable) and consistent across the datasets (–0.47 ± 0.12, combined analysis). The genetic correlations between IBT and MBS were positive (favourable) but not significant (0.12 ± 0.11, combined analysis). The genetic correlations between IBT and FT were also favourable, but small and generally not significant. There were small favourable genetic correlations between MBS and various bodyweights (–0.17 ± 0.07, yearling) and NLW (–0.25 ± 0.07). However, there were no significant genetic relationships between the temperament and production traits. The moderate heritability and repeatability of MBS indicate maternal behaviour could be improved by selection, and that it could be a useful additional trait in breeding programs for improved reproduction.
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Walkom, S. F., e D. J. Brown. "Impact of liveweight, fat and muscle sire breeding values on ewe reproduction is minimal but variable across Australian grazing systems". Animal Production Science 57, n. 9 (2017): 1952. http://dx.doi.org/10.1071/an15574.
Testo completoAbstract (sommario):
Australian sheep producers have the potential to improve reproductive rates through optimising ewe body condition across the production cycle. Managing ewe body condition can become costly when supplementary feeding is required due to poor pasture growth or rainfall and by using appropriate genetics, producers can theoretically reduce the flock’s dependency on supplementary feed and improve reproductive rates. Reproductive records from the Information Nucleus Flock and Sheep Genetics Merino and maternal breed datasets were analysed to examine the influence of sire breeding values for liveweight (post-weaning, yearling and adult assessments), fat and eye muscle depths (post-weaning and yearling assessments) and number of lambs weaned on reproductive performance (fertility, litter size and number of lambs born) across a variety of production environments. To determine the impact of environmental conditions on the relationship between weight, ultrasound body composition, and reproduction traits the daughters’ adjusted reproductive performances were regressed on the sire’s breeding value across flocks, within flocks and within flock × year. Irrespective of age at assessment, sire breeding values for liveweight, fat and eye muscle depths had very little association with the reproductive performance of their daughters, on average. The regressions of reproduction on weight, and fat and eye muscle depth traits varied across flocks from unfavourable to favourable estimates. The very small overall impact of weight, and fat and eye muscle depth traits, on average suggests that using sire breeding values for number of lambs weaned, which had a large impact on reproduction, will provide the most viable method to genetically improve reproductive performance within the production system in question.
38
Cloete, S. W. P., J. C. Greeff e R. P. Lewer. "Heritability estimates and genetic and phenotypic correlations of lamb production parameters with hogget liveweight and fleece traits in Western Australian Merino sheep". Australian Journal of Agricultural Research 53, n. 3 (2002): 281. http://dx.doi.org/10.1071/ar00183.
Testo completoAbstract (sommario):
Heritability estimates (h2) for weight of lamb weaned and number of lambs weaned totalled over 3 reproduction opportunities were estimated in a multi-bloodline Western Australian medium wool resource flock. These traits were defined to give an indication of lifetime lamb production (the ewes were retained in the breeding flock for a maximum of 4 lambing opportunities). Both reproduction traits were highly variable, as suggested by coefficients of variation of approximately 50%. The between-bloodline variance ratio was significant (P < 0.05), but failed to exceed 5% of the total across-bloodline phenotypic variation. Within-bloodline h2 ( s.e.) was estimated at 0.154 0.040 for total weight of lamb weaned, and at 0.141 0.040 for total number of lambs weaned. Within-bloodline genetic correlations of both traits with hogget liveweight were positive and significant (P < 0.05; 0.58 0.11 and 0.26 0.13, respectively). Within-bloodline genetic correlations of the reproduction traits with wool production were generally positive, being 0.26 0.11 for the correlation between total weight of lamb weaned and clean fleece weight, and 0.29 0.15 for the correlation between total number of lambs weaned and clean fleece weight. Clean yield was genetically unrelated to both measures of reproductivity. The genetic correlation of total weight of lamb weaned per breeding ewe with fibre diameter was positive in sign, but smaller than twice its standard error (0.17 0.10). The corresponding estimate for total number of lambs weaned was 0.16 0.12. It was concluded that the reproduction traits investigated would respond to selection in Western Australian Merinos if it should form part of a breeding strategy. Genetic correlations with hogget liveweight and wool traits were generally favourable.
39
Cottle, DJ. "The derivation of economic values in breeding programs for Australian Merino sheep with changing wool prices and flock production averages". Australian Journal of Agricultural Research 41, n. 4 (1990): 769. http://dx.doi.org/10.1071/ar9900769.
Testo completoAbstract (sommario):
The impact of fluctuating wool prices on setting economic values (EVs) in selection indices, e.g. WOOLPLAN, are studied by modelling genetic change in a flock following index selection, Operating under different wool price regimes. Because future price changes are difficult to predict, there is no guaranteed, optimal method of determining EVs. One possibility is the use of a moving regression of the last five years' wool prices (in real terms), rather than setting the index once, or every five years, or every year, based on current prices. The ratio (R) of clean wool price to micron premium is more important than actual prices. It is suggested that the default EVs used currently in WOOLPLAN are appropriate for strong wool Merino flocks. The choice and implications of EVs in other situations are discussed.
40
Khamiruev, T. N. "THE USE OF IMMUNOGENIC MARKERS IN THE SELECTION OF SHEEP OF ZABAIKALSKAYA BREED". Siberian Herald of Agricultural Science 48, n. 4 (23 ottobre 2018): 87–93. http://dx.doi.org/10.26898/0370-8799-2018-4-12.
Testo completoAbstract (sommario):
The article presents the results of immunogenic certification of fine-fleece sheep of Zabaikalskaya breed of the Khangil type, bred by a sophisticated reproductive cross-breeding method with Australian and Manych Merino breeds. The animals are adapted to a year-round grazing in harsh climatic conditions. The study was carried out in the pedigree plant of Trans-Baikal Territory. The immunogenic certification of animals was carried out in the laboratory of the immunogenic appraisal by six systems of blood groups including 14 antigenic factors. The blood group characteristics of the young were determined depending on their origin. Progeny of Zabaikalskaya stud ram breed of Khangil type is characterized by the highest frequency of occurrence of antigenic factors Aa, Bd, Bi, Bg, Cb, Ma, Mb, R. Given this, the progeny that was bred revealed similarities in the antigenic factors Bd, Bi, Ca, Cb, Ma and R, whereas the discrepancy was established for the antigens Aa, Ab, Bb, Be, Bg, Mb and O. The degree of the genetic similarity and genetic distance between animals within the breed amounted to 0.920 and 0.083 respectively. It is probable that high incidence of antigens Ma, Aa and Bd with the sheep of Zabaikalskaya breed of Khangil type corresponds to their mutton-wool production type. The work demonstrates necessity of the use of genetic markers in the breeding process and in the objective assessment of the degree of genetic similarity and genetic distance between animals of different origin within one breed.
41
Hrymak, K. "The sexual activity of the ram-sires, depending on their mode of use". Scientific Messenger of LNU of Veterinary Medicine and Biotechnologies 21, n. 91 (6 novembre 2019): 29–32. http://dx.doi.org/10.32718/nvlvet-a9105.
Testo completoAbstract (sommario):
Literary data are presented and their analysis is conducted regarding the mode of use of ram-sires and their effect on sexual activity and sperm productivity. The results of research of scientists with recommendations of optimal modes of use of fetuses for semen production and its cryopreservation in non-pairing and steaming periods are presented. According to the results of the analysis of many researchers, the activity of the sexual reflexes of the rams in the spring and summer decreases by 1.4 times compared to the winter. At the same time quantitative indicators of sperm productivity decrease. However, M.M. Aibazov (1987) experimentally confirmed that sheep-breeders of the Caucasian fine-breed and Australian merenos breed exhibit high sexual activity and produce sperm of satisfactory quality in all seasons. Similar results were obtained by British researchers in the study of sexual activity and sperm productivity of ram-sires of British breeds. A.A. Ivanov (1987) indicates the regime of use of ram sires, for five years with obtaining and subsequent freezing in the unpaired period 6 ejaculates (2 doublets 3 times) per week and in the breeding season 10 ejaculates (2 doublets 5 times) week. P.P. Kundyshev (2004) considers it possible and proposes to obtain from the breeding rams for cryopreservation and storage during the year, both unpaired and steaming periods, with daily ejaculate production. This mode, according to the author, provides a sufficiently high fertility sperm up to 50.3 percent. In the study of sexual activity and sperm productivity of ram-sires of different breeds, including the North Caucasian meat-wool, jalgin merino, Soviet merino, maniche merino, Russian meat merino, Edelbaev, polldore P.P. Mammoth and others. (2018) found that the most active were the rams of the Edinburgh breed, which took 22 seconds. ejaculate secretion, and the slowest texel breeders, which took 39 seconds to ejaculate. The rams of the other breeds listed above spent 25 to 34 seconds to ejaculate. In addition, rams of Texel breed produced the lowest activity sperm, and therefore only 19 sperm were frozen from one ejaculate, with an average of 20 to 26 sperm species tested.
42
Mortimer, S. I., D. L. Robinson, K. D. Atkins, F. D. Brien, A. A. Swan, P. J. Taylor e N. M. Fogarty. "Genetic parameters for visually assessed traits and their relationships to wool production and liveweight in Australian Merino sheep". Animal Production Science 49, n. 1 (2009): 32. http://dx.doi.org/10.1071/ea08074.
Testo completoAbstract (sommario):
Heritability was estimated for a range of visually assessed traits recorded on Merino sheep, together with the phenotypic and genetic correlations among the visually assessed traits and correlations of the visually assessed traits with measured wool production traits and liveweight. Data were derived from four research resource flocks, with a range of 12 958 to 57 128 records from animals with 478 to 1491 sires for the various traits. The estimates of heritability were high for the wool quality traits of handle, wool character and wool colour (0.33–0.34) and the conformation traits of face cover, neck wrinkle and body wrinkle (0.42–0.45), moderate for front leg structure (0.18) and low for back leg structure (0.13). Fleece rot score had low heritability (0.14), while classer grade was moderately heritable (0.20). Estimates of genetic correlations among the visually assessed wool quality traits were low to moderate in size and positive (0.17–0.47). Genetic correlation estimates among the assessed conformation traits were generally very low, except for the genetic correlations between scores for neck and body wrinkle (0.92 ± 0.01) and front and back leg structure (0.31 ± 0.09). Fleece rot score had low positive genetic correlations with neck and body wrinkle scores (0.18 ± 0.05 and 0.15 ± 0.05, respectively) and classer grade (0.26 ± 0.06). Classer grade was slightly positively correlated with the wool quality traits (0.17–0.45) and leg structure traits (0.21–0.25). The genetic correlations among the visually assessed traits were generally neutral to favourable. The visually assessed wool quality traits had low to moderate favourable genetic correlations with mean and coefficient of variation of fibre diameter (0.19 –0.47), but negative correlations with clean wool yield (–0.26 to –0.37). Face cover was unfavourably correlated with staple length (–0.27 ± 0.04) and liveweight (–0.23 ± 0.02). Neck and body wrinkle scores were genetically associated with higher greasy (0.33–0.39) and clean fleece weights (0.19–0.22), greater coefficient of variation of fibre diameter (0.24–0.26) and fibre curvature (0.27–0.28), but with reduced yield (–0.26 to –0.28) and staple length (–0.34 to –0.41). Fleece rot score was genetically correlated with clean fleece weight (0.26 ± 0.05) and coefficient of variation of fibre diameter (0.27 ± 0.04). Classer grade was favourably correlated with greasy and clean fleece weights (–0.41 to –0.43), staple length (–0.29 ± 0.04), liveweight (–0.36 ± 0.03) and coefficient of variation of fibre diameter (0.27 ± 0.03). Most genetic correlations between the visually assessed traits and the measured production traits and liveweight were close to zero and less than 0.2 in magnitude. This study provides accurate values for the parameter matrix required to incorporate visually assessed traits into breeding objectives and the genetic evaluation programs used in the Australian sheep industry, allowing the development of breeding objectives and indexes that optimally combine visually assessed performance and measured production in Merino sheep.
43
Hollema, Baukje L., Piter Bijma e Julius H. J. van der Werf. "Sensitivity of the breeding values for growth rate and worm egg count to environmental worm burden in Australian Merino sheep". Journal of Animal Breeding and Genetics 135, n. 5 (11 luglio 2018): 357–65. http://dx.doi.org/10.1111/jbg.12349.
Testo completo
44
Cloete, S. W. P., J. C. Greeff e R. P. Lewer. "Direct and maternal genetic (co)variances for hogget liveweight and fleece traits in Western Australian Merino sheep". Australian Journal of Agricultural Research 53, n. 3 (2002): 271. http://dx.doi.org/10.1071/ar00184.
Testo completoAbstract (sommario):
(Co)variance estimates for hogget liveweight, greasy fleece weight, clean fleece weight, clean yield, fibre diameter, and the coefficient of variation of fibre diameter were obtained for a Western Australian Merino resource flock. The flock encompassed 16 medium wool bloodlines and data were available for the period 1982–93. Direct additive genetic variances (h2) — expressed as a ratio of the total phenotypic variance within bloodlines — were estimated at 0.52 for hogget liveweight, 0.44 for greasy fleece weight, 0.42 for clean fleece weight, 0.63 for clean yield, 0.71 for fibre diameter, and 0.62 for coefficient of variation of fibre diameter. Maternal genetic variance estimates were significant (P < 0.05) only in hogget liveweight and fibre diameter, but components within bloodlines were low (0.05 for liveweight and 0.02 for fibre diameter). Direct within-bloodline genetic correlations of hogget liveweight as well as greasy and clean fleece weight with fibre diameter were positive (0.17, 0.31, and 0.31, respectively), suggesting that selection for bigger and heavier cutting sheep would generally lead to a broader fibre diameter. Liveweight was unrelated to clean yield and negatively related to coefficient of variation of fibre diameter (–0.17). Greasy fleece weight was negatively related to clean yield (–0.20). The genetic correlation of clean fleece weight with clean yield was positive (0.37). Wool quantity was, in general, positively related to coefficient of variation of fibre diameter, although the estimated genetic correlations were low (0.12 for greasy fleece weight and 0.07 for clean fleece weight). The genetic correlation between fibre diameter and coefficient of variation of fibre diameter was negative, and fairly low (–0.10). These results are discussed with reference to sheep breeding.
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Brown, D. J., A. A. Swan e J. S. Gill. "Within- and across-flock genetic relationships for breech flystrike resistance indicator traits". Animal Production Science 50, n. 12 (2010): 1060. http://dx.doi.org/10.1071/an10102.
Testo completoAbstract (sommario):
Flystrike is a major cost for the Australian sheep industry. The industry is currently implementing selection strategies for flystrike resistance to reduce the need for breech flystrike prevention. The following indicator traits are used to select for breech flystrike resistance: wool cover, skin wrinkle on the body and breech, scouring (dags) and wool colour. The aims of this study were to estimate genetic correlations between these indicator traits and production traits using the Sheep Genetics database, to distinguish between within- and across-flock genetic relationships, and to quantify responses to selection using indexes that include breech wrinkle as a proxy trait for flystrike resistance. Breech flystrike indicator traits are all heritable; however, there are significant antagonisms between wrinkle score and some production traits, primarily fleece weight and fibre diameter. Thus, simultaneous improvement in both flystrike resistance and production will be most efficient when index selection is used. Our results show that, depending on the level of emphasis placed on breech wrinkle in the index, reductions in breech wrinkle score of 0.4–0.9 units can be achieved over a 10-year period. As across-flock relationships are generally stronger than within-flock relationships, breeders will be able to take advantage of this additional variation, depending on the relative merit of their flocks. Therefore, ram breeders should combine within-flock selection with across-flock selection where possible. Sheep Genetics released early breech wrinkle Australian Sheep Breeding Values in September 2009 to assist Merino breeders in making faster progress towards reducing breech wrinkle by using flock selection.
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Paganoni, B. L., M. B. Ferguson, S. Fierro, C. Jones, G. A. Kearney, P. R. Kenyon, C. Macleay, C. Vinoles e A. N. Thompson. "Early reproductive losses are a major factor contributing to the poor reproductive performance of Merino ewe lambs mated at 8–10 months of age". Animal Production Science 54, n. 6 (2014): 762. http://dx.doi.org/10.1071/an13240.
Testo completoAbstract (sommario):
The reproductive performance of Merino ewe lambs is lower than that achieved by mature ewes and is highly variable. It is likely that embryo loss represents a major source of reproductive wastage in Merino ewe lambs, but to our knowledge no studies have attempted to determine when the major reproductive losses occur or identify predisposing factors that are likely to lead to high rates of pregnancy failures in ewe lambs. After characterising where reproductive losses occurred in Merino ewe lambs mated at 8–10 months of age, we tested the hypothesis that pregnancy failure in ewe lambs is influenced by nutrition and liveweight change around conception and the genetic potential for growth of the ewe lamb. Two-hundred and twenty-four Merino ewe lambs born from 10 sires with Australian Sheep Breeding Values were teased for 14 days using vasectomised rams, and then fed two different diets for 68 days during mating. All ewe lambs were weighed and the appearance of crayon marks on their rump was recorded most days. Blood samples for progesterone assay were collected on Days 5, 12 and 17 after the first record of a crayon mark. Ultrasonography using a trans-rectal probe was used to measure the number of corpora lutea present, as a proxy for ovulation rate, 9 days after the first record of a crayon mark during the mating period. A further trans-rectal ultrasonography was undertaken 30 days after marking from the entire ram to determine pregnancy status and count the number of embryos. Over the entire mating period 54% of ewe lambs were pregnant with 66 fetuses per 100 ewes mated. The average ovulation rate was 150% however up to 84% of this potential was lost by weaning and the major contributor to this apparent deficit was the loss that occurred during the first 17 days after mating. Pregnancy failure was not significantly related to nutrition or liveweight change during mating however, there were significant differences in pregnancy failure between different sire groups. Pregnancy failure was significantly less for ewe lambs from sires with higher breeding values for weight and fat at post-weaning age (8–10 months). Only 60% of ewe lambs had achieved puberty when rams were introduced and only 83% by 35 days after mating. In addition, almost half of the ewe lambs that were mated for the first time during the first 35 days after rams were introduced, but failed to get pregnant, then seemed to skip a cycle or did not cycle again before the end of the 68-day mating period. Liveweight at introduction of entire rams was positively related to fertility, ovulation rate and reproductive rate. This study confirms that selection of sires with higher breeding values for post-weaning weight and fat will increase the fertility and reproductive rate of Merino ewe lambs mated at 8–10 months. This response is due in part to enhancing the onset of puberty and increasing the proportion of ewe lambs cycling at the start of mating and reducing pregnancy failure.
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Young, J. M., A. N. Thompson, M. Curnow e C. M. Oldham. "Whole-farm profit and the optimum maternal liveweight profile of Merino ewe flocks lambing in winter and spring are influenced by the effects of ewe nutrition on the progeny's survival and lifetime wool production". Animal Production Science 51, n. 9 (2011): 821. http://dx.doi.org/10.1071/an10078.
Testo completoAbstract (sommario):
Profitability of sheep production systems in southern Australia is optimised at a stocking rate that provides adequate nutrition for breeding ewes and enables efficient utilisation of grown pasture and supplements. In this paper we used bio-economic modelling to develop optimum liveweight1 profiles for spring-lambing Merino ewes in different environments. The modelling included the impacts of the ewe liveweight profile on the production of the ewe and the survival and lifetime wool production of her progeny. Fifteen ewe liveweight profiles were analysed for each region to determine the profitability of varying ewe liveweight at joining, varying rate of loss of liveweight after joining and the rate of gain in liveweight from the minimum to lambing. The analyses support the hypotheses that whole-farm profitability is sensitive to the liveweight profile of Merino ewe flocks and that there is a liveweight profile that maximises whole-farm profit. The variation between the most and least profitable ewe liveweight profile was $69 0002 per farm ($14.30/ewe) for south-west Victoria, $51 000 per farm ($8.70/ewe) for Great Southern Western Australia and $33 300 per farm ($9.70/ewe) for southern New South Wales. The changes in profit were due to differences in costs of feeding to achieve the ewe liveweight profile and its influence on the production of both the ewes and their progeny. Failure to include the impacts of liveweight profile on progeny survival and lifetime wool production incorrectly identifies the optimum ewe liveweight profile and provided inaccurate estimates of profitability. The optimum liveweight profiles for ewes lambing in spring were similar for all three regions and insensitive to changing commodity prices, pasture productivity and management. The optimum profile was to join ewes at ~90% of the standard reference weight of the genotype, lose a small amount of weight after joining and regain weight in late pregnancy to return to the joining weight by lambing. Regaining the liveweight lost in early pregnancy by lambing is the most important target to achieve. The cost per farm of missing this liveweight target by 1 kg was $13 000 ($2.60/ewe) for south-west Victoria, $8900 ($1.45/ewe) for Great Southern Western Australia and $5500 ($1.65/ewe) for southern New South Wales. By contrast, the cost per farm of missing the joining target by 1 kg was $5500 for south-west Victoria and less than $2000 across the other two regions. Whole-farm profit increased with increasing stocking rate up to an optimum and regardless of stocking rate there is an additional opportunity to increase whole-farm profit by up to 15% by managing ewes to achieve the optimum liveweight profile. This indicates that the optimum liveweight profile should be achieved by increasing the level of grain feeding and altering the timing of utilising the farm feed resources rather than manipulating stocking rate.
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Gonzalez, R. E., D. Labuonora e A. J. E. Russel. "The effects of ewe live weight and body condition score around mating on production from four sheep breeds in extensive grazing systems in Uruguay". Animal Science 64, n. 1 (febbraio 1997): 139–45. http://dx.doi.org/10.1017/s1357729800015642.
Testo completoAbstract (sommario):
AbstractEwe live iveights were recorded 4 weeks prior to mating, at the beginning of mating and 22 to 23 days later over a period of 3 years in a flock of some 300 breeding ewes comprising approximately equal numbers of Australian Merino, Ideal (Polwarth), Merilin and Corriedale breeds in a pastorally based grazing system in Uruguay. Multiple-bearing ewes were generally heavier than single-bearing ewes which in turn were heavier than ewes which did not conceive, these differences being greatest in 3- and 4-year-old ewes (i.e. in their second and third breeding seasons). Body condition scores of non-pregnant ewes were lower than those of pregnant ewes, particularly in the 3-and 4-year-old age groups. Ewe live weights achieved prior to, during and at the end of the mating period and the body condition score achieved 4 weeks prior to mating all had significant influences on the number of lambs born (P < 0·01) but there were no significant effects of changes in either live weight or body condition over the 4 weeks prior to mating or during the mating period. The effect of body condition score over the range from 2·0 to 4·0 was to increase the proportions of single- and multiple-bearing ewes and to decrease the proportion of non-pregnant ewes such that the number of lambs born per ewe mated increased from 0·94 to 1·38. Fleece weights differed significantly between breeds, Corriedales having the heaviest fleeces and Merilins the lightest (4·26 and 3·22 kg respectively). Wool production was also significantly and positively affected by age (P < 0·01) and by ewe weight at mating (P < 0·01). The results demonstrate the importance of giving preferential nutritional treatment to younger ewes to ensure a satisfactory subsequent lambing performance and improved wool production.
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Allingham, P. G., W. Barris, A. Reverter, V. Hilsenstein, R. van de Ven e D. L. Hopkins. "Sire and growth-path effects on sheep meat production. 3. Fascicular structure of lamb loin muscle (m. longissimus lumborum) and the impact on eating quality". Animal Production Science 49, n. 3 (2009): 239. http://dx.doi.org/10.1071/ea08163.
Testo completoAbstract (sommario):
The effects of sire genetics and growth path on the fascicular structure (FS) of lamb loin muscle (m. longissimus lumborum; LL) and the consequences for eating quality were studied in progeny (n = 299) of 20 Poll Dorset sires and Merino ewes. Sires were selected on the basis of their Australian sheep breeding values (ASBV) for post-weaning growth (PWWT), loin eye muscle depth (PEMD) and subcutaneous fat (PFAT). Growth of lambs was varied by time of weaning (early or late) and by feeding level within weaning group, where lambs were either fully fed throughout or were feed restricted for 55 days then re-alimented to achieve liveweight of ~45 kg at slaughter. The FS variables were determined in differentially stained histological sections of LL by using automated image segmentation and circle geometry methodology and were defined as percentage connective tissue, perimysial seam thickness and fascicular width. Sire ASBV was not a significant covariate to measures of FS, despite ASBV-related effects on growth, carcass leanness and fatness. Independent of weaning time, faster growth was induced by re-alimentation of feed-restricted lambs, resulting in LL with less connective tissue as a percentage of cross-sectional area and larger fascicles than for fully fed peers. The direction of the perimysial seam thickness response varied with treatment and time of weaning. Rapid growth of re-alimented early weaned restricted lambs resulted in thinner seams than for fully fed peers, whereas the opposite response was observed in the late-weaned lamb contrast. This suggests that the weight and age of the lamb at the time of nutritional compromise and re-alimentation are important factors in determining the thickness of perimysial connective-tissue seams. Whilst the evidence confirms differential accretion of the myofibrillar and connective tissues and despite reports of positive effects on tenderness brought about by such changes, variation in structural measures was not associated with variation in either objective measures (compression) or sensory scores for tenderness of the loin muscle. The data from the present study support the tenet that rapid growth before slaughter, combined with appropriate sire genetics, will not compromise the physical characteristics and sensory qualities of the meat.
50
Torekhanov, A. A., e N. K. Zhumadillayev. "ETTI MERINOS – KAZAKHSTANI EXPORT-ORIENTED MEAT BREAD". REPORTS 335, n. 1 (12 febbraio 2021): 146–51. http://dx.doi.org/10.32014/2021.2518-1483.21.
Testo completoAbstract (sommario):
Sheep breeding in Kazakhstan is a traditional branch of animal husbandry. The development of the industry is facilitated by the presence of large areas of pasture lands, as well as the existing valuable gene pool of breed resources, created by national selection and long-term work of scientists-breeders. The republic has great potential for the further development of sheep breeding industry and is able not only to meet the population's need for mutton, but also to become a major exporter. The restoration and further development of domestic sheep breeding should be based on rational use of genetic potential of animals and natural pastures of the country for the cost-effective production of high quality sheep products that meet international standards. The article deals with the development of fine-wool sheep breeding in Almaty, Zhambyl and South Kazakhstan regions, improvement of meat characteristics of the South Kazakh merino. The experience of using "etti merino" rams-producers in farms of Turkestan region showed that meat merino rams have a positive effect on meat productivity of the South Kazakh merino, and at the same time do not worsen their wool characteristics. The information on the population number of sheep of "Etti Merino" breed for 2020, the class composition of the ewes on farms, productivity of rams-producers in a number of generations, assessment of the quality of the offspring of 6-7 month old rams, wool productivity of the breeding groups of female sheep are presented.