断奶应激对奶水牛犊牛血液生理生化指标和免疫功能的影响

为研究断奶应激对奶水牛犊牛的影响,选用5头健康犊牛,分别于断奶前1 d、断奶后1、14和21 d进行采血,测定犊牛的血常规、血清生化指标和免疫指标。结果显示,奶水牛犊牛的白细胞数、淋巴细胞数、红细胞数、单核细胞数、红细胞压积、天冬氨酸转氨酶活性、血糖含量、皮质醇含量、免疫球蛋白G含量在断奶前后无显著变化（P > 0.05）;中性粒细胞数在断奶后21 d显著低于断奶前1 d（P < 0.05）;血清乳酸脱氢酶、丙氨酸转氨酶活性在断奶后显著高于断奶前（P < 0.05）;血清尿素氮含量在断奶后21 d显著高于断奶前1 d（P < 0.05）;血红蛋白含量在断奶21 d显著低于断奶前1 d（P < 0.05）。结果表明断奶应激不仅影响了奶水牛犊牛的生理机能,而且降低了其免疫力和抵抗力。     

Effect of Weaning Stress on Blood Physiology and Biochemistry Indexes and Immune Function in Dairy Buffalo Calves

To study the effect of weaning stress on dairy buffalo calves,5 healthy calves were chosen and weaned,and the blood samples were collected at 1 day before weaning,and 1,14 and 21 days after weaning to analysis blood physiology and biochemistry indexes and immune function.The results showed that the count of white blood cell,lymphocyte,erythrocyte,monocytes and hematocrit,aspartate aminotransferase activity,blood glucose,cortisol and immunoglobulin G contents of dairy buffalo calves were no significant difference between before and after weaning treatments (P > 0.05).The count of neutrophils at 21 d after weaning were significantly lower than that of 1 d before weaning of dairy buffalo calves (P < 0.05).However,lactate dehydrogenase and alanine aminotransferase activity in weaned treatments were significantly higher than those of animals in the treatment before weaning (P < 0.05).The serum urea nitrogen of dairy buffalo calves at 21 d after weaning was significantly higher than that of 1 d before weaning (P < 0.05) and hemoglobin content at 21 d after weaning was significantly lower than that at 1 day before weaning (P < 0.05).It indicated that the physiological and immunity function of dairy buffalo calves were challenged under weaning stress.     

Prevalence and importance of endoparasites in calves raised in Swiss cow-calf farms]

A longitudinal study was performed to establish estimates of prevalence of selected endoparasites in Swiss cow-calf operations and to investigate the importance of an infection with endoparasites on diarrhea and weight gain until weaning. Three hundred and eighty-six calves raised in 67 larger cow-calf herds were included in the study. Faecal samples were collected during the first three months of life and at weaning. Parasitological analyses were performed according to standard procedures including specifically the detection of Eimeria spp., Cryptosporidium parvum, Strongyloides papillosus and Trichostrongylida. The effects of an infection with endoparasites on weight gain were analyzed with a linear model accounting for effects of farm, breed, sex, calving month and weight at birth. The average prevalences of endoparasites within the first three months of life were: E. bovis 36%, E. zuernii, 19%, C. parvum 16.8%, S. papillosus 22.3% and Trichostrogylida 1.5%. The prevalence of diarrhea within the same time period was 13%. Prevalences at weaning (at the end of the grazing period) were: E. bovis 56.5%, E. zuernii 4.6%, C. parvum 3.7%, S. papillosus 14.4% and Trichostrogylida 84.5%. With the exception of E. zuernii, endoparasites were more frequently observed in healthy calves than in diarrheic calves. Weaning weights were available from 190 calves (33 herds). Statistical analyses of weaning weights revealed no evidence that an infection with helminths and/or protozoa within the first three months of life or at weaning had a negative influence on individual weight gain.     

Combined administration of ghrelin and GHRH synergistically stimulates GH release in Holstein preweaning calves

Ghrelin is a gut peptide which participates in growth regulation through its somatotropic, lipogenic and orexigenic effects. Synergism of ghrelin and growth hormone-releasing hormone (GHRH) on growth hormone (GH) secretion has been reported in humans and rats, but not in domestic animals in vivo. In this study, effects of a combination of ghrelin and GHRH on plasma GH and other metabolic parameters, and changes in plasma active and total ghrelin levels were studied in Holstein bull calves before and after weaning. Six calves were intravenously injected with vehicle (0.1% BSA-saline), ghrelin (1 microg/kg BW), GHRH (0.25 microg/kg BW) or a combination of ghrelin plus GHRH at the age of 5 weeks and 10 weeks (weaning at 6 weeks of age). Ghrelin stimulated GH release with similar potency as GHRH and their combined administration synergistically stimulated GH release in preweaning calves. After weaning, GH responses to ghrelin and GHRH became greater compared with the values of preweaning calves, but a synergistic effect of ghrelin and GHRH was not observed. The GH areas under the concentration curves for 2h post-injection were greater in weaned than in preweaning calves (P<0.05) if ghrelin or GHRH were injected alone, but were similar if ghrelin and GHRH were injected together. Basal plasma active and total ghrelin levels did not change around weaning, but transiently increased after ghrelin injection. Basal plasma insulin, glucose and non-esterified fatty acid levels were reduced after weaning, but no changes by treatments were observed. In conclusion, ghrelin and GHRH synergistically stimulated GH release in preweaning calves, but this effect was lost after weaning.     

日粮氨基酸对犊牛生长和健康影响的研究进展

犊牛在断奶前免疫系统发育不成熟，体质敏感，而在断奶后生长发育迅速。这两个阶段的犊牛都需要提供含有优质蛋白质的日粮以保证其生长发育。结合中国蛋白质资源紧缺的现状，做好犊牛阶段的氨基酸营养在促进犊牛健康生长和提高蛋白质利用率上都具有重要作用。此外，氨基酸在提高犊牛免疫力方面有不可替代的作用，近年来的研究还发现，氨基酸对犊牛消化道易感细菌和病毒有特殊的抑制功能。针对犊牛生长速度快、免疫功能不完善、死亡率高、断奶前后生理结构和营养需要变化迅速的生理特点，作者重点介绍了单一氨基酸不同水平及多种氨基酸不同比例对犊牛断奶前后生长性能的影响，并从氨基酸提高犊牛自身免疫力和抑制微生物繁殖两方面来阐述氨基酸对犊牛健康的影响机制，以期为推进氨基酸在犊牛生产中的应用提供理论依据。     

犊牛早期(3月龄)断奶生长发育情况分析

[目的]探索犊牛早期(3月龄)断奶的可行性,为推广犊牛早期(3月龄)断奶技术提供依据,增加养殖企业的经济效益成本。[方法]试验选取出生后3月龄的西门塔尔犊牛,进行断奶饲养,测量断奶后不同日龄的体重及体尺指标,分析其生长发育情况,并对体重及体尺进行相关性分析。[结果]西门塔尔犊牛断奶后增重快速,断奶后90天,犊牛平均体重达到269.67kg,断奶后平均总增重达到101.54kg,全程日均增重为1128.22g。断奶后90天与断奶后30天比较,体斜长、体高、胸宽、胸深、胸围、腹围、臀围均呈现增加的趋势,其中增长较快的是腹围,其次是胸围,分别增加了19.0cm,14.67cm。体重与体斜长、体高、胸宽、胸深、胸围、腹围、臀围均呈正相关,其中体重与体斜长、体高、胸深、胸围、腹围呈极显著相关(p<0.01)。[结论]犊牛早期(3月龄)断奶后犊牛生长发育情况较好,犊牛早期(3月龄)断奶具有较强的可行性,可大范围推广。     

Influence of calving season and stocking rate on birth weight and weaning weight of Simmental-sired calves from Brahman-Hereford F1 dams.

Braham-Hereford F1 dams have been used to evaluate the influence of grazing pressure on forage attributes and animal performance at the Texas A&M University Agricultural Research Center at Overton. Data for this study were compiled from 1,909 records of Simmental-sired calves born to Braham-Hereford F1 cows from 1975 to 1990. Birth weight and weaning weight were analyzed independently to estimate the influence of year, season of birth, dam age, weaning age, and sex of calf. The effect of stocking rate as represented by levels of forage availability on weaning weights and subsequent birth weights was measured. Within the fall and winter calving seasons, lactating dams grazing at a high stocking rate produced calves with the lowest subsequent birth weights. Lactating dams assigned to creep-fed treatments had calves with the heaviest subsequent birth weights. Although dams that were less than 3.5 yr of age had calves with the lightest birth weights, there was no apparent decline in birth weight of calves from dams 12 to 17 yr old. Year, sex of calf, age of dam, stocking rate, season of birth, age at weaning, and birth weight were significant factors affecting weaning weight (P less than .01). Fall-born calves grazing cool-season annual pastures were heavier at weaning (267.6 kg) than either winter- (252.0 kg) or spring-born calves (240.9 kg). A stocking rate x season-of-birth interaction was observed for birth weight and weaning weight (P less than .05). Differences in weaning weight from low- vs high-stocked pastures were greater for fall-born calves (61.6 kg) than for winter-born calves (48.7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Performance of free suckling dairy calves in an automatic milking system and their behaviour at weaning

Abstract

The performance of dairy calves allowed to suckle freely (FS) until eight weeks of age in a cubicle system with automatic milking was compared to automatic teat-feeding with low milk (LM) or high milk (HM) substitute allowances. Weight gain and feed intake of FS (n = 13), LM (n = 23) and HM (n = 22) calves were recorded until two weeks after abrupt weaning, and their behaviour was studied during weaning. FS calves had higher weight gain, but much lower solid feed intake until weaning, than LM and HM calves and their advantage in weight remained throughout the study despite very low post-weaning gain. During the first 24 hours after weaning, FS calves displayed more behavioural signs of stress. However, at 72 hours after weaning, behaviour was similar for all treatments. Methods to stimulate solid feed intake before weaning need to be developed to draw advantage of the FS system.     

Stress significantly increases mortality following a secondary bacterial respiratory infection

ABSTRACT: A variety of mechanisms contribute to the viral-bacterial synergy which results in fatal secondary bacterial respiratory infections. Epidemiological investigations have implicated physical and psychological stressors as factors contributing to the incidence and severity of respiratory infections and psychological stress alters host responses to experimental viral respiratory infections. The effect of stress on secondary bacterial respiratory infections has not, however, been investigated. A natural model of secondary bacterial respiratory infection in naive calves was used to determine if weaning and maternal separation (WMS) significantly altered mortality when compared to calves pre-adapted (PA) to this psychological stressor. Following weaning, calves were challenged with Mannheimia haemolytica four days after a primary bovine herpesvirus-1 (BHV-1) respiratory infection. Mortality doubled in WMS calves when compared to calves pre-adapted to weaning for two weeks prior to the viral respiratory infection. Similar results were observed in two independent experiments and fatal viral-bacterial synergy did not extend beyond the time of viral shedding. Virus shedding did not differ significantly between treatment groups but innate immune responses during viral infection, including IFN-γ secretion, the acute-phase inflammatory response, CD14 expression, and LPS-induced TNFα production, were significantly greater in WMS versus PA calves. These observations demonstrate that weaning and maternal separation at the time of a primary BHV-1 respiratory infection increased innate immune responses that correlated significantly with mortality following a secondary bacterial respiratory infection.     

Effects of oral vitamin E supplementation during late gestation in beef cattle that calved in late winter and late summer

OBJECTIVE: To determine effects of breed and oral vitamin E supplementation during late gestation on serum vitamin E and IgG concentrations in beef cows that calved in late winter and late summer and in neonatal calves. ANIMALS: 73 Angus and 43 Hereford primiparous and multiparous cows and their calves. PROCEDURE: Cows in groups that were homogeneous regarding breed and age distribution were randomly allotted to groups that were orally supplemented (n = 59) or not supplemented (57) with vitamin E beginning 30 days prior to onset of 65-day calving seasons. Supplemental vitamin E was provided in a vitamin-mineral mix offered free-choice until parturition. RESULTS: Cows that calved in late winter and were supplemented orally with vitamin E had higher serum vitamin E concentrations at calving and after calving than did unsupplemented cows; differences between groups before calving were not significant. Calves from supplemented multiparous cows had higher vitamin E concentrations than did calves from unsupplemented cows. Winter-born calves from supplemented Hereford cows had heavier 205-day adjusted weaning weights than did winter-born calves from unsupplemented Hereford cows. Supplementation did not affect vitamin E or IgG concentrations in the herd that calved in late summer and did not affect calf growth. CONCLUSIONS AND CLINICAL RELEVANCE: Oral vitamin E supplementation during late gestation may be economically beneficial in certain cow-calf operations in which late-gestation cows are consuming stored forages.     

Weaning and post-weaning performance by fall-born beef calves weaned on different dates in the spring from Neotyphodium coenophialum-infected tall fescue pastures

Fall-born calves grazing Neotyphodium coenophialum-infected tall fescue [E+; Lolium arundinaceum (Schreb.) Darbysh.] pastures should benefit from early weaning because of reduced exposure to fungal toxins. However, fall-born calves that grazed E+ and were weaned in mid-April had reduced post-weaning performance compared with calves managed similarly but weaned in early June. Gelbvieh × Angus calves (n = 238) were used in a 3-year study to determine the optimal time to wean fall-born calves grazing E+. Cow/calf pairs were allocated randomly to one of four weaning date treatments: 1) March 16 (177 ± 4.7 days of age; MarW), 2) April 13 (204 ± 4.7 days of age; AprW), 3) May 11 (236 ± 4.7 days of age; MayW), and 4) June 8 (264 ± 4.8 days of age; JuneW). On their assigned weaning date, calves were weighed, vaccinated, blood samples were collected, and calves were moved to 3.2-ha pastures adjacent to their dams for 14 days. After the weaning period, calves were weighed, blood samples were collected, and then calves were moved to pastures containing non-toxic forages. Birth weight and calf weights on MarW, AprW, and MayW weaning dates did not differ (P ≥ 0.21) across weaning date treatments. However, calf weaning weights on their respective weaning dates, weight on JuneW and on June 22 (14 days following the JuneW), daily gain between birth and June 22, and weight change between MarW and JuneW increased linearly (P < 0.05) across weaning dates. Linear decreases (P < 0.05) across weaning dates were noted for antibody titers to bovine virus diarrhea (BVD) and infectious bovine rhinotracheitis (IBR), serum Cu, and platelets at the time of actual weaning. Linear increases (P < 0.05) across weaning dates were noted for: i) total antioxidant potential and eosinophils at weaning; ii) changes in antibody titers to BVD and IBR, total antioxidant potential, and serum Zn during the 14-day post-weaning period; and iii) and changes in BVD and BRSV titers and serum Cu between actual weaning date and June 22. Heifer weight at breeding increased (P < 0.05) and steer weight at shipping, hot carcass weight and backfat thickness tended (P ≤ 0.10) to increase linearly across weaning dates. Final feedlot weight and gain did not differ (P ≥ 0.18) among weaning dates. Therefore, delaying weaning of fall-born calves grazing E+ pastures until early June may be beneficial for calf weight and immune function at weaning, and heifer weight at breeding, but those benefits in steers may be mitigated through the feedlot period.     

Effects of sex and age on behavior and weight gain in beef calves after abrupt weaning

The effects of weaning on beef calves of different ages were investigated. Forty male and 40 female calves were either weaned at 6 (W6, n = 40) or 8 (W8, n = 40) months of age. The vocalization activity and behaviors (feeding, lying and standing/walking) were observed during the first 3 days following weaning. Body weight was recorded at 6 and 8 months and 2 weeks following weaning. W6 animals vocalized more often than W8 calves and females more than males on day 1 (P < 0.05). The vocalization activity decreased at a higher rate in W8 than in W6 from days 1 to 3. On day 2, W6 calves spent less time lying and more standing/walking than W8 calves (P < 0.05). The behaviors did not differ between males and females. The average daily gain after weaning did not differ between weaning ages (P > 0.05), but W8 calves gained more from 6 to 8 months of age. In conclusion, weaning distress was more pronounced in W6 than in W8 calves. W8 calves also had a superior growth performance during 6 to 8 months of age. The effect of the calves' sex was less pronounced. Therefore, it is recommended to wean beef calves later than 6 months of age.     

Concentration of plasma cholesterol in beef cows and calves, milk production and calf gain.

Milk yield of 59 beef cows that calved in late September through November was measured monthly in early and late lactation and biweekly during midlactation. Milk yield was estimated by milking with a machine after over-night separation of cows from calves. Concentration of plasma cholesterol of cows and calves was measured when calves averaged 44, 93, 136, and 178 d of age (SD = 17 d). Cholesterol of calves also was measured 2 wk after weaning, when they averaged 220 +/- 2.3 d of age. Cholesterol of calves was highest at second and third samplings and dropped after weaning. The estimated intake of milkfat by calves, and to a lesser extent their intake of milk, was related positively to their plasma cholesterol as they approached weaning age. The relationship was not strong enough, however, for differences among calves in concentration of plasma cholesterol to identify accurately differences in milk yield of their dams. Within breed group, age of cow, and stage of lactation, the regression coefficients of milk yield on plasma cholesterol of cows were close to zero. The concentrations of plasma cholesterol in both cows and calves were highly repeatable, with the exception of samples that were collected when calves averaged 44 d of age. Although plasma cholesterol of calves was related positively to milk yield and milkfat yield in late lactation, the former trait was not an accurate indicator of the two latter traits.     

A spline polynomial model to describe serum IGF-I concentration from birth to slaughter in calves: effects of weaning age,pre-weaning concentrate feeding and breed

The statistical analysis of hormones sampled throughout the production cycle is complicated because factors such as age and weight at the measuring date interfere. Spline curves constructed from pieces of low-degree, random-effects polynomials could be used for a more accurate analysis of data. Concentration of insulin-like growth factor-1 (IGF-1), weight gain, and concentrate intake of Parda de Montaña (PM) (n = 27) and Pirenaica calves (n = 14) were modeled with a spline model according to age at weaning, pre-weaning concentrate feeding, and breed. At birth, calves were randomly assigned to early weaning (EW) at 90 d or traditional weaning (TW) at 150 d. During lactation, half of PM calves received concentrates (S), whereas the remainder received no concentrates (NS). After weaning, calves received concentrates on an ad libitum basis until they reached a weight of 450 kg. The spline model had better likelihood than a polynomial of 6 degrees or a split-plot model. Serum IGF-1 concentration was greatly affected by age at weaning and pre-weaning concentrate feeding, but not by breed. In NS calves, IGF-1 concentration was greater in EW than in TW calves from 120 to 300 d, irrespective of breed. During lactation, S calves had greater IGF-1 concentration than NS calves. After weaning, EWNS calves reached the IGF-1 concentration of EWS calves after 4 mo on concentrates, whereas TWNS calves attained IGF-1 concentration of TWS calves after only 2 mo, because of their increased concentrate intake relative to TWS calves. Concentration of IGF-1 was positively correlated with the immediate weight gains and intake, but it was not a good predictor of performance in the long term.     

The calf training for loading onto vehicle at weaning

The aim of this study is to examine whether calf training for loading at the weaning period improves later loading. Five calves were allocated to the trained group and the control group, respectively. Calves in the trained group were loaded onto a livestock trailer for 5 successive days at weaning. Trainers led or hauled the calves by rope only. When loading was completed, trainers fed calves with sugar cubes as rewards. Calves in the control group were weaned without any treatment. Five weeks after weaning, tests were carried out under similar conditions as the trained group. Loading efficiency, physical effort on the handler and handling stress on calves between groups were compared. Trained calves were loaded significantly faster than control calves. Trained calves balked less during loading than control calves. Heart rates of handlers after loading were significantly lower in the trained group than in the control group; however, salivary amylase activity and cortisol concentration was not different between groups. Physical effort and stress on handlers would be almost the same in both groups. Heart rate, plasma cortisol, NEFA and CPK of calves were significantly increased only in the control group after loading. These results show calf training improves loading efficiency and reduces stress on calves.     

Heterosis retention for birth and weaning characters of calves in the third generation of a five-breed diallel.

Data were 876 birth records and 727 weaning records of straightbred and F3 crossbred calves produced in the third generation of a five-breed diallel. Among straightbreds at birth, Holstein calves were heaviest and widest at the shoulders and hips. Jersey calves were lightest and narrowest at the hips, and Brahman calves were narrowest at the shoulders. Holstein crosses tended to be larger at birth than crosses among other breeds. Among straightbreds at weaning, Holstein calves were heaviest and tallest, and Hereford calves were lightest and shortest. Angus calves had the highest survival to weaning rate, and Holstein calves had the lowest survival rate. Among crossbred calves, Holstein crosses tended to be larger at weaning. Estimates of average heterosis retained for birth characters were not significant. Significant breed mean heterosis retention was observed for birth weight, shoulder width, and hip width of Hereford calves and for shoulder width and hip width of Holstein calves. Estimates of average heterosis retained for weaning weight and height were 6.1 kg (P less than .01) and 1.02 cm (P less than .05), respectively. In general, estimates of specific and average heterosis retained for survival to weaning were nonsignificant. Significant breed mean heterosis was observed for weaning weight and height of Brahman, Hereford, and Holstein calves and for survival to weaning of Hereford, Holstein, and Jersey calves.     

Factors associated with intersucking in Swiss dairy heifers

Intersucking is a problem that may lead to udder damage, mastitis, milk loss, and culling of breeding animals. To analyse the risk factors for intersucking in dairy heifers in Switzerland, we asked 130 randomly selected dairy farmers about a broad spectrum of environmental factors that might be associated with intersucking (such as housing conditions, management, and the feeding of calves and heifers). In total, 2768 heifers (Swiss Brown Cattle, Simmental and Holstein Friesian) were included of which 303 had ever performed intersucking. Data at the farm level were analysed using path analysis (linear and logistic regression). Two outcome variables were considered: the occurrence of intersucking on the farm and the proportion of intersucking heifers above the cut-off of 7.2%. Farms where calves had no access to barnyard or pasture, where calves were reared in pens in enclosed buildings, where heifers after weaning were not restrained while feeding, where heifers after weaning received <0.5 kg concentrate per day, and where heifers after weaning were fed ≥40% maize silage (dry-matter ratio) were most likely to have intersucking heifers.     

Productivity of cow-calf pairs grazing tall fescue pastures infected with either the wild-type endophyte or a nonergot alkaloid-producing endophyte strain, AR542

The nonergot alkaloid-producing endo-phyte, AR542, has been shown to improve the persistence and yield of tall fescue pastures without causing the animal disorders commonly associated with tall fescue toxicosis. A 3-yr grazing study was conducted to compare effects of AR542-infected tall fescue pastures with wild type endophyte-infected (E+) tall fescue pastures on cow-calf performance. Replicated 7.3-ha pastures of each treatment were grazed by cow-calf pairs (16 pairs per pasture replication) each year from March to weaning in September. The cows were exposed to breeding on their respective pasture treatments from April 1 through June 15. The treatment groups were compared for reproductive performance, ADG, BCS, calf growth rate, and weaning weight. Blood samples were also collected for serum prolactin (PRL) analysis. There were no significant differences in calving rate (P = 0.98) or calving interval (P = 0.62) between pasture treatments. Cows that grazed the AR542 pastures subsequently gave birth to calves that were heavier (P < 0.05) than calves from cows that had grazed the E+ pastures. Cows grazing the AR542 pastures had higher (P < 0.05) BCS at the end of the grazing period, and had higher ADG during the grazing period. Calves raised on the AR542 pasture had higher (P < 0.05) ADG and weaning weights than calves of the same sex raised on the E+ pastures. Serum PRL concentrations were decreased (P < 0.05) in both cows and calves on the E+ pastures compared with serum PRL concentrations in cows and calves grazing the AR542 pastures. The results indicate that grazing tall fescue pastures infected with the AR542 endophyte may give significant advantages in cow-calf growth rates and BCS over grazing E+ pastures. However, there did not seem to be any benefit in reproductive performance in this trial. There was a small, but significant increase in birth weight in cows grazing AR542 pasture.     

Nursing enhances the negative effect of estrogen on LH release in the cow

Twenty-three crossbred beef cows between 4 and 5 yr of age were assigned at random to one of six treatments: (1) ovariectomized 4 d postpartum (OVX) with early weaning of calves 21 d postpartum (OVX-EW; n = 4), (2) OVX-EW and 17 beta-estradiol implants (OVX-E2-EW; n = 4), (3) OVX and normal nursing by calves throughout the experiment (OVX-NN; n = 3), (4) OVX-NN and 17 beta-estradiol implants (OVX-E2-NN; n = 4), (5) intact cows and early weaning of calves 21 d postpartum (EW), (6) intact cows and normal nursed (NN). Blood was collected at 15-min intervals over a 4-h period once weekly during the 12-wk postpartum period in the OVX cows. Early weaned intact cows exhibited estrus 23 d sooner (P less than .05) than normally nursed cows. A hormone level for each cow at each week was determined from the mean of the 17 samples collected over the 4 h period each week. There were no significant changes due to E2 treatment, for concentrations of LH, FSH or number of pulses during wk 1 through 3. However, during wk 4 through 12 the linear and quadratic contrasts of wk X estrogen X nursing were significant for serum LH, indicating there was no difference between the treatments for EW and NN without E2 but there was a large difference in the presence of E2. During nursing E2 suppressed serum LH below that of nonestrogen-treated cows while after weaning E2 stimulated LH release above that of nonestrogen-treated cows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Postweaning performance of calves from Angus, Brahman, and reciprocal-cross cows grazing endophyte-infected tall fescue or common bermudagrass

Data from 403 Polled Hereford-sired calves from Angus, Brahman, and reciprocal-cross cows were used to evaluate the effects of preweaning forage environment on postweaning performance. Calves were spring-born in 1991 to 1994 and managed on either endophyte-infected tall fescue (E+) or common bermudagrass (BG) during the preweaning phase. After weaning, calves were shipped to the Grazinglands Research Laboratory, El Reno, OK and stratified to one of two winter stocker treatments by breed and preweaning forage; stocker treatments were winter wheat pasture (WW) or native range plus supplemental CP (NR). Each stocker treatment was terminated in March, calves grazed cool-season grasses, and calves were then moved to a feedlot phase in June. In the feedlot phase, calves were fed to approximately 10 mm fat over the 12th rib and averaged approximately 115 d on feed. When finished, calves were weighed and shipped to Amarillo, TX for slaughter. Averaged over calf breed group, calves from E+ gained faster during the stocker phase (P<.10), had lighter starting and finished weights on feed (P< .01), lighter carcass weights (P<.01), and smaller longissimus muscle areas (P<.05) than calves from BG. Calves from E+ were similar to calves from BG in feedlot ADG, percentage kidney, heart, and pelvic fat, fat thickness over 12th rib, yield grade, marbling score, and dressing percentage. Maternal heterosis was larger in calves from E+ for starting weight on feed (P<.01), finished weight (P<.10), and carcass weight (P<.16). These data suggest that few carryover effects from tall fescue preweaning environments exist, other than lighter, but acceptable, weights through slaughter. These data further suggest that the tolerance to E+ in calves from reciprocal-cross cows, expressed in weaning weights, moderated postweaning weight differences between E+ and BG compared to similar comparisons in calves from purebred cows.