Rozprawy doktorskie na temat „Beef cows”

Thesis (M.S.)--University of Nevada, Reno, 2008.
"December, 2008." Includes bibliographical references (leaves 27-31). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2009]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.

Doctor of Philosophy
Department of Animal Sciences and Industry
Jeffrey S. Stevenson
Four experiments were conducted in beef cows to determine factors that increased the probability of pregnancy per AI when cows are inseminated by appointment. Cows in all experiments were inseminated after a 7-d CO-Synch + CIDR program (100 μg GnRH [2 mL Factrel, Pfizer Animal Health, Whitehouse Station, NJ] 7 d before 25 mg PGF₂[subscript]α [d 0; 5 mL Lutalyse; Pfizer Animal Health]). Experiment 1 compared 1 vs. 2 inseminations and GnRH injection times at 60 and 75 h after the CO-Synch + CIDR program. Delaying AI until 75 h, according to interpretation of estrus-detection patches, for cows not in estrus by 60 h after CIDR insert removal increased (P < 0.05) pregnancy risk (PR) compared with cows not in estrus and inseminated at 60 h (51.4 vs. 41.7%), respectively. The necessity of GnRH injection concurrent with AI was tested in experiment 2. Cows displaying estrus by 65 h that were injected with GnRH had similar PR to cows in estrus and not treated with GnRH (61.9 vs. 60.4%), respectively. Cows in experiment 2 that did not display estrus, but were treated with a GnRH injection at 65 h and then inseminated at 84 h after CIDR insert removal had increased PR compared with similar cows not treated with GnRH (33.4 vs. 15.0%; P < 0.01), respectively. Experiments 3 and 4 were observational studies conducted to determine if blood metabolites glucose and beta-hydroxy butyrate (BHB experiment 3), or physical body and blood metabolites, (glucose, BHB, non-esterified fatty acids [NEFA], blood urea nitrogen [BUN], body weight, rump fat [RF], or BCS; experiment 4) were indicative of future reproductive success in suckled beef cows enrolled in a timed AI program. In experiment 3, plasma glucose concentration 10 d before AI was lesser (P = 0.01; 52.2 vs. 56.9 mg/dL) and serum BHB concentration was lesser (P < 0.01) in cows that became pregnant 35 d after timed AI than for cows that did not become pregnant (600 vs. 690 μM), respectively. Experiment 4 identified relationships between indicators and reproductive success including the finding that serum NEFA concentration 2 to 4 wk before AI is negatively correlated (P < 0.05) with PR to AI.

An estrus synchronization trial was conducted to determine the efficacy of adding an injection of gonadotropin releasing hormone (GnRH) at initiation of the controlled intravaginal drug releasing device (CIDR®) progesterone synchronization protocol in heifers. Nulliparous (n=121) beef heifers were randomly assigned to one of two treatment groups. All heifers received a CIDR® implant at the initiation of the breeding season. Half of the heifers (Select Synch) received an injection of GnRH. Heifers in the Select Synch treatment group had a lower numerical response (76.7% versus 88.3%) to treatment (detected in heat) and an overall lower artificial conception rate (46.0% versus 53.3%), but no statistical difference was detected. Days to conception and artificial insemination conception rates for both groups were similar for all heifers inseminated. Three hundred multiparous Hereford, crossbred and composite beef cows were assigned to one of two breeding groups (Early and Late) based on calving date and randomly assigned to receive an injection of GnRH at the time of CIDR® insertion (Select Synch). The addition of GnRH did not impact the percentage of cows detected in estrus or days to conception. Conception rates were not affected by the addition of GnRH (Select Synch), however cows in the early breeding group were more likely to become pregnant (58% versus 45%) by artificial insemination (P<0.02). An experiment evaluated the efficacy of the CIDR® protocol to synchronize estrus in Arizona Holstein dairy cows (n=696). Cows assigned to the CIDR® protocol (n=337) received a CIDR® insert at the end of the voluntary waiting period (55 days). CIDR®s were removed and an injection of prostaglandin was administered seven days after insertion. There was no difference due to CIDR® treatment in number of services per conception or first service conception rate. CIDR® treatment reduced days to first service, days open at first service, and days open (P<0.02). Warm season had a deleterious effect on number of services, days to first service, first service conception rate and days open (P<0.0001). In summary, estrus synchronization improved postpartum reproductive performance; however, thermal stress continues to be a major barrier to reproductive efficiency.

Improved prediction of forage quality and cow performance may enhance the nutritional management of beef cows. In two 12 mo trials, mature beef cows (n=136) grazing tall fescue pastures were used to compare estimates of forage quality and animal performance. Forage quality was estimated by proximate analysis of forage samples (FOR) or by near infrared reflectance spectroscopy of fecal samples (FNIR). Nutritional Balance Analyzer (NutBal), NutBalPro and 1996 NRC Nutrient Requirements of Beef Cattle (NRC) programs were used to predict animal performance. The objectives were to compare FOR and FNIR estimates of CP and TDN and to evaluate the accuracy of cow performance predicted by FNIR-NutBal, FNIR-NutBalPro and FOR-NRC systems. Initial BW, body condition score (BCS), hip height and breed were used to establish cow biotypes for prediction programs. Every 28 d, cow BW and BCS were measured and forage and fecal samples collected. Weather data, cow status and FOR or FNIR results were entered into NutBal, NutBalPro and NRC programs. Forage CP estimated by FNIR (CPFNIR) or FOR (CPFOR) were similar. In trials 1 and 2, correlation coefficients between CPFNIR and CPFOR were r = .24 and r = .43, respectively. Forage TDN estimated by FNIR was greater (P <.05) and lowly or moderately correlated to FOR estimates. Actual BW change between weigh periods (BWCHG) and ADG were similar to NRC predictions, but less (P<.0001) than predicted by NutBal or NutBalPro. The NutBal or NutBalPro mean BCS change between weigh periods (BCSCHG) were greater (P<.001) than NRC or Actual BCSCHG. Actual and NRC BCSCHG were similar (P>.2, trial 1) or tended (P<.1, trial 2) to be similar. Cow performance estimated by NRC was highly correlated to Actual. Absolute differences in animal performance were also investigated for each prediction program. In trials 1 and 2, NutBal and NutBalPro over-predicted BWCHG, ADG and BCSCHG by 40 kg, 1.25 kg/d and .75 BCS, respectively, compared to actual cow performance. It appears that FNIR is a promising predictor of forage CP but not TDN. Also, the FOR-NRC is a satisfactory predictor of cow performance.
Master of Science

Thesis (M.S.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 20, 2009) Includes bibliographical references.

A series of four trials over the grazing season were conducted to evaluate the nutritional status of beef cows grazing reclaimed strip-mined pastures in southwestern, Virginia. Blood samples, esophageal fistula forage samples and hand plucked forage samples were taken in each trial. An external marker, Ytterbium, and an internal marker, indigestible neutral detergent fiber (INDF) were used to estimate organic matter intake, fecal output and digestibility. In addition to samples taken during the trials, blood samples and hand plucked forage samples were taken monthly for 11 mo prior to the trial period. In late summer esophageal masticate samples had a low fiber fraction (ADF and NDF), high crude protein and total nonstructural carbohydrates (TNC) which contributed to a high organic matter digestibility. Hand plucked forage samples had higher TNC than esophageal masticate samples. Organic matter digestibility predicted by the internal marker was highest in late summer 61.6%, similar in spring and late fall, and lowest in mid-summer, 52.6% (p < .01). Fecal output was highest in mid-summer and lowest in spring (p < .05). Estimated intake was not significantly different in any of the trials. Although data was variable, forage quality was higher in May, June, October and November samplings, as indicated by highest CP, TNC, and lower NDF and ADF values, compared with July and August data when forage quality was lowest. Packed cell volume, BUN and serum P and Mg concentrations fell within normal ranges for beef cattle. Low BUN values were observed in spring and late fall which corresponded to low crude protein values observed in the esophageal masticate samples for the same trials. Serum Cu was on the low end of normal values in the late spring and decreased to .6 ppm by late fall. Serum K levels were above the expected values for beef cattle. Serum Na concentrations were lower than normal with lowest values observed throughout spring and summer months.
M.S.

Tall fescue is a widely grown, cool season grass prevalent in the eastern United States that is known for its resistance to abiotic and biotic stresses. A main reason for tall fescue's resistance to these stresses is attributed to the presence of a fungal endophyte. Unfortunately, this endophyte also adversely affects cattle production. Cows consuming the ergot alkaloids produced by these endophytes can exhibit decreased feed intake, growth performance, organ vasoconstriction, and increased rectal temperature. This work is interested in examining how endophyte toxin exposure impacts pregnancy in cattle. Reduced blood flow to the fetus and inadequate maternal nutrition contributes to intra uterine growth restriction (IUGR), and this work proposed that fescue endophyte toxicity affects the gestating cow and fetus. Three studies were completed. In experiment 1, gestating cows grazed high or low endophyte fescue pastures during late gestation to determine if exposure to ergot alkaloids in utero results in IUGR and if calves from these pregnancies have altered growth performance. Creep feeding was evaluated as a mitigation strategy for impaired calf growth due to fescue toxicity, and feedlot performance was evaluated to determine if consuming fescue during gestation and creep feeding would affect feedlot performance. Calf BW was different (P < 0.01) by treatment x time. Birth weights of calves were similar , prior to creep feeding calves exposed to high endophyte fescue were lower, and post-supplementation creep fed calves had increased BW. Days on feed and dressing percentage were decreased in the supplemented group, and marbling score was decreased for both the supplemented and unsupplemented groups following the completion of the feedlot phase (P < 0.05). The second study was setup similar to study one, however cows were exposed to fescue pastures from d 170 of gestation until calving. Calf birth weights did not differ, but weights were increased in the supplemented group post creep feeding (P < 0.05). Average daily gains (ADG) of supplemented calves were greater during the supplementation period (P < 0.01). In the third study, indwelling vaginal temperature probes were used to evaluate differences in body temperature of cows fed fescue seed with high or low levels of ergot alkaloids during early gestation, and in varying environmental conditions. In the winter trial, body temperature was measured hourly from days 0-14 of gestation. In the summer trial, body temperature was measured hourly from days 0-32 of gestation. Body temperatures were different (P < 0.01) between treatments during both trials.
Master of Science

Overwintered, gestating beef cows fed low-quality forage are at risk of nutrient restriction which can lead to compromised growth and poor carcass quality in their offspring. In many species, poor maternal nutrition also results in reduced uteroplacental hemodynamics and fetal growth. To better understand how different nutritional paradigms influence the beef cow, our lab has examined the impacts of nutrient restriction and diet composition on uterine hemodynamics. Previous research suggests that dietary intake or protein supplementation alone does not increase uterine blood flow. The current study examined the effects of dietary starch supplementation and our findings indicate that increasing starch composition of the diet does not alter uterine hemodynamics or fetal growth. Perhaps, a more successful feeding strategy could include a balanced protein to energy ratio and ad libitum access to forage, allowing the cows to increase intake without the substitution effect documented in this study. These ideas merit further investigation.

Doctor of Philosophy
Department of Animal Sciences and Industry
KC Olson
The objective of this series of studies was to develop and improve methods of production in cow/calf operations of the Great Plains. Ultrasound measures of longissimus muscle depth (LMD) and intramuscular fat (IMF) of Angus × heifers were used to predict lifetime cow productivity. IMF and LMD were categorized into high, medium, and low groups (IMFG and LMDG, respectively). Cows in the high and medium LMDG had greater (P < 0.05) pregnancy rates than cows in the low LMDG. Calf BW at weaning increased (P < 0.05) as dam IMF increased. Angus crossbred cows grazing native range were used to evaluate the effects of pre-partum ruminally-protected choline (RPC) supplementation on postpartum beef cow and calf performance. Under the conditions of our study, RPC supplementation had minimal (P > 0.05) effects on pregnancy rates and performance of beef cows and calves. Lactating crossbred cows with calves and non-pregnant, non-lactating Boer-cross nannies were used to evaluate the effects of co-grazing on herbivory patterns and animal performance while grazing native tallgrass rangeland infested heavily by sericea lespedeza (SL). The proportion of individual SL plants that had been grazed at the end of the trial was greater (P < 0.01) in co-grazed pastures than in single-species pastures. Grazing cows and goats in combination increased (P < 0.01) grazing pressure on SL without negatively affecting beef cow performance, beef calf performance, or residual forage biomass. Angus × cows and heifers grazing native range were used to evaluate the effects of pre-partum corn steep liquor supplementation on postpartum beef cow and calf performance. Under the conditions of our study, CSL supplementation did not generally promote beef cow and calf performance that was equivalent to supplementation with an isonitrogenous, dry, corn-soy alternative. Cow calf pairs were used to evaluate the effects of grazing system (GS) and stocking rate (SR) on cow and calf performance. Late season rest-rotation (LSRR) was compared with continuous (CONT) grazing at low, moderate, and high SR. Under the conditions of our study, CONT produced consistently better (P < 0.01) late-season cow and calf performance than LSRR. Season-long effects of SR on animal performance were minimal; moreover, GS and SR treatments produced equivalent pregnancy rates.

The objectives of the current study were: 1) to examine serum bPAG concentration during pregnancy, and in the post-partum period in relation to the overall nutritional and metabolic status and post-partum anoestrous period; 2) to investigate bPAG decay models for postulating distribution and metabolism of bPAG in the blood circulation using half-life (t1/2) and to compare the t1/2 values between breeds and nutritional treatments for the clearance of bPAG; 3) to examine the suitability of the radioimmunoassay (RIA) for measuring bPAG in urine, saliva and milk, to investigate temporal relationships between bPAG in these fluids and that in the serum, and to assess the potential of bPAG in these fluids for pregnancy diagnosis in cows. Estimation of total bPAG disappearance from plasma per day during week 1 post-partum did not differ between the breeds. Urinary bPAG, over the same period of time, was lower for Welsh Black than Simmental and Charolais cows (0.45 vs 0.53 and 0.59 nmol (s.e.d 0.03) p<0.05) but not for Aberdeen Angus cows (0.48 nmol); bPAG in saliva was lower for Welsh Black than Charolais and Aberdeen Angus cows (1.65 vs 2.42 and 2.49 nmol (s.e.d 0.11) p<0.05) but not for Simmental cows (1.44 nmol/1), and bPAG measured in milk (whole) was lower for Charolais than Simmental cows (0.26 vs 0.47 nmol (s.e.d 0.06) p<0.05) but not for Aberdeen Angus (0.38 nmol/1) and Welsh Black cows (0.37 nmol/1). Total body elimination of bPAG in urine, saliva and milk accounted only for 5.28 % of the total plasma bPAG. Total body elimination of bPAG in urine, saliva and milk accounted for only 5.28 % of the total plasma bPAG. The remaining 94.72 % of bPAG may have been metabolished and was undetectable by the current RIA technique. A theoretical assessment for potential use of bPAG RIA for pregnancy diagnosis using urine, saliva and milk showed that the minimum detection limits of measuring bPAG in these fluids were reached and / or exceeded by Day 200 of gestation, or later. Consequently, assay of bPAG in these fluids for early pregnancy diagnosis would not be appropriate unless the sensitivity of the assays is improved considerably, or prior assay sample extraction/concentration is carried out.

Thesis (M.S.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains vi, 44 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 35-43).

Thesis (M.S.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains ix, 64 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 49-60).

Master of Science
Department of Animal Sciences and Industry
KC Olson
Our objective was to determine the effects of supplemental corn steep liquor (CSL) on voluntary selection of sericea lespedeza (SL) by beef cows grazing native tallgrass range. Dietary botanical composition of cows (n = 145; initial BW = 579 ± 91 kg) was evaluated during a 150-d grazing period (5/1 to 10/1). Native pastures (n = 9; 50 ± 17 ha) infested by SL (average SL biomass = 37% of total forage biomass) were assigned randomly to 1 of 2 treatments: grazing by unsupplemented cows or grazing by cows supplemented with CSL (1.79 kg DM • cow-1 • d-1; 45% DM, 34% CP). Cows were assigned randomly to treatment and pasture (stocking rate = 0.5 ha/AUM). Concentration and protein-binding capacity of condensed tannins (CT) in SL were measured monthly. Fecal samples were collected from each cow on 6/1, 7/1, 8/1, 9/1, and 10/1. Herbivory of SL was estimated along line transects in October. Plant fragments in fecal samples were quantified via a microhistological technique; fragment prevalence in fecal material was assumed to equal botanical composition of the diet. Concentration and protein-binding capacity of CT in SL were greatest (P < 0.01) on 8/1 and 9/1, respectively. The proportion of individual SL plants showing evidence of herbivory tended to be greater (P = 0.09) on pastures grazed by supplemented cows compared to pastures grazed by unsupplemented cows (94 vs. 80% of SL stems, respectively). Prevalence of SL in beef cow diets was influenced (P < 0.01) by CSL supplementation and by month. Prevalence of SL in beef cow diets was not different (P ≥ 0.35) between treatments when concentration and protein-binding capacity of CT were relatively low (6/1, 7/1, and 10/1). In contrast, supplemented cows selected more (P < 0.01) SL than unsupplemented cows when concentration and protein-binding capacity of CT were greatest (8/1 and 9/1). We interpreted these data to suggest that voluntary selection of SL by beef cows was inversely related to concentration of CT; moreover, supplemental CSL stimulated voluntary selection of SL during periods of high CT concentration. Supplemental CSL did not influence selection of other plant species that were monitored.

Experiments were designed to assess the effects of energy and protein intake on metabolic function and reproductive efficiency in single and twin suckling beef cows and heifers. A role was proposed for endogenous opioid peptides in mediating the effects of photoperiod, suckling and nutrition on anterior pituitary hormone release, and tested with respect to nutrition. The first two experiments were designed to quantify the effects of pre- and post-partum energy and protein intake, on milk yield and composition, body tissue mobilisation, the post-partum anoestrous interval, and subsequent conception rates to artificial insemination and embryo transfer in single- and twin-suckling beef cows. Cows very quickly adjusted their metabolism and level of performance to be in line with their current level of energy and protein intake. Ovulation and the resumption of normal oestrous cycles occurred soon thereafter. The third experiment tested the hypothesis that post-partum energy and digestible undegradable protein (DUP) intake can influence hypothalamic opiodergic tone and the ability of the anterior pituitary to secrete luteinizing hormone (LH), prolactin and growth hormone in response to naloxone (an opioid receptor antagonist) challenge. Results indicated that high energy diets allowed cows to overcome the opioid mediated block on LH release and resume oestrous cyclicity earlier than cows on low energy diets. High levels of DUP increased the opioid mediated block on LH release. The final experiment examined the interactive effects of body condition and energy intake on hypothalamic opioidergic tone and pituitary responsiveness, in terms of LH release, when challenged with an exogenous source of gonadotrophin-releasing hormone (GnRH). Naloxone was unable to evoke consistent LH responses in this experiment but the LH response to GnRH was influenced by both body condition and energy intake. In conclusion opioid peptides may provide a means by which certain homeostatic regulators interface with homeorhetic hormones released from the anterior pituitary gland.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 6, 2009) Thesis advisor: Dr. David J. Patterson, Includes bibliographical references.

We hypothesized that global maternal nutrient restriction during early and mid-gestation followed by realimentation in pregnant beef cows would alter placental arterial vascular function. We tested changes in placental caruncular (CAR) and cotyledonary (COT) arterial sensitivity to bradykinin (BK), a potent vasodilator. Cows were randomly assigned to be nutrient restricted for 55 or 110 during early to mid pregnancy. On d 85, 140, and 254 cows were euthanized and CAR and COT arteries were isolated. Maternal nutrient restriction during early and mid-gestation allowed for placental compensation to overcome the loss of nutrients while realimentation returned placental arterial vosoactivity similar to control cows in response to BK. Further, CAR and COT placental arteries may respond to BK induced vasodilation through different pathways which is important when considering possible therapeutics for compromised pregnancies.

Two experiments investigating impacts of maternal nutrition in beef cows were conducted; 1) to test the impact of duration of global nutrient restriction and subsequent realimentation throughout gestation on placentome capillary development; and 2) to test the response of protein supplementation on blood flow to the uterus and mammary gland in late gestation. In experiment one, realimentation following varying periods of nutrient restriction had minor alterations in angiogenic factor mRNA expression of as well as vascularity in the placentome. In experiment two, mammary gland blood flow was not affected, while protein supplementation decreased uterine blood flow. Calf birth weights were not influenced by maternal dietary treatment. Results of these studies are important when considering nutritional management of cows during gestation. Further research is warranted to investigate capillary function to determine how compensation is occurring when vascularity is not being drastically compromised with global maternal dietary restriction. Additionally the mechanism of how DDGS supplementation is decreasing blood flow to the uterus is a question which requires more exploration.

The objective of this experiment was to determine if bull exposure influences follicular wave dynamics in primiparous, postpartum, anestrous, suckled, beef cows exposed to bulls. In Experiment 1, cows were exposed (continuously 24 h/d), (EB; n = 5) to bulls or not exposed to bulls (NE; n = 5) throughout the experimental period. In Experiment 2, cows were exposed to bulls for either 12 h, (EB12; n = 15), 6 h, (EB6; n =14) or not exposed to bulls (NE; n = 10) from the start to the end of the experimental period. In Experiments 1 and 2, cows were 67 d ± 3.8 (mean ± SE) and 51.5 ± 2.3 d postpartum at the start of the experiment. Follicular characteristics of each cow were examined by transrectal ultrasonography. In Experiment 1, interwave interval for wave 3 was shorter in EB than NE cows. Maximum dominant follicle (MDF) diameter tended to be greater during wave 2 for EB than NE cows, while wave 3 was greater for EB than NE cows. However, MDF diameter for wave 6 was greater for NE than EB cows. In Experiment 2, EB12 cows had fewer follicular waves to the resumption of luteal activity (RLA) than NE cows, while the number of waves to RLA for EB6 cows did not differ from that of EB12 or NE cows. Normalizing follicular waves to the time of RLA for cows within the EB12 and EB6 indicated that those cows at RLA had larger MDF diameters for the wave that produced the ovulatory follicle than cows that did not RLA. These data show the effects of bull exposure in altering follicular growth and developmental patterns, shortening the inter-wave interval and increasing the MDF diameter. Though the mechanism through which bull exposure alters postpartum follicular development is not entirely understood, these data provide new understanding.

Three experiments were carried out to assess the energy and protein requirments of single and twin-bearing beef cows during the last three months of pregnancy and also to observe the effects of pregnancy nutrition on the subsequent lactational performance of cows and calves. A wide range of energy level was applied to single and twin-bearing cows. As assessed from body weight change, calf birthweight, milk yield, calf growth rate and blood parameters, it was found that there was no benefit in giving high levels of dietary energy to cows during pregnancy. It was concluded that feeding 50 and 70 MJ ME/day to single and twin-bearing cows respectively together with a high proportion of UDP may be acceptable levels during the latter part of gestation, provided that the cows are in good body condition at the start of the last trimester of pregnancy and they are given adequate nutrition during early lactation. Another three experiments were conducted with pregnant ewes, wethers, pregnant heifers and steers to measure the digestibility and to determine the metabolisable energy value of two mixed diets which differed in rumen degradability of protein. Such diets were used in experiments with pregnant cows. A comparison was made between the digestive capacity in different species and sex of animals. Digestibility co-efficients of two diets, two sexes and two species did not differ significantly. Therefore, it was concluded that metabolisable energy value determined for mixed diets using sheep can be used for cattle. ME value of mixed diets was less than that calculated in these experiments but the extent of the decrease may be acceptable under farm conditions.

Cattle ranchers are periodically faced with the decision of whether or not to cull/replace a brood cow. Assets such as beef cows are subject to stochastic elements that affect the cull/replacement decision. Stochastic elements include events such as death, infertility, and the inability to meet specific performance standards. Observations suggest that many Montana ranchers use a period-by-period cull/replacement decision-making strategy. However, varying management practices, stochastic elements, and the lengthy biological process associated with cattle production limit the validity of a single long-run replacement policy applied across all cattle ranches. This thesis examines a long-run optimal replacement policy based on economic criterion that individual cattle ranchers can adapt to their specific operation. Burt's discrete time model for optimal replacement under stochastic conditions is used as the analytical model. Published data measuring the likelihood of stochastic events, Billings, Montana cattle prices, and the long-run average variable costs from a case study of an individual ranch in Eastern Montana are used in the empirical model. Prices and costs are varied to reflect varying cattle prices over time and the heterogeneous nature of management practices with respect to costs. The results indicate that, although a single optimal planned replacement age is not derived, voluntary replacement should occur between cow ages of six and eleven years. These results are insensitive to varying price/cost combinations used in the study. Given the insensitivity of the results to the varying price/cost levels it is likely that the probabilities measuring the stochastic events are the main determinants in deriving an optimal replacement age. The results also show that cattle ranching is profitable except in high cost with average to below average model price conditions.

The production environment is known to have a large influence on extensively managed beef cows. A better understanding of the relationship between the beef cow and her environment should be useful in the pursuit of improving beef cow efficiency. The influence of the production environment on the efficiency of extensively managed Bonsmara cows was investigated through a series of research objectives. It was found that VEGMAP’s bioregion classification system can be used to describe the South African beef production regions. The environmental characteristics with the potential to influence beef cow efficiency were identified as temperature, rainfall, cation exchange capacity, soil pH, soil organic carbon, soil P and grazing capacity. A dataset was created that contains the historical cow production records for every Bonsmara breeder. GIS tools were then used to link the cow production records with the production region in which the farm is located, as well as the environmental characteristics for that specific location. The combined dataset was then statistically analysed to investigate the research objectives. The influence of the geographic location, production region and breeder on Bonsmara production traits was investigated by cluster analysis and ANOVA. Results from ANOVA indicate that production region has a statistically significant (p < 0.05) influence on production traits. The influence of the breeders on the same production traits was, however, statistically much larger (p < 0.0001) than production region. Bonsmara production traits are therefore influenced to a greater extent by the breeders rather than production environment. Stepwise regression analysis was used to determine the influence of the combined environment on production traits. The combined environment has a statistically significant (p < 0.0001) influence on all the production traits. The results indicate that the extent of the influence of the environment on production change through the growth curve. The environment’s influence was the greatest at weaning (9%) and yearling age (10%). Bonsmara weaning and yearling weights therefore show the largest potential for manipulation through management. The influence of individual environmental characteristics on all the Bonsmara cow production traits was then investigated by the same stepwise regression analysis. Most of the environmental characteristics were found to have a statistically significant (p < 0.0001) influence on the production traits. Rainfall and temperature had the largest influence on Bonsmara production traits. The negative influence of rainfall was attributed to the influence of rainfall on the quality of the grazing. The influence of temperature on production traits was small. The small negative influence of temperature could indicate that Bonsmara cows are well adapted to the main South African beef production regions. Finally, the relationship between Bonsmara cow size and reproduction was investigated by linear regression analysis. Results indicate that larger Bonsmara cows are to some extent more reproductive than smaller cows. The study confirmed that production environment influences beef cow efficiency. Bonsmara breeders however have a much larger influence on the efficiency of their cows through the implementation of management practices and breeding objectives.
Dissertation (MSc(Agric))--University of Pretoria, 2012.
Animal and Wildlife Sciences
unrestricted

Two experiments tested the efficacy of gonadotropin-releasing hormone (GnRH) or estradiol cypionate (ECP) administration in combination with controlled internal drug release (CIDR) inserts on pregnancy rate to fixed-time artificial insemination (FTAI) in beef heifers. In the first experiment, heifers in the two ECP groups received ECP in conjunction with the CIDR insert. The CIDR insert was removed and PGF was administered on either d 7 or 9. Heifers received ECP 24 h after CIDR removal and were inseminated 30 h after ECP. Heifers in the two GnRH groups received GnRH in conjunction with the CIDR insert. Heifers received PGF on either d 6 or 7, and the CIDR insert was removed on d 7. Heifers were inseminated and received GnRH 48 h after CIDR removal. Pregnancy rates to FTAI were higher for heifers treated with GnRH. Pregnancy rate to FTAI was highest for heifers in the GnRH group that received PGF on d 6 and was lowest for the group that received ECP in combination with a 7-d CIDR insert. In the second experiment, heifers received GnRH in conjunction with the CIDR insert. CIDR inserts were removed and PGF was administered on d 7. Heifers were inseminated 60 h later, with one group receiving GnRH at insemination. Pregnancy rate to FTAI was higher for heifers that received GnRH at insemination. The final experiment tested the efficacy of estradiol 17_ (E17) or GnRH in combination with a CIDR insert on pregnancy rate to FTAI in Brahman cows. Either E17 or GnRH was administered in conjunction with the CIDR insert. CIDR inserts were removed on d 7. Cows in the GnRH group received PGF on d 6 and GnRH at insemination which occurred 48 h after CIDR removal. Cows in the E17 group received PGF on d 7, E17 24 h later, and were inseminated 30 h after E17 administration. Pregnancy rate to FTAI was higher for cows treated with E17. These data indicate acceptable pregnancy rates were obtained when the CIDR insert was combined with either GnRH in beef heifers or with E17 in Brahman cows.

Postpartum LH and GH secretory patterns were evaluated with mature Brangus cows group fed either 50%M (n = 8) or 100%M (n = 7) NRC maintenance energy requirements starting two months prepartum and continuing for three months postpartum. Feed level was adjusted at 14 day intervals. Weights of cows and (or) calves were taken every 14 days before and after calving. Sequential blood samples were taken every 15 min for 8 h at biweekly intervals starting 14 days postpartum and continuing until 100 days. Serum LH and GH were determined by a validated double antibody RIA. A peak-detection algorithm was used to summarize hormone data into 5 variables for each cow at each bleeding period. Data were analyzed by GLM and regression using SAS procedures. Cows in the 100%M group were heavier (P<0.01) at calving time and at the end of the trial. There were no significant differences for weight of calves at birth or at the end of the study for the two energy levels. Total release of LH during secretory episodes was 5 fold greater (27 vs 5 ng/ml x min P<0.05) in cows receiving 100%M vs 50%M energy. Basal concentration and peak height of LH increased linearly with time postpartum in 50% but not 100% energy groups. For GH, cows receiving 50%M energy had more secretory spikes (2.6 vs 2.1 per 8 h; P<0.05), and higher basal concentration (14 vs 8 ng/ml; P<0.05), and a shorter duration of secretory episodes (82 vs 95 min; P<0.05) compared with cows on 100%M energy. Maximum release of GH occurred earlier postpartum in cows receiving 100%M energy (30-39 d) vs cows receiving 50%M energy (90+d). Number of GH peaks increased linearly with time postpartum in cows on 100% energy, but not in the 50% group. Dietary energy restriction of mature beef cows significantly alters several parameters of LH and GH secretion during the early postpartum period.

Nutrition and suckling are known to be the most important factors affecting the length of the anovulatory post-partum period in beef cows. In sheep, nutrition and suckling are also important factors when ewes lamb during the season breeding, in more intensive production systems. A number of neurotransmitters have been proposed to be implicated in the activation of the GnRH pulse generator, which controls LH release. The aim of the present study was to investigate the role of the opioid peptides in the mediation of the effects of nutrition and suckling in both cows and ewes, during the post-partum period. Experiment 1 was designed to quantify the effects of post-partum energy intake on post-partum cows. Sixteen Aberdeen Angus and Simmental cows were arranged in a 2x2 factorial, with breed and energy intake as main factors. An opioid peptide antagonist receptor (naloxone) was administered in all cows in two periods of the post-partum (week 4 and 7) and in two consecutive days, in a high (0.8 mg/kg) or a low (0.4 mg/kg) dose. The overall response in LH to naloxone was low, and there was no significant treatment effects. However, a higher opiodergic tone at early, compared with at late, post-partum period was observed. Naloxone failed to evoke any prolactin response. Experiment 2 was designed to investigate the effects of nutrition and suckling intensity on the post-partum of ewes lambing during their breeding season, and to quantify these effects on the opioidergic tone. The experiment involved 40 ewes, in which 32 were assigned to two different diets and all of them suckled, and 80 ewes were assigned to one of these two diets and were weaned. All ewes were challenged with naloxone at day 12 post-lambing, with either a low (0.7 mg/kg) or a high (1.4 mg/kg) dose. Naloxone evoke an LH response in most of the animals, irrespective of the diet in which they were assigned. Naloxone also evoked an LH response in either suckled or weaned ewes. In the experiment 3, the interactive effect of nutrition and suckling on the post-partum interval and opioidergic tone was investigated. Sixteen Simmental cows were involved in a 2x2x2 factorial, with body condition at calving, post-partum energy intake and suckling intensity as main factors. At week 4, naloxone was administered (0.8 mg/kg) when a new follicular wave was detected and the follicle was in a growing stage, and it was also administered using the same dose, when that follicle achieved the dominant phase.

Exposing cows to bulls or excretory products of bulls stimulates resumption of ovarian cycling activity in postpartum, suckled, anestrous cows. This biostimulatory effect may be mediated by pheromones produced by bulls that stimulate physiological changes in metabolic regulation of the hypothalamic-pituitary-ovarian (HPO) axis of cows. In Experiment 1, the hypotheses tested were that concentrations of glucose, NEFA, thyroxine (T4), tri-iodothyronine (T3), and T3:T4 ratios do not differ between cows exposed to bulls or steers. The biostimulatory effect of bulls was associated with lower mean concentrations of NEFA in postpartum cows. Experiment 2 was designed to determine if continuous (24-h daily) bull exposure alters temporal patterns of leptin concentrations in postpartum, anestrous cows. Cows exposed to bulls that resumed cycling activity after the start of the experiment tended to have higher leptin concentrations by the end of the 30-d exposure period than cows not exposed to bulls. However, it was not known if these changes were related to resumption of ovarian cycling activity in postpartum, anestrous cows. Experiment 3 tested the hypothesis that temporal leptin concentrations may depend upon duration of daily bull exposure. Cows had higher daily leptin concentrations and resumed ovarian cycling activity sooner as duration of daily bull exposure increased. In conclusion, as duration of daily bull exposure increases, the biostimulatory effect of bulls alters temporal leptin concentrations and this change may facilitate or support the function of the HPO axis and accelerate resumption of ovarian cycling activity in primiparous, postpartum, suckled, anestrous cows.

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xvii, 181 p. : ill. Includes bibliographical references (p. 159-181). Available online via OhioLINK's ETD Center

To investigate the effects of corn dried distiller?s grains plus solubles (DDGS) supplementation to cows during late gestation, 27 multiparous beef cows were divided randomly into 2 treatment groups (CON; n = 15; SUP = DDGS at 0.3% of BW; n = 12). Supplemented cows gained BW (P < 0.01) while CON cows tended to lose BW (P = 0.06). A main effect of treatment (P = 0.02) and day (P < 0.01) was observed for total uterine blood flow (BF). Calves born to SUP cows tended to be heavier than calves born to CON cows (P = 0.06). Both groups gained (P < 0.01) BW with advancing lactation. Supplementing DDGS altered voluntary feed intake, cow body maintenance, uterine and mammary blood flow, and calf weaning weights. Results suggest an influence on overall maternal metabolism and nutrient flux to the fetus.

This 2-yr experiment evaluated productivity of wild-type, endophyte-infected tall fescue (E+) and novel endophyte-infected tall fescue (NE) summer stockpiled (SS) pastures and the performance of fall-calving beef cow/calf pairs stocked on each cultivar. Fescue cultivars used were KY-31 and MaxQ for E+ and NE treatments, respectively. Pregnant Simmental x Angus cows (128 total, 64 each yr) were stratified by BW, BCS, and expected calving date and then allotted to 1 of 10 pasture groups within each yr (20 groups total, 10 per treatment). Forage growth was stockpiled from April until the initiation of strip-grazing on August 31 of 2017 and 2018. Cows grazed treatment pastures for 52 d from 23 ± 14 d prepartum to 29 ± 14 d postpartum, and calved on treatment pastures. Forage quadrats were clipped from the grazed and ungrazed portions of each pasture to determine weekly forage mass. Total ergot alkaloid (TEA) concentrations were analyzed for all pastures at the beginning of the experiment and every subsequent 2 wk for E+ tall fescue. Cow BW was recorded on 2 consecutive d and BCS determined at the start and end of the experiment. In yr 2, ultrasound 12th rib fat thickness (FT) was measured at the beginning and end of the treatment period Milk production was estimated using the weigh-suckle-weigh technique at 29 ± 14 d postpartum. Initial TEA concentrations for NE (Yr. 1 = 112 µg/kg; Yr. 2 = 632 µg/kg) were decreased (P ≤ 0.01) compared to E+ (Yr. 1 = 1831 µg/kg; Yr. 2 = 2903 µg/kg). TEA concentrations for E+ pastures did not differ (P < 0.23) by sample date. However, average TEA concentrations were greater for yr 2 than yr 1(P ≤ 0.01). Fescue cultivars were not different (P ≥ 0.06) in forage CP, Ash, Ether Extract, and grazed or ungrazed forage mass. However, differences were observed (P ≤ 0.02) for ADF, NDF, and TDN by fescue cultivar. Cow BW, BCS, and FT at the beginning and end of grazing were not different (P ≥ 0.41) by treatment. Milk production was greater (P < 0.01) for cows grazed on E+. Calving date, calf BW, calf ADG were not different (P ≥ 0.65) by treatment. Neither AI nor overall conception rates differed (P ≥ 0.23) between cultivars. Performance of fall-calving cows pre-exposed to E+ was not hindered when grazed on E+ relative to NE in a SS system.
Master of Science
Wild-type, endophyte-infected tall fescue (E+) is the predominant forage of use for producers within the southeastern United States. Endophyte-infected tall fescue gained notoriety due to its drought and pest resistance as well as climate adaptability. These advantages are the result of a symbiotic relationship with an endophytic fungus that has been shown to decrease in animal performance through the production of toxic ergot alkaloids. Development of improved fescue cultivars provided producers with an alternative forage, known as novel endophyte-infected tall fescue (NE), that maintains the agronomic advantages noted with E+ fescue without negative impacts on animal gain and reproductive performance. In adopting NE tall fescue, producers are faced with the financial challenge of renovating existing stands of E+ with NE fescue; leaving pastures unusable during times of normal grazing behavior. This constraint has highlighted the need to explore forage utilization and strategies that can extend the grazing period that do not require the significant cost of total renovation with NE. Fall stockpiled tall fescue has provided producers an option to extend grazing from late November through February when pasture growth ceases and hay supplementation is normally needed. However, a 60 to 90 d period between summer and fall stockpiled grazing leaves producers looking for an additional strategy to provide standing forage for their herds. Summer stockpiling (SS), is a novel grazing strategy that bridges summer and fall stockpiled grazing through proper accumulation of 25 % of total pasture to help extend producers grazing season. The objective of the current experiment is to evaluate both E+ and NE SS pastures and its effect on animal performance, forage availability, and nutritive value. Cow BW and BCS were measured at the initiation, conclusion, and before artificial insemination. Calf BW and ADG were assessed 48 h post-calving and at weaning. Ungrazed and grazed forage mass was collected weekly, while measurements of ADF, NDF, CP, TDN, ether extract, and ash were measured every 2 weeks. After a 52 d treatment period, forage mass was similar across both cultivars, with ADF, NDF, and TDN favoring E+ tall fescue. Additionally, animal performance across both E+ and NE pastures were similar, however increased milk production was observed for cows grazed on E+. This experiment helps shed light on the concept of strategic renovation. Strategic renovation can be best utilized by producers who are interested in maximizing pasture utilization through rotationally grazing E+ and NE tall fescue pastures. By following this renovation strategy, proper allocation of NE tall fescue during times of enhanced ergotism and E+ tall fescue during low thresholds will develop a more specific rotation thus decreasing renovation costs for producers when ergotism is lowest.

The cattle shown from 1981 to 1984 at the American Angus Breeders' Futurity were studied to determine the relationship between linear measurements and the judge's subjective placings. Linear measurements taken prior to the showing included wither height, hip height, and body length for both bulls and heifers. In addition body weight and scrotal circumference were recorded for bulls. A total of 624 cattle were studied-- 407 heifers and 217 bulls. The cattle were divided into five groups by age and sex to analyze the annual difference in means and standard deviations for all recorded measurements. Among all five groups of cattle, hip height increased at the fastest rate from 1981 to 1984. All measurements had a positive increase except body weight and scrotal circumference. The older bulls decreased by 61.67 lbs. in weight from 1981 to 1984 and decreased by 1.78 in. in scrotal circumference between 1983 and 1984. Coefficients of correlation were obtained using the recorded measurements along with age for all five groups. Wither height showed the closest association to other measurements. Among all five groups body length had the most inconsistent association to other measurements, primarily due to difficulty involved in obtaining an accurate body length measurement. Spearman's coefficient of rank correlation was conducted to determine which measurements the judges were giving most emphasis in the showring. It seems apparent that judges are continuing to select for larger framed cattle, placing greater emphasis on wither and hip height measurements and lesser emphasis on body weight and scrotal circumference. The findings in this study support the fact that judges are selecting for larger framed, later maturing cattle with little if any selection being placed upon present weight or indicators of future reproductive performance.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
Para a composição desta tese foram elaborados três artigos científicos baseados em estudos realizados com matrizes da raça Nelore e suas respectivas crias, submetidas a diferentes estratégias de suplementação em diferentes fases de produção. No estudo descrito no primeiro artigo, objetivou- se avaliar a influência da utilização de suplementação múltipla no pré e/ou pós- parto, para matrizes Nelore em boa condição nutricional, sobre o desempenho de suas progênies durante a fase de cria. Oitenta e quatro matrizes pluríparas da raça Nelore (peso corporal de 522 ± 9 kg e escore de condição corporal (ECC) de 5 ± 0.08, numa escala de 1-9) e suas respectivas crias (44 fêmeas e 40 machos) foram utilizadas. Os tratamentos das matrizes foram: 1 kg (matéria natural) de suplemento durante 90 dias pré-parto e 90 dias pós-parto (suplementação o tempo todo), 1 kg de suplemento (matéria natural) durante 90 dias pré-parto e mistura mineral após o parto (suplementação antes do parto), mistura mineral no período pré-parto e 1 kg de suplemento (matéria natural) durante 90 dias pós-parto (suplementação pós-parto) e tratamento controle, recebendo apenas mistura mineral no período avaliado (Controle). As matrizes que foram suplementadas antes do parto, pariram bezerros mais pesados que aquelas que receberam suplemento apenas no período pós-parto. Também não foram identificadas diferenças para peso corporal (PC) dos bezerros no desmame, ECC e produção de leite das matrizes, entre os diferentes tratamentos (P > 0.05). Matrizes do tratamento controle apresentaram menor teor de gordura no leite na primeira coleta, em relação às suplementadas (P < 0.05). Os bezerros (apenas machos) filhos das matrizes do tratamento controle apresentaram maio (P < 0.05) consumo de matéria seca (CMS) que os filhos de matrizes suplementadas. Os tratamentos das matrizes não diferenciaram em relação à concentração de T3, T4, glicose, área de olho de lombo (AOL), espessura de gordura subcutânea (EGS), profundidade do Gluteus medius (PGM) e espessura de gordura na P8 (EGP8), nos seus respectivos bezerros. Bezerras, filhas de matrizes do tratamento Controle, apresentaram menor teor de glicose e maior teor de ureia no sangue, quando comparadas aquelas filhas de matrizes suplementadas. O uso de suplementação de matrizes, antes do parto proporciona o nascimento de bezerros mais pesados, e o não uso de suplementação para as matrizes no período pré e /ou pós-parto causa aumento do consumo de matéria seca dos bezerros na fase de cria. No segundo artigo o objetivo foi avaliar o efeito de diferentes esquemas de suplementação a pasto, sobre o desempenho e composição de carcaça de bezerros na fase de cria, assim como a influência destes esquemas de suplementação sobre o desempenho destes animais no período de confinamento. 48 bezerros da raça Nelore (147 ± 7 kg e três meses de idade) na fase de cria e suas mães (512 ± 9 kg e seis anos de idade) foram utilizados em um delineamento inteiramente casualizado. O período de suplementação foi de 142 dias, subdividido em dois períodos (1 e 2) de 71 dias, seguidos de um tempo de 125 dias de confinamento. Os tratamentos dados aos bezerros foram: fornecimento diário de 5 e 10g de matéria seca (MS) de suplemento/kg de PC nos períodos 1 e 2 respectivamente (5S/10S), 10 e 5g de MS de suplemento/kg de PC nos períodos 1 e 2 respectivamente (10S/5S), 7.5g de MS de suplemento/kg de PC em ambos períodos (7.5S) e mistura mineral ad libitum em ambos períodos (MM). Os bezerros suplementados apresentaram maior (P < 0.05) PC ao desmame e GMD durante toda a fase de cria, comparados aos animais do tratamento MM. Bezerros dos tratamentos 5S/10S e 7.5S apresentaram maior (P < 0.05) GMD e PC ao desmame, que bezerros do tratamento 10S/5S. Não foram observadas diferenças no GMD e PC entre os bezerros suplementados, durante o primeiro período. Os bezerros do tratamento MM apresentaram menor (P < 0.05) AOL, EGS, PGM e também menor PC no início do período de confinamento. Bezerros suplementados na fase de cria apresentam melhor desempenho ao desmame e tendem a apresentar maior peso ao final do confinamento. A quantidade de 7.5g de MS de suplemento/kg de PC/dia é recomendado para a otimização do desempenho de bezerros Nelore na fase de cria. No terceiro artigo objetivou-se avaliar o efeito dos diferentes esquemas de suplementação para bezerros na fase de cria, como descrito no artigo 2, sobre o comportamento dos bezerros lactentes e suas respectivas mães, assim como a influência dos diferentes esquemas de suplementação no desempenho das matrizes lactantes. Não foram identificadas diferenças (P > 0.05) em ECC, PC final e GMD das matrizes durante o período de avaliação. Bezerros do tratamento MM passaram mais tempo (P < 0.05) pastejando do que animais dos tratamentos 5S/10S e 10S/5S, no primeiro período avaliado. O tempo de mamada não diferenciou (P > 0.05) entre os bezerros de diferentes tratamentos, no primeiro período. Bezerros do tratamento 10S/5S passaram mais tempo (P > 0.05) mamando e menos tempo (P > 0.05) consumindo suplemento que os do tratamento 5S/10S, no segundo período. Mães de bezerros do tratamento MM apresentaram maior tempo de ócio e menor tempo de pastejo (P > 0.05), quando comparadas às mães de bezerros dos tratamentos 5S/10S e 10S/5S. Neste estudo foi concluído que diferentes esquemas de suplementação de bezerros a pasto, não afetam o desempenho de suas mães e que a suplementação diminui o tempo de pastejo destes bezerros.
For the thesis composition were prepared three scientific articles based on studies with dams of Nellore breed and their respective calves, submitted to different supplementation schedules in different phases of production. In the first article the objective was to evaluate the effect of Bos indicus dams’ supplementation in the pre and/or post calving period, on the performance of their male and female calves in the suckling phase. Eighty four pluriparous Nellore cows (body weight (BW) of 522 ± 9 kg and body condition score (BCS) of 5 ± 0.08 (1-9 scale)) and their calves (44 females and 40 males) were used. The dams’ treatments were: 1 kg of supplement during 90 days before and 90 days after calving (Supplemented all time), 1 kg of supplement during 90 days before calving and mineral mixture after calving (Supplemented before calving), mineral mixture before calving and 1 kg of supplement during 90 days after calving (Supplemented after calving) and a control treatment, receiving only mineral mixture ad libitum during entire experiment (Control). Cows supplemented before calving, calved heavier calves than supplemented after calving group. No differences were observed in BW at weaning, cows’ BCS and cow’s milk production (P > 0.05). Dams from the Control treatment had smaller milk fat in the first milk collection in the calves’ supplementation period, when contrasted with the supplemented groups (P < 0.05). Male calves of cows from the Control treatment showed higher (P < 0.05) dry matter intake (DMI) than sons of supplemented cows’ groups (average of DMI was: 5.5 kg and 3.4 kg to male calves of cows from Control treatment and cows which received supplement, respectively). No differences were found among the different dams’ treatments to T3, T4, glucose, rib eye area (REA), subcutaneous fat thickness (SFT), Gluteus medius depth (GMD) and P8 thickness fat (P8TF) of male calves. Daughters of cows from the Control treatment showed lower serum glucose, but had greater serum urea compared to daughters of supplemented dams. It was concluded that supplementation of cows before calving improves calves’ birth weight and the non-supplementation in the pre/post calving increase the male calves’ DMI during suckling phase. In the second article was evaluated the effect of different schedules of multiple supplementation on performance and carcass composition during the suckling phase of grazing Nellore male calves, as well as the influence of this supplementation schedule on performance of these animals in the feedlot. Forty-eight Nellore male calves (147 ± 7 kg BW and 3 months of age) in the suckling phase and their dams (512 ± 9 kg BW and 6 years of age), were used in a completely randomised design. The supplementation period was 142 days in duration and consisted of two equal 71 day periods (1 and 2), followed by a 125 days feedlot period. The treatments were: 5 and 10 g supplement dry matter (DM)/kg BW.day offered in period 1 and 2 respectively (5S/10S); 10 and 5 g supplement DM/kg BW.day offered in period 1 and 2 respectively (10S/5S); 7.5 g supplement DM/kg BW.day in both periods 1 and 2 (7.5S) and mineral mix ad libitum in both periods 1 and 2 (MM). Supplemented calves showed greater final BW and ADG (0.900 kg and 0.560 kg, the ADG in the suckling phase of supplemented and unsupplemented calves, respectively; P < 0.05), during the first and second experimental period. Calves from 5S/10S and 7.5S showed higher final BW and total ADG than calves from 10S/5S. No differences in ADG and FBW were observed in the first phase among supplemented calves. Animals from MM presented smaller (P < 0.05) rib eye area (REA), subcutaneous fat thickness (SFT) and Gluteus medius depth (GMD). In the feedlot period, supplemented animals had greater initial (P < 0.05) BW and tendency (P < 0.10) of greater final BW. It was concluded that male calves supplemented during the suckling phase, show better performance at weaning. The amount of 7.5 g supplement DM/kg BW.day is recommended to improve the performance. In the third article the aim was to evaluate different schedules of supplementation at pasture to calves in a creep feeding system, as described in the second article, on dam’s performance and behaviour of calves and their dams. No differences (P < 0.05) in BCS, final BW and ADG were found on dams’ performance. Calves from MM treatment spent more time (P < 0.05) grazing than supplemented calves from 5S/10S and 10S/5S treatments, in the first period. No difference in suckling time was found among the treatments (P > 0.05) in the first evaluated period. Calves from 10S/5S treatment spent more time suckling and less time eating supplements (P < 0.05) than 5S/10S treatment animals, in the second evaluated period. Dams of MM treatment’s calves showed more idle time and lower grazing time when compared with the mothers of calves from 5S/10S and 10S/5S treatments. It was concluded that, different schedules of Nellore calves’ supplementation at pasture, do not affect their mothers’ performance, and supplementation decreases grazing time of calves in the suckling phase.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
O presente estudo foi realizado para avaliar os efeitos da suplementação proteico- enegética e frequência de suplementação durante o pré (105 dias antes do parto) e pós- parto (105 dias após o parto) sobre o desempenho e características metabólicas de vacas primíparas de corte em pastejo. Foram utilizadas vinte e quatro vacas primíparas Nelore com PC médio de 409±8.0 kg, 22±0.9 meses de idade e 172±2.5 dias de gestação. Os tratamentos foram distribuídos aleatoriamente aos animais: Controle (mistura mineral ad libitum), Suplementação Diária (1.5 kg/dia de concentrado/animal) e Suplementação Infrequente (4.5 kg de concentrado/animal a cada três dias). O PC, GMD, ECC, esspessura de gordura subcutânea (EGS) e área de olho de lombo (AOL) foram avaliados no pré e pós-parto. Foram realizados dois ensaios de consumo e digestibilidade, o primeiro aos 55 dias antes do parto e o segundo, 55 dias após o parto. Amostras de sangue foram coletadas nos dias 27 e 9 dias antes do parto, ao parto, 9 e 27 dias após o parto para mensuração das concentrações de glicose, IGF-1, AGNE, -OH, colesterol e triglicerídeos, utilizados como indicadores do status energético, e mensuração de aminoácidos livres (AA), nitrogênio ureico sérico (NUS), proteína total, albumina e globulinas utilizados como indicadores de status proteico dos animais. As globulinas foram calculadas subtraindo a albumina quantificada do nível de proteína total. Aos 27 dias antes do parto, foi realizado biópsias de tecido hepático e tecido muscular para avaliar biomarcadores de ureogênese e metabolismo energético. Concentração sérica de progesterona (P4) foi avaliada no 36o dia pós-parto. Todas variáveis foram analisadas utilizando PROC MIXED do SAS 9.4 (SAS Inst., Cary, NC). A frequência de suplementação não alterou (P > 0.10) o PC, PC ajustado ao dia do parto (PCajus), PC após o parto (PCp), GMD, ECC, AOL e EGS no pré e pós parto. O PC (P = 0.079), PCajus (P = 0.078), e GMD (P = 0.074) foram maior para as vacas suplementadas no pré-parto. O ECC (P = 0.251), a AOL (P = 0.352), a EGS sobre o músculo longissimus (P = 0.199) e sobre o músculo Biceps femoris (P = 0.924) não foram afetados pela suplementação durante o pré-parto. Aos 105 dias após o parto, a suplementação não afetou (P > 0.10) o PC, GMD, ECC, AOL e EGS. O PC dos bezerros ao nascer, GMD e PC dos bezerros 105 dias após o parto não foram diferente (P > 0.10) de acordo com a suplementação e a frequência de suplementação. O consumo de matéria seca total e o consumo voluntário de forragem não foram afetados pela suplementação e frequência de suplementação durante o pré-parto (P > 0.10) e pós- parto (P > 0.10). Os animais suplementados diariamente apresentaram maiores níveis de glicose (P < 0.001) que os animais suplementados a cada três dias. Interação entre tratamento e tempo de coleta foi significativa para AA (P < 0.001), AA glicogênicos (P < 0.001), AA cetogênicos (P < 0.001), AA glico-cetogênicos (P < 0.001) e NUS (P = 0.005). A suplementação e frequência de suplementação não alteraram (P > 0.10) os níveis séricos de IGF-1, AGNE, -OH, colesterol e triglicerídeos. Do mesmo modo, a suplementação e frequência de suplementação não alteraram (P > 0.10) os níveis de proteína total, albumina e globulinas. A abundância da proteína carbamoil-fosfato sintetase-1 (CPS-1), os níveis de mRNA de carnitina palmitoyltransferase-1 (CPT-1) e do coativador-1α do receptor ativado por proliferador de peroxissoma (PGC-1α) não foram afetados (P > 0.10) pela suplementação e frequência de suplementação. Observou-se uma porcentagem semelhante (P = 0.606) de vacas com atividade ovariana (P4 > 1 ng/ml) e taxa de concepção (P = 0.842) entre os tratamentos. A suplementação proteica-energética durante o pré e pós-parto de vacas primíparas de corte em pastejo não melhora o desempenho e características metabólicas. Contudo, a redução da frequência de suplementação não resulta em efeitos negativos sobre o desempenho e características metabólicas.
The present study was performed to evaluate the effects of energy-protein supplementation and supplementation frequency during pre (105 d before calving) and postpartum (105 d after calving) of primiparous beef cows on performance and metabolic characteristics under grazing conditions. Twenty-four pregnant Nellore primiparous cows with average BW of 409±8.0 kg, 22±0.9 mo old and 172±2.5 d of gestation were used in this trial. Treatments were randomly assigned to primiparous cows: Control (ad libitum mineral mix), Daily Supplementation (1.5 kg/d of concentrate/animal) and Infrequent Supplementation (4.5 kg of concentrate/animal every three days). The BW, ADG, BCS, fat-thickness and ribeye area (RA) were evaluated at pre and postpartum period. Two 9-d intake-digestibility trials were performed throughout the experimental period where the first at 55 d before parturition, and the second at 55 d after parturition. Concentrations of glucose, IGF-1, NEFA, - OH, cholesterol and triglycerides were used as indicators of energy status, and free amino acids (AA), serum urea nitrogen (SUN), total protein, albumin and globulins were used as indicators of proteic status collected at 27 and 9 d before parturition, at the day of parturition, 9 and 27 d after parturition. Globulins were calculated subtracting the albumin quantified from the total protein level. Biopsies of hepatic and skeletal muscle tissues were performed at 27 d prior to calving to evaluate ureagenesis and energy metabolism biomarkers. Serum progesterone (P4) level was evaluated at the 36 th d postpartum. The response variables were analyzed using PROC MIXED of SAS 9.4 (SAS Inst., Cary, NC). The frequency of supplementation did not alter (P > 0.10) BW, adjusted BW at day of parturition (adjBW), BW after calving upon parturition (calvingBW), ADG, BCS, RA and fat-thickness during pre and postpartum. The BW (P = 0.079), adjBW (P = 0.078) and ADG (P = 0.074) were higher for supplemented cows during the prepartum. The BCS (P = 0.251), RA (P = 0.352), fat-thickness on longissimus muscle (P = 0.199) and on Biceps femoris muscle (P = 0.924) were not affect by supplementation during the prepartum. At 105 d after calving the supplementation did not affect (P > 0.10) BW, ADG, BCS, RA, and fat-thickness. Birth BW of calves, ADG and calf BW 105 d after calving were not different (P > 0.10) according to supplementation and frequency of supplementation. The total dry matter intake and forage voluntary intake were not affected by supplementation and supplementation frequency during prepartum (P > 0.10) and postpartum (P > 0.10). Daily supplemented animals had higher (P < 0.001) glucose levels than animals supplemented every three days. Interaction between treatment and sampling time was significant for AA (P < 0.001), glucogenic AA (P < 0.001), ketogenic AA (P < 0.001), gluco/ketogenic AA (P < 0.001), and SUN (P = 0.005). The supplementation and frequency of supplementation did not alter (P > 0.10) the levels of IGF-1, NEFA, -OH, cholesterol and triglycerides. Likewise, the supplementation and frequency of supplementation did not alter (P > 0.10) the levels of total protein, albumin and globulins. The protein abundance of carbamoyl phosphate synthase-1 (CPS-1), mRNA levels of carnitine palmitoyltransferase-1 (CPT-1) and peroxisome proliferator-activated receptor coactivator-1α (PGC-1α) were not affected (P > 0.10) by supplementation and supplementation frequency. Similar percentage (P = 0.606) of cows with ovarian activity (P4 > 1 ng/ml) and conception rate (P = 0.842) were observed among the treatments. The energy-protein supplementation during pre and postpartum of primiparous beef cows under grazing conditions do not improve performance and metabolic characteristics. However, the reduction of frequency of supplementation do not result negative effects on performance and metabolic characteristics.

Dissertação de Mestrado [Integrado] em Medicina Veterinária
In cattle production a good reproductive performance is essential to the herd's efficiency. In beef herds, the calf is the major product and so maximum reproductive efficiency is paramount in determining the herd's profitability. In a large number of cattle farms, reproduction is not optimal, which may have an important negative effect on the herd's economy. Therefore, the main goal of this work is to understand the influence of the caesarean section in the reproductive performance, specifically in the calving interval, breeding interval and culling rate, at different dam's ages and using different suture materials. After the retrospective analysis of 119 caesarean sections realized in a single farm, it was concluded that the number of caesarean sections and the use of Monodox® or Monosyn® for the uterus and Surgicryl® or Safil® for the peritoneum, muscles and skin, do not have a significant influence (p > 0.05) on the calving interval, breeding interval and culling rate. However, it should be emphasized that more data is needed to obtain results closer to reality and to allow for a better variables' evaluation. Furthermore, the study of other factors would be beneficial, since the parameters studied only explain a small part of the variation found.
RESUMO - O efeito do número de partos e diferentes fios de sutura no desempenho reprodutivo de vacas de carne submetidas a cesariana - Na produção de bovinos, um bom desempenho reprodutivo é essencial para a eficiência da exploração. No caso das vacadas de carne, o vitelo é o principal produto. Assim, a máxima eficiência reprodutiva é fundamental para a rentabilidade da exploração. Num elevado número de explorações de bovinos a reprodução não segue um plano ideal, limitando a sua própria economia. Assim, o objetivo deste trabalho foi compreender a influência da cesariana no desempenho reprodutivo das vacadas, avaliando o intervalo entre partos, o tempo de cobrição e a taxa de refugo em diferentes idades da fêmea e utilizando fios de sutura distintos. Após a análise retrospectiva de 119 cesarianas realizadas numa única exploração, concluiu-se que o número de cesarianas e a utilização de Monodox® ou Monosyn® para a sutura uterina e Surgicryl® ou Safil® para suturar o peritoneu, músculos e pele, não apresentaram uma influência significativa (p > 0.05) no intervalo entre partos, tempo de cobrição e taxa de refugo. No entanto, deve ser enfatizado que a continuação da recolha de dados permitiria não só a obtenção de resultados mais próximos da realidade, como uma melhor avaliação das variáveis. Adicionalmente, o estudo de outros fatores seria benéfico, já que os parâmetros agora estudados, apenas explicam uma pequena parte da variação encontrada.

Master of Science
Department of Animal Sciences and Industry
John Jaeger
Cattle grazing dormant native range (< 7% crude protein; CP) require supplementation of additional protein to sustain body weight (BW) and body condition score (BCS). Daily delivery of these supplements is an economic burden to cattle producers faced with challenging economic circumstances. Supplementing cows infrequently (as little as once/week) has produced equivalent BW and BCS changes compared to daily delivery. Dried distiller’s grains with solubles (DDGS) provides more ruminally-undegradable protein (RUP; 50-60%) compared to traditional oilseed-meal supplements (i.e. soybean meal) that are >50% ruminally-degradable protein (RDP). Therefore, our objective was to evaluate the effects of supplementation frequency on performance, reproductive success, eating behavior, and subsequent calf performance of spring-calving cows supplemented with DDGS. No differences in ending BW (P = 0.69) and BCS (P = 0.49), or changes in BW and BCS over the supplementation period (P = 0.82 and 0.70, respectively) were observed among cows supplemented every d, every 3 d, or every 6 d. Calf BW at birth, weaning weight (WW), and average daily gain (ADG) were similar among treatments (P = 0.19, 0.12, and 0.10, respectively). First-service conception rate (FSCR) and final pregnancy rate (PR) were also not affected by supplementation frequency (P = 0.62 and 0.76, respectively). The development of replacement heifers is a large expense for cow-calf producers. Improved breeding and heifer development strategies aimed at ensuring the success of replacement females have been developed but reproductive failure still remains a problem. The stress associated with breeding and handling procedures may decrease reproductive success. Therefore, the objective was to determine if intramuscular administration of flunixin meglumine (1.1 mg/kg BW) 14 days post-breeding would improve FSCR and PR in non-transported replacement heifers. Under the conditions of our study, flunixin meglumine did not improve (P = 0.87) first service conception rate above that of control heifers (41.2% and 42.3%, respectively). Final pregnancy rate also was not different between treatments and averaged 81.8% (P = 0.40).

The present investigation was designed to investigate the use of blessed thistle (Cnicus benedictus) in amelioration of fescue toxicosis in beef cattle. Twenty-seven crossbred Angus cows were blocked by age and weight into groups of three. Each group (n=9) was then randomly assigned to one of three dietary treatments: endophyte-free (EF), endophyte-infected (EI), or endophyte-infected with addition of cut and stemmed blessed thistle (EIBT). Each group was also randomly assigned to one of three 29-day replicates. Parameters measured during this trial included: urinary ergot alkaloid concentration (ng ergot alkaloids/mg creatinine), body weight (kg), rectal temperature (°C), serum progesterone (ng/ml), and serum prolactin (ng/ml). No effect of treatment (P>0.05) was detected in any of these parameters. A treatment x time interaction (P<0.0001) was observed for progesterone concentrations, likely a result of estrous cyclicity of cows. Results of this study suggest that we were unsuccessful in inducing fescue toxicity in test subjects assigned to EI and EIBT treatments. Minimal dietary ergovaline (1.72 μg kg-1) and cool ambient temperatures (-6.7°C to 23.3°C) likely contributed to this inability. Data from this research do suggest, however, that C. benedictus can be successfully incorporated into cattle diets. Further research will need to be performed to fully elucidate what, if any, benefits blessed thistle can have in the treatment of fescue toxicity.

Reproductive efficiency in beef cows is limited by the length of the postpartum anoestrous period which in turn is controlled by pituitary gonadotrophins and gonadal steroids and/or proteins. The first aim of this study was to elucidate the role of LH pulses in the development of ovarian activity in postpartum beef cows, specifically to determine whether or not the normal, relatively slow process of follicular development could be accelerated in cows in low body condition (BC) with pulses of gonadotrophin-releasing hormone (GnRH). The second aim was to determine the role of the metabolic hormones and in particular growth hormone (GH) in ovarian follicle development and function. Treatment of cows in low BC with pulsed intravenous infusions of 2μg every 2 hours from 5 to 7 weeks postpartum induced ovulation in 10 out of 12 cows. Saline infusions resulted in ovulation in only 1 of 12 cows in high BC and 1 of 11 cows in low BC groups. Plasma concentrations of GH, IGF-I and insulin were not affected by GnRH treatment, but cows in high BC had higher IGF-I and lower GH levels than cows in low BC. Gonadotrophin profiles, luteinizing hormone (LH) pulse frequency and LH pulse amplitude were not affected by either GnRH treatment or BC. Numbers of small (3-7.9 mm diameter) and large (≥ 8 mm diameter) follicles present at week 7 postpartum and numbers of LH receptors in theca and granulosa tissue were not affected by GnRH treatment or BC. The number of granulosa cells present in large follicles at week 7 postpartum was also unaffected. Intrafollicular concentrations of oestradiol, testosterone and IGF-I in large follicles at 7 weeks postpartum were not significantly affected by GnRH treatment or BC but there was a marked trend towards higher concentrations of oestradiol in cows in high BC compared with cows in low BC.

Concentrations of trace minerals within the body are known to impact reproductive processes. Thus, the current study analyzed the effects of using an injectable trace mineral supplement containing selenium, zinc, copper, and manganese during a superovulation protocol on embryo outcomes in donor beef cows and further effects on pregnancy rate in recipient females. We hypothesized that an injectable trace mineral (TM) supplement provided to cows fed to meet known nutrient requirements would increase TM status and influence superovulation, embryo characteristics, and enhance pregnancy rates. Our findings indicate that the injectable TM increased concentration of Se within the liver. However, superovulatory response, embryo production, quality grade, and developmental stage were not influenced by TM status. In addition, embryo treatment did not influence pregnancy rate, gestation length, or calf body weight.

Calves born to cows fed a protein supplement during late pregnancy have greater production characteristics compared to calves from cows not supplemented, despite similar birth weights. Our hypothesis was that cows receiving protein supplement during late gestation would have greater mammary gland blood flow allowing for enhanced lactation. Mammary gland hemodynamics were recorded during late gestation. While protein supplementation did not alter the blood flow to the mammary gland, this data demonstrates that mammary gland blood flow can be monitored during late pregnancy.

Two experiments were conducted at the University of Kentucky, Eden Shale Farm, Owenton, KY to evaluate the use of MTB-100TM (Alltech, Inc., Nicholasville, KY) to alleviate the symptoms of fescue toxicity when lactating Angus x Beefmaster cows and their calves grazed endophyte-infected KY-31 tall fescue. Experiment 1 provided a carbohydrate based toxin adsorbent, MTB-100TM, ad libitum in a commercial mineral supplement to project a daily consumption rate of 0, 20 or 40 g of MTB-100TM per cow. Cows were weighed, assigned a body condition score (BCS) and hair coat score (HC), rectal temperatures were recorded and fecal grab samples were taken for ergovaline (EV) and lysergic acid (LA) analysis every 35 days for three grazing seasons (May to September). Calves were also weighed and assigned a HC score. Although MTB-100TM did not improve cow or calf performance, cows older than 4 years and those with greater Beefmaster breeding exhibited a higher tolerance to fescue toxicity than 2 and 3-yr-olds and cows with greater Angus breeding. Experiment 2 was conducted to evaluate the response of lactating beef cows and their calves to strategic supplementation with MTB-100TM. MTB-100TM was mixed with a complete mineral so daily intake was projected to be 0 or 20 g/cow. The experimental period extended from May 5 to October 2 and was divided into 3 strategic periods: P1 = May 5 to July 5; P2 = July 5 to August 31; P3 = August 31 to October 2. Treatments were either 0 or 20 g•cow-1•d-1 MTB-100TM within a period (Treatment 1 = 0, 0, 0; Treatment 2 = 20, 0, 20; Treatment 3 = 0, 20, 0; Treatment 4 = 20, 20, 0; and Treatment 5 = 20, 20, 20). Cow and calf performance was measured the same as Exp. 1, but every 21 days. Supplementation early in the grazing season tended to improve cow weight gain and body condition; however, there was no effect on calf performance. Fecal output of EV and LA did not increase in either experiment with supplementation. In conclusion, strategically invoked MTB-100TM consumption can increase performance of cows grazing endophyte-infected tall fescue forage.