Tesi sul tema "Sheep Reproduction"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Sheep Reproduction.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Sheep Reproduction".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Nassiri, Mohammad Taghi Beigi. "Aspects of prolificacy in Cambridge sheep". Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321435.
2
Ibraheem, Majid. "The manipulation of seasonality of reproduction in sheep". Thesis, University of Aberdeen, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332379.
Abstract (sommario):
The phenomenon of seasonability of reproduction restricts the ewe to only one lambing around the same time every year, which in turn prevents an even supply of lamb meat to the market. The long term objective of the current study was to develop two systems of early and summer lambing using alternative techniques for the manipulation of sheep production in an attempt to produce high quality lamb throughout the year. In recent years, major advances in our knowledge of seasonality of reproduction have been the recognition of the integral role of the pineal gland and its indoleamine melatonin in the timing of reproductive activity and the use of the pattern of reproductive behaviour in sheep in the manipulation of reproductive processes. Therefore, the current study aimed at examining the use of melatonin and/or the 'ram effect' in early and summer lambing systems in order to report on their effectiveness in advancing the breeding season and/or enhancing fecundity. Also, the concern over the seasonal variation in libido and semen quality in the ram made it necessary to examine ways of eliminating the seasonal depression in the mating performance and capcity of the ram. Experiments 1, 2 and 3 examined the effectiveness of the intraruminal device of melatonin administration and/or the 'ram effect' in advancing the breeding season of the ewes. Also the effects of duration and methods of 'teasing' were assessed.
3
Archer, Zoe Anne. "Neuroendocrine control of appetite and reproduction in sheep". Thesis, University of Aberdeen, 2001. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602029.
Abstract (sommario):
Reproductive neuroendocrine activity and appetite are modulated at the hypothalamus by both nutritional status and photoperiod in the seasonal animal. The objectives of this work were (1) to measure circulating hormones and/or metabolites that relay information about peripheral nutritional status to the hypothalamus, (2) to identify which hypothalamic neuropeptides and receptors that are responsive to photoperiodic and nutritional feedback and (3) to establish which changes in peripheral signals and/or hypothalamic neuropeptides are associated with alterations in the activity of the reproductive neuroendocrine axis. Three main experiments were carried out. The first experiment (Chapter 1) utilised a 2 x 2 design to examine the separate and interactive effects of photoperiod and food restriction on hypothalamic neuropeptide and receptor mRNA expression and on GnRH/LH secretion. In the second experiment (Chapter 2), two components of nutritional status, BC and increased food intake were investigated since both are positively related to reproductive performance in sheep. In the final experiment (Chapter 3) the approach was to use an exogenous treatment to artificially raise plasma insulin in an attempt to "drive" some of the foregoing effects. Collectively these studies have lead to the first localisation AgRp, MCH, orexin, Mc3R, Mc4R gene expression in the ovine hypothalamus. They indicate that circulating insulin and leptin are major factors relaying information about nutritional status to the hypothalamus. In addition, they have dissociated BC and food intake as signals to the hypothalamus. Moreover these studies have provided no evidence that NPY, AgRp, POMC, MCH and ObRb play a role in driving seasonal changes in appetite and gonadotrophin secretion. However they do suggest NPY-ergic and melanocortin pathways are important in maintaining appetite/bodyweight/energy homeostasis or restoring energy balance following perturbation. Furthermore the results show that changes in nutrient-sensitive hypothalamic neuropeptide and receptor gene expression may not necessarily lead to alterations in the activity of the reproductive neuroendocrine axis. However, they do indicate that increased NPY biosynthesis during food restriction may be involved in the inhibition of pulsatile GnRH/LH release.
4
Singh, Inderjeet. "Embryonic survival in adrenal hyperactivity in sheep". Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386839.
5
Ferasyi, Teuku Reza. "Mathematical model of the reproductive endocrine system in male sheep". University of Western Australia. School of Animal Biology, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0080.
Abstract (sommario):
[Truncated abstract] The activity of the reproductive endocrine axis is the result of interactions among many organs and tissues, particularly the hypothalamus, pituitary gland and gonad. However, it depends on more than the communication between anatomical structures because it is also affected by genotype, internal factors (e.g., metabolic inputs) and external factors (e.g., photoperiod, socio-sexual cues, stress, nutrition). This multifactorial complexity makes it difficult to use animal experimentation to investigate the pathways and mechanisms involved. Therefore, in this study, I have turned to mathematical modelling. The general hypothesis was that, by modelling the hormonal feedback loop that links the hypothalamus, pituitary gland and gonad, I would be able to discover the critical control points in this homeostatic system. This would allow me to inform and direct research into the processes that control reproduction, including inputs from environmental factors. My studies began with the development of a model of the negative feedback loop through which testosterone controls the secretion of pulses of gonadotrophin-releasing hormone (GnRH) by the hypothalamus. The model incorporated two critical factors: testosterone concentration and a time delay in the inhibition of the activity of the GnRH 'pulse generator' by testosterone. The general assumptions were: i) there are two positive feedforward processes (GnRH pulses stimulate LH pulses, and, in turn, LH pulses stimulate testosterone secretion); ii) testosterone exerts negative feedback that reduces the frequency of GnRH pulses. The model incorporated a group of equations that represent the GnRH pulse generator, through which the inhibitory effect of testosterone acted to reduce GnRH pulse frequency. Simulations were run with various values for the time delay in feedback and, as model development progressed, the simulations were extended to include combinations of time delays and levels of sensitivity of the GnRH pulse generator to inhibition by testosterone. The output of the simulations showed clearly that a time delay in negative feedback, as well as the concentration of testosterone, can greatly affect the frequency of GnRH pulses and the shape of the GnRH secretory profile. Importantly, the effect of the time delay depends on the sensitivity of the pulse generator to testosterone. In addition, the simulations suggested two additional components that might be involved in the control of the GnRH pulse generator: i) a delay in the rate of adaptation to a change in steroid feedback; and ii) a minimum pulse interval (maximum frequency). These studies iii therefore suggest that the regulation of the activity of the GnRH pulse generator, and thus the frequency and profile of GnRH and LH pulses, requires interactions among these four components. These interactions should be tested in animal experimentation. In the next stage, I extended the model so I could test whether the feedback delay might involve the process of aromatization in which testosterone is converted to oestradiol at brain level. ... This information can be used to direct future experimental studies that will help us to understand the factors that underlie the dynamic behaviour of the hypothalamic and pituitary systems that control reproduction.
6
Holmberg, Bradford J. "Influence of the vagus nerve and urocortin on the nutrition-reproduction axis of the ovine /". free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074407.
7
Tempest, Louisa-Jayne. "Parasites and the costs of reproduction in Soay sheep". Thesis, University of Stirling, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720356.
8
Hawken, Penelope Alison Rhian. "The role of socio-sexual cues in sheep reproduction". Thesis, University of Newcastle Upon Tyne, 2006. http://hdl.handle.net/10443/1660.
Abstract (sommario):
Exposure of previously isolated anoestrous ewes to a ram induces an almost instantaneous rise in luteinising hormone (LH) pulse frequency. This physiological response, a phenomenon coined 'the ram effect' is commonly sufficient to override the seasonal suppression of the hypothalamic-pituitary axis and induce a synchronous first ovulation. The objective of the first series of experiments in this thesis was to develop a nonpharmacological method of oestrus synchronisation, using socio-sexual cues, for natural mating of mule ewes during the breeding season. Initially two experiments were conducted to investigate the effect of short-term fence line and vasectomised ram exposure repeated every 17 days on three occasions during the transition into the breeding season. Ewes repeatedly exposed to the ram had a significantly compacted mating period compared to ewes maintained in isolation from rams prior to mating. This compaction persisted through to lambing with no significant negative effect on litter size. Artificially inseminated ewes synchronised using the above method of ram synchronisation had higher conception rates than progestagen synchronised ewes. The second objective was to compare the efficacy of different durations and frequencies of ram exposures as methods of oestrus synchronisation. Ewes maintained continuously with rams over the pre-mating period had a more compacted mating and lambing period than ewes exposed intermittently to rams. Maiden ewes typically show a poorer level of reproductive competence than adult ewes. Similarly maiden ewes induced to ovulate using the ram effect have been found to have a lower ovulatory response. The next objective of this thesis was to determine if pre-exposure to the ram during anoestrus or the breeding season would modulate the hormonal and behavioural responses of maiden ewes when re-introduced to rams during the breeding season or anoestrus. There was no major effect of prior experience of the ram on any parameters of the LH response to ram introduction. However ewes with prior ram experience did have more positive interactions with the rams and demonstrated more ram seeking behaviour. Incorporation of socio-sexual cues with artificial methods of reproductive control has to date been restricted to ram exposure post progestagen sponge withdrawal. Therefore the final objective of this thesis was to investigate the effect of ram exposure towards the end of a progestagen synchronisation protocol on ewe fertility. There was no significant difference in conception rates between ram exposed and control ewes, however ram exposed ewes had a significant depression in mean litter size due to a greater number of ewes having single lambs. The studies in this thesis show a robust and repeatable endocrine response to ram introduction in mule ewes exposed to the ram during the transition between anoestrus and the breeding season. The potency of the socio-sexual cues from the ram permits modification of the distribution of oestrus within randomly cycling ewes. The findings in this thesis highlight the potential for application and development of pre-mating strategies using socio-sexual cues within seasonal breeds of sheep.
9
Bancroft, David. "Genetic variation and fitness in Soay sheep". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338112.
10
Fray, Martin Dennerley. "Gonadotrophin release in post parturient cattle and sheep". Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314751.
11
Moore, Céline. "Genetic influence on predictability of reproductive potential of rams". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65523.
12
Pickard, R. M. "The role of omega-3 fatty acids in sheep reproduction". Thesis, University of Newcastle Upon Tyne, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433539.
13
Zhang, Song. "Peripheral and central pathways linking metabolic status and reproduction in male sheep". University of Western Australia. School of Animal Biology, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0037.
Abstract (sommario):
[Truncated abstract] Reproductive activity is affected by external factors such as photoperiod, social cues, stress and nutrition, all of which can alter the pulsatile activity of the GnRH neurons, which is the major neuroendocrine system used by the brain to control gonadal function. In the male Merino sheep, nutrition is one of the most powerful factors that affect pulsatile LH secretion, used commonly to bioassay GnRH neuronal activity. More accurately, the reproductive system responds to “metabolic status”, rather than “nutrition”, and the three factors that contribute to metabolic status are food intake, the amount of body reserves and the rate of energy expenditure ... In this thesis, I tested the general hypothesis that the metabolic hormones and hypothalamic neuropeptides that are known to control food intake also mediate the effect of metabolic status on the activity of the GnRH neurons ... In conclusion, the results from my experiments provide some insight into the mechanisms by which metabolic status affects reproductive activity in male sheep. Plasma insulin, which changes with alterations in metabolic status, appears to play a critical role in the regulation of GnRH neuronal activity. The level of leptin seems to have a permissive role only in lean animals. Orexins acting via OX2 receptors could be involved in the activation of reproductive function following an acute increase in nutrition. However, the neuropeptidergic systems can not be ruled out because they might be involved in very early steps of responses to nutrition.
14
Hughes, Michelle Ann. "Molecular analysis of ovulation rate in the Cambridge ewe". Thesis, Bangor University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295279.
15
Audicana, Lina. "Cervical ripening with PGEâ†2 for transcervical embryo transfer in sheep : studies of EPâ†3 receptor mRNA". Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241745.
16
Melnyk, Peter M. (Peter Michael). "Estrogen regulation of testicular function in the adult ram". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59414.
Abstract (sommario):
During the nonbreeding season (July), three groups of five Dorset x Leicester x Suffolk rams were assessed over a period of 5 days. One group of rams (control) was implanted (sc) with five 5cm empty Silastic capsules (i.d. 3.4mm, o.d. 4.6mm); two other groups, designated as Low-E$ sb2$ and High-E$ sb2$, received five estradiol filled capsules of either 5cm or 10cm, respectively for 4 days. Estradiol treatment elevated serum estradiol concentration about 150% in the Low-E$ sb2$ groups (15.7 $ pm$ 1.3 pg/ml) and 300% in the High-E$ sb2$ groups (26.6 $ pm$ 2.4 pg/ml) compared with controls (6.3 $ pm$ 0.8 pg/ml). In the absence of LH pulsing, mean LH, FSH and testosterone concentrations were all decreased significantly (P $<$.05) with increasing estradiol concentration, while PRL concentration was increased (P $<$.05) by as much as 105%. In the LH-pulsed groups, LH-peak height on day 4 was comparable for all three groups of rams and peak frequency was, as expected, consistently increased to 4 peaks per 6 hours. The increase in mean testosterone concentration (P $<$.05) in all three groups was due to an increase in testosterone baseline concentration and testosterone peak frequency.
17
Lewis, Ronald Martin. "Reproductive performance of dorset ewes in the star accelerated lambing system". Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-08252008-162636/.
18
Yarney, Thaddeus A. "Sexual maturational changes in the pituitary and testes of ram lambs and predictability of adult reproductive function". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72049.
Abstract (sommario):
Spring-born ram lambs were used to examine: (1) sexual maturational changes in LH, FSH and prolactin (PRL) secretion, testicular gonadotropin receptors, and testicular size and function; (2) predictability of yearling ram reproductive function from juvenile testicular size and reproductive hormone measurements. Despite continuous increases in testis size, serum LH-profile characteristics became greatest between 2 and 4 months and declined thereafter. However, LH-peak frequency increased by about 2-fold between 6 and 7 months; this was associated with marked increases in testosterone (T) secretion and spermatogenic function. Mean FSH and PRL levels were maximum at 2 months and 3 to 5 months, respectively, and decreased thereafter. Increases in steroidogenic and spermatogenic function were due partly to increases in testicular content of LH and FSH receptors. Yearling ram testis size and spermatogenic function were predictable from testis size at 5 to 6 months, neonatal (50 days) secretion of LH and T, and pubertal (150 days) secretion of T. However, combinations of testicular size and reproductive hormone measurements provided greater predictive power.
19
Chandrasekhar, Yallampalli. "Interactions between thyroid hormones and reproductive function in prepubertal and sexually mature merino rams /". Title page, contents and summary only, 1985. http://web4.library.adelaide.edu.au/theses/09PH/09phc4567.pdf.
20
Rosa, Henrique Jose Duarte. "The effect of the intensity of stimulation upon the response of seasonal anoestrous ewes to the introduction of rams". Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266740.
21
Vasquez, Hidalgo Manuel Alexander. "Effects of Nutrient Restriction, Realimentation, and Twinning on Plasma Volume, Umbilical Hemodynamics and Placental Characteristics in the Pregnant Adolescent Ewe". Diss., North Dakota State University, 2019. https://hdl.handle.net/10365/31573.
Abstract (sommario):
Reproductive physiology in production animals is a key economic component of longevity and profitability of animal farming. There are several components that can benefit or compromise adequate pregnancy periods. Sheep production is not only a very important economic activity for farmers around the United States, but sheep are also an important medical and surgical model to study human diseases. Our findings suggest that estradiol-17 beta could be involved in acute increased plasma volume early in gestation which can benefit overall gestation. We report that umbilical blood flow decreases upon nutrient restriction in adolescent ewes and does not recover upon realimentation. Finally, we suggest that a similar umbilical blood flow, placental development and plasma volume expansion in twins and singleton pregnancies could be enough to obtain similar birthweights in singletons and twins.
22
Quintana, Casares Pablo Ignacio. "Studies on the relationship between characteristics of ram semen and fertility". Title page, contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phq7.pdf.
Abstract (sommario):
Includes bibliographical references (leaves 274-316) Examines several aspects of male reproduction in the sheep, and how these are related to fertility in the female when semen is introduced by natural mating or artificial insemination.
23
Kiyma, Zekeriya. "Effects of feed restriction and dietary oil supplementation on reproduction in sheep". Laramie, Wyo. : University of Wyoming, 2005. http://proquest.umi.com/pqdweb?did=888862061&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
24
Dobbins, Adam Bradley. "Potential mechanisms linking nutrition and neuroendocrine control of reproduction in the sheep". Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3615.
Abstract (sommario):
Thesis (M.S.)--West Virginia University, 2004.Title from document title page. Document formatted into pages; contains iv, 124 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 82-124).
25
Al-Shorepy, Salih Abdu. "Selection to improve spring fertility in a crossbred sheep population". Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/40136.
Abstract (sommario):
Reproductive and productive performance of a composite sheep population, containing 50% Dorset, 25% Rambouillet and 25% Finn sheep breeding and under selection for ability to lamb in the fall, was evaluated. Traits considered were spring fertility, faIl litter size, live weights at birth, weaning, and at about 90 and 120 d of age, and scrotal circumference at weaning and at about 90 and 120 d of age. Fertility was defined as 1 or 0 depending upon whether a ewe lambed or failed to lamb, respectively, in fall. Litter size was defined as the number of lambs born per ewe lambing. A total of 1,102 exposures were used. Fertility averaged .59 for adult ewes (3 years and older), .45 for second-lambing ewes and .11 for yearling ewes (12 months old). Mean litter size averaged 1.89 across seasons and ages. Scrotal circumferences (SC) and body weights (WT) were measured at means of65, 96 and 128 d. Data were collected on 1878 lambs over 5 years; 63 sires and 420 dams were represented.
Genetic parameters were estimated by restricted maximum likelihood (REML) using various animal models. Heritability estimates for spring fertility ranged from .07 to .11. Litter size heritability was .05 for fall lambing and .10 for all lambings. Heritability estimates for weights from birth to 120 d ranged from .04 to . 19. Heritabilities for SC ranged from .02 to .25. Estimated genetic correlations among weights were large, and ranged from. 77 to unity. The genetic correlations of litter size with birth weight (BWT), 90-d weight (90WT) and 90-d scrotal circumference (90SC) were .17, .33 and .36, respectively. Genetic correlations of spring fertility with BWT, 90WT and 90SC were .22, -.31 and .29, respectively.
Mixed model methodology was applied to estimate genetic trends for fertility, litter size, BWT, weaning weight (WWT), 90WT and 90SC resulting from selection for fall lambing. Positive genetic gains in both spring fertility and fall litter size were observed. Rate of increase was higher for fertility than litter size, which was due to direct selection for fertility. Selection for spring fertility did not cause significant correlated changes in BWT, WWT, 90WT or 90SC. Thus, no genetic antagonisms resulted from the selection for fall lambing.Ph. D.
26
Falchi, Laura. "Transcervical artificial insemination and physiology of the cervix of the sheep". Thesis, Royal Veterinary College (University of London), 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558963.
27
Baker, Susan Jane. "Regulation of gonadotropin receptors in the testis of the adult ram". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72092.
Abstract (sommario):
Factors influencing testicular gonadotropin receptors and testis responsiveness to luteinizing hormone (LH) stimulation were studied during the seasonal sexual cycle of the adult ram. The normal variation in testis content of gonadotropin receptors was mapped out in relation to changes in (1) testis size, (2) testis responsiveness to LH stimulation and (3) mean serum concentration of LH, follicle stimulating hormone (FSH), testosterone and prolactin (PRL). The increase in gonadotropin receptor numbers during testicular redevelopment was preceded by elevated serum concentrations of PRL and associated with increases in both the frequency of endogenous pulses of LH and the responsiveness of the testis to LH stimulation. When serum PRL concentrations displayed abnormal variations in relation to photoperiod, the normal patterns of change in testis LH receptors and responsiveness to LH stimulation were altered. To determine if the increase in gonadotropin receptors was due to increased frequency of LH pulses up regulating homologous receptors, rams were injected, in the nonbreeding season with small, frequent doses of LH. Testis responsiveness was greatly enhanced but occurred independently of changes in gonadotropin receptor numbers or their binding affinities. To determine if the seasonal rise in serum PRL concentration was influencing gonadotropin receptors, endogenous secretion was suppressed by treatment with 2-bromo-X-ergocryptine (CB154) prior to and during testicular redevelopment. This resulted in delayed testicular redevelopment and reduced numbers of testicular LH receptors. Reduced numbers of LH receptors was associated with reduced responsiveness of the testis to LH stimulation. These results support the hypothesis that the seasonal increase in serum PRL concentration initiates testicular redevelopment by increasing LH receptors. Increases in LH peak frequency enhance responsiveness but this occurs independently of changes in gonadotropin receptors.
28
Kassem, Riad. "Reproduction in the Awassi ewe particular reference to increasing efficiency under semi-arid conditions". Thesis, Bangor University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328270.
29
Jordan, Katherine Mead. "Characterization of seasonal reproduction in Virginia Tech Selection Line, St. Croix, and Suffolk ewes". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28663.
Abstract (sommario):
This dissertation research contained three studies. The first two studies were conducted to investigate the ability of ewes to rebreed while lactating during seasonal anestrus. Breeds studied included the Virginia Tech Out-of-season (OOS) Line, which is a wool line genetically selected to lamb in the fall, and the St. Croix, a hair breed of tropical origin thought to be lowly seasonal. When January-lambing ewes were exposed to rams while lactating in April, significantly more OOS than St. Croix ewes were marked by rams in the first 21 d and total 39 d of ram exposure (58.3 vs. 8.7%, P = 0.0003 and 95.8 vs. 43.5%, P < 0.0001). Percentages of ewes diagnosed pregnant (53.2%) and percentages of ewes lambing (41.3%) were not different between breeds. When March-lambing OOS ewes were exposed to rams while lactating in May, 52.9% of ewes were marked though only 20% of ewes exposed to rams gave birth to viable lambs. Both OOS and St. Croix ewes appear to be well suited to accelerated production systems involving 7 to 8 mo lambing intervals. However, reduction of lambing intervals to 6 to 7 mo appeared to have detrimental effects on fetal survival in OOS ewes.
In a third study, alterations in endocrine profiles associated with differing degrees of hypothalamic sensitivity to estradiol-negative feedback and changing daylength in OOS, St. Croix, and Suffolk ewes in the absence of rams were investigated for 1 yr. The results show for the first time that based on progesterone profiles from intact ewes, St. Croix ewes do not have shorter anestrous periods than ewes of wool breeds, as previously thought. Based on luteinizing hormone profiles from ovariectomized ewes treated with estradiol implants, the duration of luteinizing hormone inhibition was shorter in OOS than Suffolk ewes (68 vs. 170.2 d, P = 0.02), but was not different from that found in St. Croix ewes (124.8 d). Specific roles for thyroxine and prolactin in timing the breeding season could not be assigned. This study was the first known use of the ovariectomized, estradiol-implanted ewe model to compare degree of reproductive seasonality in different breeds.Ph. D.
30
Nugent, Russell A. III. "Effects of breed and ram exposure on Spring estrous behavior and Summer fertility in domestic ewes". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/44057.
Abstract (sommario):
The present studies were conducted to check the effects
of acute ram introduction into a flock of anestrus ewes in
Virginia. Ewes were bled via jugular venipuncture twice
weekly and serum samples were radioimmunoassayed for
progesterone (P4) content as an indicator of estrous activity.
All rams were fitted with crayon equipped marking harnesses
for use as an indicator of mating behavior in ewes.
The first study tested the effects of introduction of
vasectomized rams into a flock: of' 50 Dorset (D) and 50
Hampshire (H) purebred ewes in either May or June. More D
ewes ovulated (96% vs 72% for H ewes) and mated (80% vs 20%
for H ewes) in May. Of ewes which mated in May 65% D but no
H ewes continued to cycle in June after removal of rams. Of
ewes exposed to rams in June no difference among breeds was
observed in percentage of ewes ovulating but more D ewes
(72%) mated than H ewes (44%). Twenty-four percent of D but
no H ewes cycled continuously throughout the 68 d or the
study. Lambing date significantly affected mating behavior
in H but not D ewes.
The second study tested the effects of ram breed on incidence
of mating and subsequent lambing in Rambouillet x
Q Suffollk ewes In June and July of 1984 and 1985. Ewes were
Q pre-exposed to either confined Suffolk (S) or Dorset (D)
Q yearling rams or no (N) ram for 2 wk prior to breeding by
Q either S or D rams. Lambing date was significantly affected
by breeding treatment in 1984 and by pre-exposure treatment
in 1985. Sixty-three percent of the ewes lambed in 1984
while 65% lambed in 1985.Master of Science
31
Long, Amanda Marie. "Impacts of Flax on Female and Male Reproductive Traits When Supplemented Prior to Breeding in Sheep". Thesis, North Dakota State University, 2018. https://hdl.handle.net/10365/29877.
Abstract (sommario):
Two experiments determined the effects of flaxseed supplementation on reproductive parameters in sheep. In experiment one, 240 multiparous Rambouillet ewes were assigned to one of two treatments: basal ration alone or basal ration with a Flaxlic® Sheep Tub offered over 35 days. Serum was collected weekly for progesterone (P4). Flaxseed supplementation did not improve progesterone concentration or reproductive parameters (P ≥ 0.26). In experiment two, 120 Rambouillet ram lambs were assigned to one of two treatments: basal ration alone or basal ration with a Flaxlic® Sheep Tub offered over 112 days. Scrotal circumference measurements, serum for testosterone, and semen were collected on day 84 and 112. Day effects were found for select semen measurements, testosterone, weight, and scrotal circumference (P ≤ 0.05). There was no effect of treatment on testosterone concentration (P = 0.99) or any semen quality characteristics (P ≥ 0.33). Overall, tub supplementation did not alter reproductive ability.
32
Robinson, Julie A. "The effects of dietary molybdenum and sulfur on serum copper concentrations, growth and reproductive function in lambs". Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/31319.
Abstract (sommario):
Feeds often contain molybdenum (Mo) and sulfur (S) in excess of recommended allowances for adequate copper (Cu) absorption by ruminant livestock. Two randomized-block experiments were conducted using lambs given a cereal-based diet (90% of dry matter (DM) intake), containing 8 mg Cu, 0.7 mg Mo and 2.1g S per kg DM, that was either unsupplemented or supplemented with ammonium molybdate or sodium sulfate alone or in combination, to determine the effects of Mo, S and Mo+S on growth, hematology, serum Cu and Mo concentrations and reproductive function.
Short term intake (4 weeks) by rams, aged 18 and 20 weeks, of 26 mg Mo alone or in combination with 2g S per kg DM, had no effect on growth, hematology or the concentration of total Cu in serum (TCu). However, supplemented groups had lower (P<0.05) concentrations of serum Cu soluble in trichloroacetic acid (TCA-Cu), but the group given Mo+S had the highest (P<0.05) concentration of serum residual Cu (RCu). Luteinizing hormone (LH) peak amplitude was affected by age*diet interaction (P<0.05), because of high amplitude LH peaks in the serum of lambs, aged 24 wks, given Mo alone. Testosterone serum secretory profiles did not differ among diet groups, but testosterone peak frequency was higher (P<0.05) for older ram lambs.
Long term intake (32-39 wks) by ewe, ram and wether lambs (gonadal influence) of 12 mg Mo, or 2g S alone or combined per kg DM also had no effect on hematology or TCu. Food intake and liver weights were higher (P<0.05), but TCA-Cu was lower (P<0.05) for groups given S. Serum concentrations of total Mo (TMo) were higher (P<0.05) for Mo-supplemented groups, but RCu was highest only for the Mo+S group. Growth was affected by Mo*S*gonadal influence*time interaction (P<0.05); until autumn, the body weight of Mo-supplemented groups were higher than those of ram and wether lambs given Mo+S. Ovarian or testicular functions were delayed more severely for Mo- than Mo+S-supplemented groups. Mean concentrations of LH were affected by Mo*S*gonadal influence*time interaction (P<0.05); the mean LH values of Mo-supplemented ram and ewe lambs were higher than the Mo+S-supplemented
group, whereas a reverse trend was observed for wether lambs. The amplitude of LH peaks was affected by Mo*S*gonadal influence*time interaction (P<0.05); for ram lambs, LH peak amplitude was higher for Mo than Mo+S-supplemented groups, whereas for wether and ewe lambs the reverse trend was noted. Mean concentrations of serum Cortisol and Cortisol peak amplitude were affected by Mo*S interaction (P<0.05); the mean Cortisol concentration and peak amplitude for the Mo-supplemented group were higher than those for the Mo+S-supplemented group. The frequency of LH and Cortisol peaks did not differ (P>0.10) among diet groups.
In conclusion, Mo supplementation of cereal-based diets containing a high concentration of Cu did not adversely affect lamb growth. However, the effect of high dietary Mo on reproductive function appears to depend on the dietary level of S and the induction of high serum RCu (thiomolybdate). Further investigations on the effects of Mo and thiomolybdate on endocrine function may provide a nutritional basis for improving reproductive efficiency in ruminants.Land and Food Systems, Faculty of
Graduate
33
Ribeiro, Mafalda Maria dos Santos Vidal. "Caracterização produtiva e reprodutiva do rebanho de raça Merino Branco da Fundação Eugénio D'Almeida". Master's thesis, ISA/UTL, 2012. http://hdl.handle.net/10400.5/5296.
34
Hartman, Carina. "A mixed-model evaluation for growth and reproduction parameters in a SA mutton Merino flock". Diss., Pretoria : [s.n.], 2000. http://upetd.up.ac.za/thesis/available/etd-01242003-092447.
35
Schoombee, Cornelius Johan Albertus. "The Damara sheep : an appraisal of its reproductive performance and potential". Thesis, Stellenbosch : University of Stellenbosch, 1998. http://hdl.handle.net/10019.1/5481.
36
Skinner, Donal C. "The pars tuberalis and its possible role in the control of seasonal reproduction in sheep". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320052.
37
Rao, Shaoqi. "Genetic Analysis of Sheep Discrete Reproductive Traits Using Simulation and Field Data". Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30490.
Abstract (sommario):
The applicability of restricted maximum likelihood (REML) in genetic analyses of categorical data was evaluated using simulation and field data. Four genetic models were used to simulate underlying phenotypic variates, which were derived as the sum of additive genetic and environmental effects (Model 1A and 1B) or additive genetic and permanent and temporary environmental effects (Model 2A and 2B). Fifty-eight replicates were simulated, each of which contained 5000 ewes by 500 sires and 5000 dams and with up to five records per ewe. The usual transformation of heritability estimated on the categorical scale to the normal scale for fertility and litter size performed better for a simple animal model than for a repeatability model. Genetic correlation estimates between the two categorical traits for Model 1B and 2B were .49 ± .01 and .48 ± .04, respectively, and were close to the expected value of .50. However, permanent and temporary environmental correlations whose input values were each .50 were underestimated with estimates of .41 ± .05 and .26 ± .03, respectively for Model 2B, and .33 ± .02 for the temporary environmental correlation for Model 1B.
Bivariate genetic analyses of litter size with growth and fleece traits were carried out by REML for the data of Suffolk, Targhee and Polypay. Direct heritabilities for most growth traits in all the breeds were low (<.20). Maternal genetic and maternal permanent environmental effects were important for all body weights except for the weaning weight at 120 d for Polypay sheep. Estimates of heritability and permanent environmental effects for litter size for these breeds ranged from .09 to .12 and .00 to .05, respectively. Heritabilities for grease fleece weight and fiber diameter were high for Targhee and Polypay sheep. Direct genetic correlations between growth and litter size were favorable for Suffolk and Targhee but weak for Polypay sheep. Genetic correlations between maternal effects for growth and direct effects for litter size for the breeds were generally small. Within-trait maternal-direct genetic correlations for growth in the breeds were variable and generally negative. Direct genetic correlations of litter size with grease fleece weight and fiber diameter were variable across the breeds.Ph. D.
38
Lier, Elize van. "Sex differences in response to adrenocorticotropin (ACTH) administration in sheep /". Uppsala : Dept. of Clinical Chemistry, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/v157.pdf.
39
Vanimisetti, Hima Bindu. "Genetic evaluation of ewe productivity and its component traits in Katahdin and Polypay sheep". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29760.
Abstract (sommario):
The objectives of this dissertation were to evaluate genetic influences on ewe productivity, its growth and reproductive components, and measures indicative of accelerated lambing performance. Genetic parameters were estimated for total weight of litter weaned per ewe lambing (TW) and its components, number of lambs born (NB), number of lambs weaned (NW) and average weight of lambs weaned (AW), measured as traits of the ewe, and lamb survival (LS) and weaning weight (WW), measured as traits of the lamb, in Katahdin sheep. Heritabilities of TW, NB, NW, and AW, were 0.12, 0.12, 0.09, and 0.13, respectively. Heritability of WW was 0.15 to 0.20. Genetic effects on LS were negligible. Genetic correlation of TW with NB, NW, and AW averaged 0.30, 0.90, and 0.74, respectively, those of NB with NW and AW averaged 0.72 and 0.01, respectively, and that between NW and AW averaged 0.50. Direct genetic effects on WW were independent of NB and NW, but correlation between maternal genetic effects on WW and animal genetic effects on NW averaged 0.35.
Ewe fertility, NB, LS, and WW were modeled using stochastic simulation and used to derive NW, AW, and TW to test alternative predictors of genetic merit for TW. A random 8% of WW observations were set to missing values and AW and TW were recalculated to evaluate the effects of data reporting inconsistencies on efficacy of different prediction strategies. Four alternative predictors of estimated breeding values (EBV) for TW involved direct univariate prediction (TW1), an index of EBV for NW and AW (TW2), indirect prediction using data for NW and AW and genetic correlations among NW, AW and TW (TW3), and indirect prediction augmenting TW3 with data and genetic correlations involving NB (TW4). To validate efficacy of predictors, daughter data sets were generated from the original ewes and their realized TW were regressed on alternative predictors. Regression coefficients from TW1, TW3, and TW4 were close to the expected value of 0.50 whereas those from TW2 were less than 0.50. Model Rsquare statistics were similar among predictors when there were no missing WW data but regressions involving TW1 had lowest model R-square when some WW data was missing.
Ewe lamb fertility (ELF), ages at first, second, and third lambings (AGE1 to AGE3), first and second lambing intervals (INT1 and INT2), and number of lambings by 38 mo of age (LAMB3) were evaluated for an accelerated lambing Polypay flock. Relationships among these traits and NB and WW were estimated. Heritability of ELF, AGE1, AGE2, AGE3, INT1, INT2, and LAMB3 were 0.14, 0.39, 0.28, 0.36, 0.00, 0.09, and 0.27, respectively. Heritability of AGE2 and AGE3 were negligible after accounting for variation in AGE1. Genetic correlations of ELF with AGE1 and AGE2 were -0.89, -0.91, respectively, and that with LAMB3 was 0.89. Genetic correlations of LAMB3 with AGE1 and AGE2 were -0.49 and -1.00, respectively. Genetic correlations of ELF and LAMB3 with direct genetic effects on WW were close to -0.70, but correlations with maternal genetic effects on WW were 0.88 and 0.58, respectively. Prolificacy was independent of ELF and LAMB3.Ph. D.
40
Fossceco, Stewart Lee. "Logistic growth curve parameter estimates for scrotal circumference and relationships with female reproduction in crossbred sheep". Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/37241.
Abstract (sommario):
Data from two groups of lambs were analyzed. In group one, seasonal patterns of testis growth through 16 mo of age were assessed on 40 spring-born ram lambs (eight Barbados Blackbelly, 10 Suffolk and 22 1/2-Dorset, 1/4-Finnish Landrace, 1/4-Rambouillet). Scrotal circumference (sc) and body weight (wt) were measured at mean ages of 30, 62, 96, 124, 153, 180, 212, 243, 290, 333, 364, 398, 427, 454, 488 and 517 d. A multivariate repeated measures analysis indicated that there were breed differences in ram sc and wt measurements at each age. When logistic growth curves were fit to ram sc data, breed differences were associated with parameters of the logistic curve that defined mature testis size and the period of rapid testis growth.
For group two, data were collected on 1,044 lambs from 727 spring lambings over 5 years; 67 sires and 525 dams were represented. Sc and wt were measured in rams at 5 times (mean ages of 44, 63, 97, 129 and 156 d); ewes were weighed at these times and at three additional times (187, 230 and 271 d). All ewe lambs were kept for fall breeding. Fertility, prolificacy and postweaning spring mating behavior of ewes that had lambed were measured. After ewes lambed, they were exposed to vasectomized rams and checked for postweaning spring mating behavior.
Restricted maximum likelihood (REML) was used to estimate variance components for additive genetic, ewe, and litter effects in group two Jambs. Heritability estimates for wt at birth to 150 d ranged from .14 to .42. Heritabilities for sc and sc scaled to the 1/3 power of body weight (rsc) ranged from .09 to .57 and from .13 to .55, respectively, and were largest at approximately 90 d. Logistic sc growth curves were fitted to data from individual ram lambs. Heritabilities of the estimated logistic parameters mature sc (A), sc maturing rate (k), age at inflection of the sc growth curve (t₁) and initial 14-d sc (SC14), were estimated at .09±.15, .17±.18, .37±.29 and .40±.14, respectively. Heritability estimates for fertility and spring mating behavior (spbrd) were .04±.13 and .41±.19, respectively. The heritability estimate for prolificacy was zero.
Longitudinal additive genetic covariances among wt, sc and rsc at the second, third and fourth measurements were estimated from approximate multivariate REML analysis treating variances as known. Estimated genetic correlations among wts were largest, and ranged from. 77 to .93. Estimated genetic correlations for rsc traits were between .48 and .90. Estimated genetic correlations for sc ranged only from .10 to .67. Pairwise genetic correlations among sc or rsc with fertility or spbrd were estimated to be moderate and positive (.20 and .34, respectively); t₁ had correlations of -.32 and -.48 with fertility and spbrd, respectively.Ph. D.
41
Helliwell, Rachel J. A. "Target sites for melatonin in the sheep with particular reference to the photoperiodic control of reproduction". Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602270.
Abstract (sommario):
The aim of this study was to identify the potential target sites for the action of melatonin in sheep and to relate the findings to the photoperiodic control of reproductive activity in the female. It has been proposed that melatonin may have a direct luteotrophic role in several species, therefore the first experiment in this thesis was designed to investigate if melatonin acts directly on the ovine ovary to enhance progesterone production. The oral administration of 3mg melatonin, daily at 1500h, to anoestrous Blackface ewes advanced the onset of oestrous cyclicity and was associated with an increase in ovulation rate, at the first overt oestrous, compared to naturally ovulating control ewes. Peripheral prolactin concentrations were significantly suppressed within 7 days of the start of melatonin treatment. The concentration of progesterone was determined in samples collected directly from the utero-ovarian vein, and compared to the pulsatile pattern of luteinizing hormone (LH) secretion determined from samples collected from the jugular vein. The pattern of progesterone secretion in the utero-ovarian vein was episodic. The majority of progesterone pulses occurred independently of the pulsatile pattern of LH secretion, although each pulse of LH was followed by an increase in progesterone concentration. During the luteal phase of the first overt oestrous cycle, the pulsatile pattern of LH secretion and the progesterone concentrations in the utero-ovarian venous plasma were similar for both melatonin-treated and naturally ovulating control ewes. This suggests that melatonin does not have a direct luteotrophic action on the ovine ovary. The experiment described in Chapter 6 was designed to investigate if the ovine foetus is sensitive to photoperiodic information while in utero and also to assess the effect of prenatal photoperiod experience on the endocrine status and timing of puberty of ewe lambs. Three groups of female lambs were studied. Groups A and B were raised on a common postnatal photoperiod consisting of a 10 week block of long days (18L:6D) from birth followed by short days (6L:18D) until the end of the experiment at 38 weeks of age. These two groups of lambs differed only in the photoperiod experienced by their mothers during gestation; those in Group A were exposed to short days and those in Group B were exposed to long days from day 25 of gestation to parturition. Lambs in Group C experienced long days prenatally and short days from birth until the end of the experiment. Peripheral prolactin concentrations of lambs on the day of birth were dependent on the photoperiod to which their mothers were exposed during gestation. For the first 10 weeks after birth plasma prolactin profiles of the lambs raised under long days (Groups A and B) were influenced by their prenatal photoperiodic experience. The number of female lambs which exhibited puberty following a decrease in day length from 18L:6D to 6D:18L at 10 weeks of age was increased by maintaining their mothers on long days as opposed to short days during gestation. Puberty was delayed in the majority of female lambs which were exposed to long days in utero followed by short days from birth (Group C). The results suggest that lambs are sensitive to photoperiodic information prior to birth and that female lambs must be exposed to a minimum number of long days prior to a decrease in daylength to time the onset of puberty.
42
Wagner, Hans-Gerhard R. "The impact of strategic anthelmintic treatments on reproduction and productivity in Djallonké sheep in the Gambia /". [S.l.] : [s.n.], 1995. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
43
Kakar, Muhammad Azam. "Effect of peri-conceptional feed intake on early embryo development and fetal growth in the Merino ewe /". Title page, table of contents and abstract only, 2003. http://web4.library.adelaide.edu.au/theses/09ANP/09anpk138.pdf.
44
Carpenter, Karen Denise. "The roles of estradiol-17 beta and prolactin in uterine gland development in the neonatal ewe". Texas A&M University, 2005. http://hdl.handle.net/1969.1/2731.
Abstract (sommario):
Endometrial glands are required for adult uterine function and develop post-natally
in mammalian species. Therefore, studies were conducted using neonatal ewes as a
model to determine: 1) the roles of estradiol-17-alpha and estrogen receptor-alpha (ER-beta) in
endometrial gland development; 2) the role of ovaries in endometrial gland
development; 3) the role of prolactin in endometrial gland development; and 4) factors
regulating prolactin receptor expression in endometrial glands.
Study one determined the effects of neonatal exposure of ewes to estradiol-17-alpha
valerate (EV); EM-800, an ER-beta antagonist; or CGS-20267, an aromatase inhibitor on
endometrial gland development. Results indicate E2-17-alpha does not regulate endometrial
gland differentiation or development. Additionally, ER-beta does not regulate primary
differentiation of glandular epithelium, but does influence coiling and branching
morphogenesis of endometrial glands.
Study two determined the effects of ovariectomy on endometrial gland
morphogenesis. Results suggest that the ovary and, thus, an ovarian-derived factor(s)
regulate, in part, the coiling and branching of endometrial glands. Expression of
subunits of activin, follistatin, and inhibin in the neonatal ovine ovary in addition to modulation of the components of the activin/follistatin system in the uterus of
ovariectomized ewes supports the hypothesis that the ovarian factors that influence
endometrial adenogenesis in the neonatal ewe may be activin, follistatin, and/or inhibin.
Studies three and four determined the role of prolactin in endometrial
adenogenesis in the neonatal ewe. Studies in which either hypoprolactinemia or
hyperprolactinemia were induced indicate that prolactin regulates ovine endometrial
adenogenesis in the neonatal ewe. The aim of study five was to determine transcription
factors that regulate the glandular epithelium specific expression of prolactin receptor.
Prolactin receptor exon 2 was cloned and sequenced, but no identifiable exon 1 or
promoter was found. Additionally, many bovine contigs containing portions of the
prolactin receptor gene were identified suggesting the bovine genome will be a useful
tool as it becomes more complete.
These results indicate ER-beta, prolactin and prolactin receptor, along with an
unidentified ovarian factor(s), influence endometrial gland development in the neonatal
ewe; however, exposure of the neonatal ewe to exogenous estradiol-17-alpha prevents
differentiation and development of endometrial glands.
45
Ilse, Breanne Rose. "Effects of Linseed Meal on Growth and Reproductive Performance in Ruminants". Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/28744.
Abstract (sommario):
Linseed meal (LSM) was fed to ovariectomized ewes exposed to estradiol 17-? (E2)
implants over time, and LSM was supplemented to beef cows during late gestation and
early lactation to evaluate the estrogenic potential of the phytoestrogen secoisolariciresinol
diglycoside (SDG) found in LSM. Forty-eight ovariectomized ewes were fed a diet
containing 12.5% LSM for 0, 1, 7, or 14 d and implanted with estradiol-17? (E2) for 0, 6,
or 24 h before tissue collection. Uterine cellular proliferation, vascularity, and the
expression of the angiogenic factors and their receptors were recorded. There was an
interaction of LSM and E2 on uterine mass (P = 0.05). At 24 h of E2 exposure,
proliferation was reduced (P < 0.001) when ewes were fed for 14 d compared to being fed
0 or 1 days. There was a LSM x E2 interaction (P ? 0.03) on VEGF receptor-2 (KDR) and
hasicfihrohlast growth factor receptor (FGFR2) decreasing by 24 h E2 exposure.
Exposure of LSM and E2 may impact the estrogenic response of sensitive tissue.
Two studies were conducted to examine the effects of supplementing beef cows
with LSM during late gestation or early lactation on calf growth and development. In
Experiment 1, multiparous cows received either LSM or a control (CON) supplement
(approximately 10% diet dry matter) for the last 60 d of gestation. Offspring weights,
ADG, heifer age at puberty, conception percentage and steer carcass characteristics were
recorded. In Experiment 2, multiparous cows received LSM or CON supplements
(approximately 10% diet dry matter) during the first 60 d of lactation, and only heifer calf
development performance was observed and recorded. Heifer calf weight, average daily
gain, and attainment of puberty were assessed. For both experiments, birth weight, weaning
weight and ADG were not affected (P > 0.31) by LSM supplementation. While final body
weights were heavier (P = 0.04) for steer calves in Experiment 1, there was no effect (P =
0.09) of supplementation on carcass characteristics. In Experiment 1 and 2, attainment of
puberty in heifer calves was not influenced (P > 0.58) by supplement type. Linseed meal
supplementation during late gestation or early lactation does not appear to have a negative
impact on calf growth, onset of puberty in heifer calves, or steer carcass quality,
implicating that it may make a good supplement choice in cattle.
46
Earl, Colin R. "The regulation of the timing of melatonin secretion in the sheep". Title page, summary and table of contents only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09phe12.pdf.
Abstract (sommario):
Includes bibliographical references (leaves 166-195) Addresses the nature of the central mechanisms involved in the regulation of the circadian pattern of secretion of the pineal hormone melatonin in the highly seasonal Suffolk breed of sheep. Provides new information on the behaviour of the onset and offset of melatonin secretion under different photoperiodic conditions.
47
Alhamada, Alhamada Moutaz. "Les chevauchements, enregistrés automatiquement lors de la reproduction des ovins, sont indicateurs de la libido des béliers et de la valeur reproductive des brebis". Thesis, Montpellier, SupAgro, 2016. http://www.theses.fr/2016NSAM0032/document.
Abstract (sommario):
La demande en produits animaux pousse les éleveurs à réduire les intrants et supprimer les traitements hormonaux pour la maîtrise de la reproduction des ovins. Ces exigences ont relancé les études sur des méthodes qui s’appuient davantage sur les comportements spontanés des mâles et des femelles. Le détecteur électronique des chaleurs, développé par l’UMR Selmet, semblait prometteur et il fallait l’accompagner de validations expérimentales. Ces études ont été réalisées en race Mérinos d’Arles du Domaine du Merle qui sont élevées en système d’élevage extensif et se reproduisent à contre saison. Nous avons tout d’abord validé ce détecteur sur des brebis suivies par vidéo. Nous montrons que 93% des chevauchements sont effectivement enregistrés et comme les brebis en œstrus acceptent plusieurs chevauchements : toutes les brebis sont détectées. Dans une deuxième étape nous avons utilisés plusieurs béliers avec des effectifs plus importants (n=60). Ceci nous a confirmé, pour la brebis des fortes variabilités 1) de la réponse aux traitements hormonaux, 2) de la durée des chaleurs et 3) du nombre de chevauchements par brebis. Pour les béliers, nous avons mis en évidence une forte dispersion du nombre de chevauchements qui s’est répétée, avec les mêmes brebis, sur les cycles suivants. Nous avons ensuite étudié plus précisément le comportement sexuel des béliers en les plaçant en test visuel (méthode de référence) avec quelques brebis en chaleur. Pour cela nous avons évalué 6 béliers entiers Mérinos et 6 béliers vasectomisés Mourérous, à un an d’intervalle lors de la lutte de printemps et aussi à celle d’automne. Nous avons retrouvé les amplitudes classiques des variations saisonnières sur les activités des béliers aux trois saisons.Nous avons montré que la libido des mâles définie par la somme de leurs activités pré-copulatoires ou copulatoires était bien corrélée (r=+0,80, n=18) aux chevauchements mesurés avec le détecteur sur plusieurs centaines de brebis la libido peut être assimilée aux activités copulatoires que nous mesurons avec les chevauchements. De plus, nous obtenons une corrélation claire entre les activités copulatoires observées et collectées automatiquement en troupeaux. Le classement des béliers selon leur libido sont était très répétable intra-saison (de cycle a l’autre) et enter-saison (d’une saison à l’autre). A un an d’intervalle la répétabilité a été meilleur (94%) avec les chevauchements qu’avec les mesures des tests (80%). Sachant que la fertilité des brebis sous-alimentées est plus faible, nous avons étudié les comportements de brebis ayant subi 3 régimes alimentaires contrastés appliqués pendant 3 mois. Nous montrons que la réceptivité et la proceptivité de brebis ne changent pas selon leur état nutritionnel, par contre leur capacité à attirer les béliers (attractivité) est d’autant plus forte qu’elles sont plus lourdes et/ou qu’elles avaient des profils métaboliques favorables (métabolites et hormones). Ces données, obtenues en lot expérimental par des méthodes de référence, ont été validées en troupeau avec le détecteur électronique. Dans la discussion générale, nous reprenons nos résultats pour montrer qu’en système d’élevage extensif les brebis jouent un rôle central dans l’attraction, ou pas, des béliers. Ces béliers, bien que choisis pour la reproduction, ont des libidos très variables mais répétables. Le détecteur de chaleur, inclus dans un système d’élevage de précision, pourrait servir en élevage pour améliorer la reproduction des ovins en s’appuyant sur ces connaissancesAutomatically recorded mountings of rams provide information on their libido and breeding value of ewes.Abstract:The demand for livestock products pushes farmers to reduce inputs and remove hormonal treatments used to control ewe’s reproduction. These trends put forward research lines that are aimed to study sexual behaviours of both rams and ewes. The electronic oestrus detector, developed by UMR Selmet, looked promising but still had to be accompanied by further experimental validation. Our studies were conducted on Merino’s d’Arles sheep of Domaine de Merle, which are bred in an extensive farming system with a mating period occurring in spring as many other Mediterranean breeds. Our first step was to validate the electronic detector on sheep by comparison to video observation. We showed that 93% of mounts are registered, and as ewes in oestrus accept multiple mounts: all the ewes are detected with this device. In a second step we used several rams (n=6) with a larger number of ewes (n = 60). This confirmed that ewes express a strong variability 1) of the timed response to hormonal treatments, 2) of the oestrus duration and 3) the total number of mounts per ewe. We also demonstrated that the wide dispersion of the number of mounts done by rams was however repeated, with the same flock, in subsequent cycles.Then, we focussed on ram sexual behaviour by placing them with few oestrus ewes under visual test (the reference method). We evaluated 6 intact Merino rams and 6 vasectomized rams of the Mourerous breed, this test was done thrice: at spring one year apart and also at the autumn. We found conventional amplitude of seasonal variations on the activities of rams during the three seasons. We demonstrated that male libido, defined by the sum of their pre-copulatory and copulatory activity, was well correlated (r = + 0.80, n = 18) with the counted mounts by the detector of the same rams but with several hundreds of ewes. Therefore, the libido can be estimated by number of mounts. In addition, we get a clear correlation between the observed copulatory activities and automatically collected mounts within a flock of ewes. We found that ranked rams’ libido scores are repeated. This is very stable within-season (one cycle) and between-seasons (from one season to the next). A one year apart repeatability of mounts was better (94%) within the flock than when measured by mounts number during tests (80%). Given that fertility of undernourished ewes is lower, we studied the behavior of ewes that underwent three contrasting diets applied for 3 months. We observed that receptivity and proceptivity of ewes do not change according to their nutritional status, through against their ability to attract the rams (attractiveness) is much stronger if they are heavier and/or had favorable metabolic profiles (metabolites and hormones). These results were further confirmed within rams’ mating flock (when bodyweight are widespread). In the discussion, we resume our results that show that within extensive livestock system, ewe plays a central role in attracting or not the rams. These rams, although chosen for breeding, have very variable but repeated libido score. The electronic oestrus detector, included in a precision farming system, could be used to improve the breeding of sheep, based on this knowledge.Keywords: sexual behaviour, preferential mating, libido, attractiveness, receptiveness, proceptivity and precision farming
48
Hanon, Elodie. "A novel model of action for TSH (thyrotropin stimulating hormone) in the mammalian neuroendocrine system". Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=53386.
49
Stradiotto, Monalissa de Melo [UNESP]. "Efeito da gordura protegida sobre a composição do leite, anestro pós-parto, resposta às infecções parasitárias e desempenho de cordeiros, em ovelhas da raça Bergamácia". Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/96628.
Abstract (sommario):
Made available in DSpace on 2014-06-11T19:28:24Z (GMT). No. of bitstreams: 0
Previous issue date: 2007-07-31Bitstream added on 2014-06-13T20:58:04Z : No. of bitstreams: 1
stradiotto_mm_me_botfmvz.pdf: 530763 bytes, checksum: e4530e5d16068efeff8131c5fdeac6fc (MD5)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Universidade Estadual Paulista (UNESP)
No Brasil, muito pouco se conhece sobre o leite ovino, pois a maioria das raças brasileiras são especializadas para a produção de carne ou lã, mas é possível encontrar animais com aptidão leiteira. O presente trabalho teve o objetivo de avaliar o efeito da gordura protegida na composição do leite, duração do anestro pós-parto, resposta às infecções parasitárias e desempenho dos cordeiros, em ovelhas da raça Bergamácia. Utilizou-se 77 ovelhas distribuídas em 2 grupos por ordem de parição e idade, em dois tratamentos: dieta Controle (C): silagem de milho e concentrado; e dieta com Gordura Protegida (GP): a mesma de C e adição de gordura ruminalmente protegida (35 g/ovelha/dia) ao concentrado. As dietas foram isoenergéticas e isoprotéicas, contendo 70% NDT e 16% PB com base na matéria seca. Os cordeiros permaneceram com suas mães até 45 dias de idade, quando foram desmamados. As ovelhas, 48 horas pós-parto, foram ordenhadas mecanicamente uma vez ao dia, às 7h 00, com produção de leite mensurada diariamente pelo período de 60 dias. Amostras de leite foram coletadas semanalmente para análise da composição centesimal e teor de caseína. O tratamento GP apresentou maior produção de leite média diária após a desmama (0,531 vs 0,489 kg/cab/dia), entretanto, a produção de todo o período experimental não foi diferente entre os tratamentos (0,453 vs 0,468 kg/cab/dia, para C e GP, respectivamente). Não foram observadas diferenças entre tratamentos para os teores de gordura do leite até a 6ª semana de lactação, sendo verificadas apenas após a desmama. Ambos teores de alfa e beta caseínas apresentaram diferenças entre tratamentos (30,00 vs 18,50 Kda para alfa caseína e 32,48 vs 25,65 Kda para beta caseína, para os tratamentos C e GP respectivamente). O sistema de produção utilizado provavelmente foi uma variável importante nos resultados...
Little is known about sheep milk in Brazil because the majority of Brazilian breeds are for meat production or wool, but is possible to find some type milk animals. The present work aimed to evaluated the effect of protected fat on milk composition, time to estrus regress after lambing, gastrointestinal nematodes infections and lamb performance of Bergamasca ewes. It were used 77 ewes allocated in 2 homogenous groups by parity and age. Diet control (C): corn silage and concentrate; diet with protected fat (GP): same of C and protected fat added (35 g/ewe/day) to the concentrate. Diets were isoenergetic and isonitrogenous with 16% of CP and 70% of TDN on dry matter basis. In both groups, lambs were kept with their mothers in pasture during the day, being separated at night. After morning milking, lambs were returned to their mothers, being weaned at 45 days of age. Ewes from both groups were mechanically milked for 60 days. Treatment GP presented higher daily average milk productionafter lambs weaning (0.5351 vs 0.489 kg/head/d), horewer, average milk production of the whole period was not different (0.453 vs 0.468 kg/head/d for C and GP, respectively). There was no found difference between treatments for fat content milk until 6th week of lactation. Alfa e beta casein content has presented differences between treatment (30,00 vs 18,50 Kda for alfa casein and 32,48 vs 25,65 Kda for beta casein, for C e GP respectively). The production system used probably was an important variable in that results due to lamb presence during a moment in the day induced milk retention during ewe machine milking.
50
Griffith, Ronald D. "Thyroid hormones are required during long-day photoperiods for the establishment of estradiol-sensitive afferent input to and activation of, dopaminergic neurons in the A15 area of the ovine hypothalamus". Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1580.
Abstract (sommario):
Thesis (M.S.)--West Virginia University, 2000.Title from document title page. Document formatted into pages; contains viii, 46 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 33-38).