Fertility in perimenopausal women

This study evaluated the effects of recombinant bovine somatotropin (bST; one injection of 320 mg per ewe) on milk production and composition and on the grazing behavior of multiparous ewes in the third to fourth lactation. Forty Comisana lactating ewes were divided into four groups: 1) untreated, grazing on natural pasture (botanical composition: 35% of Graminaceae, 49% of Fabaceae, 6% of Cruciferae, 10% of other families) at a low stocking rate (16 m2/d); 2) untreated, grazing at a high stocking rate (8 m2/d); 3) treated with bST, grazing at a low stocking rate; and 4) treated with bST, grazing at a high stocking rate. The diets of the ewes were supplemented with vetch and oat hay (500 g/d) and with concentrate (500 g/d). Treatment increased milk production (923.8 vs. 669.5 g/d) but had little effect on fat and protein contents. Administration of bST significantly increased herbage intake; the effect on intake was more marked at the high stocking rate. Under these grazing conditions, the treated ewes reduced selective intake behavior and, thus, achieved good feed intake despite the low biomass availability.     

Growth, reproductive performance, mammary development, and milk production of beef heifers as influenced by prepubertal dietary energy and administration of bovine somatotropin

Three trials with 156 crossbred heifers were used to determine the effects of dietary energy and bovine somatotropin administration on subsequent heifer productivity. In Trial 1, heifer calves were weaned from their dams (n = 28; 113 +/- 13 d of age) and assigned to a 2 x 2 factorial arrangement of moderate (MDE) or high dietary energy (HDE) and injections of vehicle (VEH) or 250 mg of bovine somatotropin (bST) every 14 d. Heifer calves in Trial 2 (n = 28; 123 +/- 20 d of age) and Trial 3 (n = 100; 134 +/- 22 d of age) nursed their dams while grazing pasture and received no creep feed (MDE) or ad libitum access to creep feed (HDE) and received VEH or bST as in Trial 1. Treatments were administered for 112 d and heifers within trial were managed alike after that time. There were no dietary treatment x bST treatment interactions for any of the variables analyzed (P > .05). Dietary energy did not affect daily gain in Trial 1; however, heifers receiving HDE in Trials 2 and 3 had greater weight, hip height growth, and fat thickness (P < .01) by the end of the treatment period. Treatment with bST increased gain in Trials 1 and 2 (P < .01) but did not affect growth in Trial 3. There were trends in all trials for HDE to reduce age at puberty (P < .15), but there were no consistent effects of bST on reproductive measures. Mammary gland composition and milk production were unaffected by treatment in Trial 1. In Trial 2, HDE decreased subsequent milk production, calf weaning weight, and mammary dry fat free tissue and DNA (P < .05). Treatment with bST in Trial 3 tended (P = .08) to result in greater milk production and increased calf weaning weights (P < .05). We conclude that bST treatment may enhance growth with no effect on reproduction. Treatment with bST did not overcome deleterious effects of HDE on milk production but may play an important role in mammogenesis.     

Effects on nutrient and hormonal profile of long-term infusions of glucose or insulin plus glucose in cows treated with recombinant bovine somatotropin before peak milk yield

Ten Holstein cows were treated with 30.9 mg.d-1 of recombinant bST from 15 to 41 d of lactation. The Latin square design included three infusion periods of 6 d each with 3 d of rest between infusion periods. Infusions were physiological saline, glucose (50 g.h-1), and insulin plus glucose (12.5 IU.h-1 + 50 g.h-1). Blood was collected continuously during the last 24 h of each infusion period. Statistical analyses of data for energy balance, milk yield, and DMI were performed on the last 3 d of each infusion period. Production data before and after infusions (i.e., no recombinant bST) estimated that recombinant bST increased milk yield of cows infused with glucose and saline by 3.1 and 3.6 kg.d-1, respectively. Net energy intake was not affected by infusion, but glucose infusion resulted in higher BW loss than did saline infusion (2.33 vs. 0.08 kg.d-1, respectively), and insulin plus glucose infusion resulted in BW gain (0.65 kg.d-1). Milk yield was 39.9, 39.6, and 37.6 kg.d-1 for cows infused with saline, glucose, and insulin plus glucose, respectively. The insulin plus glucose infusion increased milk protein 11 and 14% compared with response to saline and glucose infusions, respectively; no change occurred in the proportion of casein and whey proteins. Serum bST was increased 109% with exogenous recombinant bST. Serum IGF-I was lower for cows infused with glucose than for those infused with saline (21.03 vs. 27.44 ng.ml-1) and increased to 46.55 ng.ml-1 for cows infused with insulin plus glucose. Serum concentrations of insulin and glucose were 13.7 and 56.7, 18.5 and 61.9, and 30.5 muIU.ml-1 and 39.4 mg.dl-1 for cows infused with saline, glucose, and insulin plus glucose, respectively. The results of this study suggest that low concentrations of plasma insulin in early lactation may limit the IGF-I response to recombinant bST (uncoupling). Despite higher IGF-I, milk yield was lower, probably as a result of low blood glucose. These results suggest that, in early lactation, insulin is still anabolic because the BW gain of cows increased. However, milk yield was still higher than that for cows in late lactation with similar insulin concentrations.     

Responses of dairy cows supplemented with somatotropin during weeks 5 through 43 of lactation

Beginning at wk 5 of lactation, 136 cows (34 per treatment) were supplemented daily for 38 wk with 0, 10.3, 20.6, or 41.2 mg of recombinantly derived bST monomer. Cows were obtained from University of Kentucky, University of Minnesota, University of Pennsylvania, and The Ohio State University. Nine cows (4 at 0 mg/d, 1 at 10.3 mg/d, 1 at 20.6 mg/d, and 3 at 41.2 mg/d) did not complete the experiment because of health problems. Data from these cows were included in the reproduction and health databases but not in the production database. Cows supplemented with bST produced more milk, consumed more feed, had lower rates of BW gain, and had improved efficiencies of milk production (conversion of feed and NEL to milk). Additional increases in productivity were modest at 20.6 and 41.2 mg/d versus productivity at 10.3 mg/d of bST. Concentrations of fat, protein, and TS in milk were unaffected. At 10.3 mg/d, bST did not adversely affect reproduction or health.     

Response of Brazilian crossbred cows to varying doses of bovine somatotropin

The effect of n-methionyl bovine somatotropin (bST) on milk yield was evaluated in crossbred cows (40 1/2 Bos indicus x 1/2 Bos taurus and 18 1/4 B. indicus x 3/4 B. taurus) in Brazil. Cows were randomly assigned to treatments within stage of lactation [stage 1 = 56 to 100 d in milk (DIM); stage 2 = 101 to 199 DIM] and breed groups (1/2 vs. 1/4 B. indicus blood). Treatments were 250 or 500 mg of bST administered every 14 d. Cows in the control group did not receive bST or a placebo. Treated cows received bST injected subcutaneously in the postscapular region, alternating between the left and right sides. The 26-wk experiment consisted of 2 wk of pretreatment and 24 wk of treatment. Cows were housed in an open lot with regulated access to pasture. Cows were milked twice daily and scored for body condition at 2-wk intervals. Compared with controls, milk yield increased equally (22%) for cows receiving 250 or 500 mg of bST. Milk yield response to bST was higher and persisted longer during stage 1 of lactation than during stage 2 of lactation. No difference in response to bST was noted between cows with 1/2 or 1/4 B. indicus blood. Cows treated with 500 mg of bST tended to have more mastitis, but no other adverse health effects were observed. The potential use of 250-mg doses of bST at 14-d intervals in crossbred cattle in Brazil and other subtropical regions throughout the world is suggested, particularly before about 220 DIM.     

Administration of recombinant bovine somatotropin to dairy cows for four consecutive lactations

Effects of long-term administration of recombinant bovine somatotropin (bST) to dairy cows on complete lactational performance [60 (+/- 3) to 284 (+/- 3) d in milk (DIM)] were studied for four consecutive lactations. Beginning on d 60 (+/- 3) postpartum, Holstein cows received biweekly injections (500 mg) of bST (n = 39) or a placebo (control; n = 39) during the first lactation of the study. Cows either continued on the same treatment (n = 26) or were switched to the opposite treatment (n = 29) during the second lactation. Cows that changed treatments were injected for only 16 wk during the second lactation. Six cows per treatment completed four consecutive lactations. Treatment with bST during the first lactation did not have a residual effect on milk yields during the second lactation. Injections of bST during the second lactation increased milk yield 6.5 kg/d from 60 (+/- 3) to 172 DIM. For the four lactations, cows receiving bST yielded 3.7 kg/d (14%) more milk and gained 52 kg (37%) more body weight than did controls. Pretreatment (from 0 to 56 DIM) milk yields in yr 2, 3, and 4 were not affected by previous bST treatment. Milk yield, efficiency of feed utilization, and body weights were enhanced in cows injected with bST for four consecutive lactations. Previous bST treatment did not diminish milk yields in subsequent lactations.     

Production and composition of milk from Jersey cows administered bovine somatotropin and fed ruminally protected amino acids

Eight multiparous and 4 primiparous Jersey cows averaging 92 d of lactation were utilized in a replicated 4 x 4 Latin square design with 28-d periods to determine responses to bovine somatotropin (bST) and ruminally protected Met and Lys when diets were fed that contained supplemental fat. Treatments were 1) control [no bST or ruminally protected amino acids (AA)], 2) control plus bST, 3) control plus ruminally protected AA, and 4) control plus bST plus ruminally protected AA. Dry matter intake was increased by bST but was unaffected by ruminally protected AA. Milk yield was increased by bST but was not altered by ruminally protected AA compared with the control diet. The bST tended to increase percentages of fat and total solids in milk and increased yields of fat, protein, 3.5% fat-corrected milk, and total solids. Ruminally protected AA increased percentages of fat, protein, and total solids in milk; however, yields of milk components were unaffected by ruminally protected AA. Body weight and body condition scores were unaffected by treatment. Concentrations of essential AA in plasma were unaffected by bST administration. Ruminally protected Met and Lys increased the concentration of Met and tended to increase the concentration of Lys in plasma. The lack of an increase in yields of milk and milk protein when ruminally protected AA were fed suggests that adequate amounts of Met and Lys were supplied by the control diet and protein reserves of the cows to meet the AA requirements for synthesis of milk and milk components.     

Relationships among ewe milk production and ewe and lamb forage intake in Suffolk and Targhee ewes nursing single or twin lambs

Suffolk and Targhee ewes (30 each) with single or twin lambs were used in four periods beginning in late gestation and continuing through weaning to evaluate breed differences in milk production, lamb BW, and DMI by ewes and lambs. In Periods 1 (late gestation) and 2 (early lactation), ewes (Period 1) and ewes with lambs (Period 2) were individually penned, fed .45 kg of barley x ewe(-1) x d(-1) and allowed ad libitum access to chopped alfalfa. Ewes and lambs grazed native range in Periods 3 and 4. Grazed forage DMI was estimated using chromic oxide. Estimates of milk production were obtained by handmilking. Average lamb age was 4, 45, and 73 d at the beginning of Periods 2, 3, and 4, respectively. Milk production tended (P = .20) to be greater for Suffolk than for Targhee ewes. Targhee ewes produced 85% more (P = .001) wool than Suffolk ewes. From 33 d prepartum to 89 d postpartum, Suffolk ewes consistently weighed more (P = .001) than Targhee ewes. Suffolk ewe BW loss (-.15 kg/d) was greater (P = .01) than Targhee ewe BW loss (-.02 kg/d) from 33 d prepartum to 6 d postpartum. From 6 to 89 d postpartum BW gain did not differ (P = .69; .05 kg/d) between breeds. From birth to 89 d postpartum, Suffolk lambs consistently weighed more than Targhee lambs (P = .003). From birth to 89 d postpartum, ADG was greater for Suffolk than for Targhee lambs (P = .006). Targhee ewes consumed 25% more (P = .01) feed over the course of the study than did Suffolk ewes. Grazed forage DMI by Targhee lambs was 26% greater (P = .01) than DMI by Suffolk lambs. When meat production is the primary income from sheep, one potential advantage of Suffolks compared with Targhees is more rapid gain with less feed intake.     

The empirical impact of bovine somatotropin on New York dairy farms

Data from 259 farms that participated in the Cornell University Dairy Farm Business Summary Project were used to measure the impact of bovine somatotropin (bST) on milk production and profitability per cow. Linear regression was used to estimate the response to bST when other variables were held constant. Bovine somatotropin was a dummy variable for bST use or nonuse in the equations. For farms that used bST on 25% or more of the cow days in 1994, milk production increased by 510 kg per cow. Returns above purchased feed costs increased $153 per cow for farms that used bST. Milk receipts over operating costs increased $120 per cow for farms that used bST. The use of bST was estimated to increase net farm income by $27 per cow, but this estimated coefficient was not statistically different from 0. Differences in costs for labor or veterinary services per cow were not significantly different between farms that used bST and farms that did not use bST.     

Effects of feeding level on growth, composition of gain, carcass quality and mature body size in steers at ages up to six years

Tissue gain and efficiency and carcass characteristics of seventy-eight Angus steers were compared on three feed intake regimens and serially slaughtered at 6 months to 6 years. The regimens were: (A) continuous ad ad libitum feeding, (B) restricted to gain about 0.45 kg daily and (C) restricted as in B until 6 months before slaughter then fed ad libitum. Steers, regardless of feeding regimen, made their greatest gains up to 12 months of age and became less efficient after that time. Steers fed ad libitum had the highest percentage of fat but the lowest percentage of lean and bone when compared with steers fed for restricted gain. Carcasses of the steers fed ad libitum contained more lean and fat at each slaughter age. Average daily gain, feed efficiency and percentage of lean and bone decreased with age; and feed intake, slaughter grade, dressing percent, taste panel desirability and percent of fat tended to increase with age. All steers reached their maximum growth in height at withers, depth of chest and length of body at about 3 years. Steers that were restricted up to 6 months before slaughter showed compensatory growth during their ad libitum feeding period and during the first 12 months of the study; protein and fat were produced most efficiently by this growth. It would appear that it is possible to modify fat deposition by changing feed intake level.     

Recombinant bovine somatotropin and clinical mastitis: incidence, discarded milk following therapy, and culling

Holstein cows (n = 555) from four Michigan dairy farms were randomly assigned to receive bovine somatotropin (bST) or to serve as untreated controls. Bovine somatotropin (500 mg) was administered every 14 d beginning at 63 to 69 d of lactation and continuing until approximately 21 d prior to dry-off or until the cow was removed from the herd. Trial objectives were to determine the effect of bST on the incidence of clinical mastitis, number of days that milk was discarded because of therapy for clinical mastitis, and culling for mastitis. A total of 127 (22.9%) cases of clinical mastitis occurred during lactation. In the pretrial period (before 63 to 69 d of lactation), 42 (33.1%) cases occurred, and 85 (66.9%) cases occurred during the trial. Of the 42 pretrial cases, 57.1% occurred in control cows, and 42.9% occurred in treated cows. Of the 85 trial cases 47.1% occurred in control cows, and 52.9% occurred in treated cows. Using logistic regression, the odds ratio for the occurrence of clinical mastitis in treated cows was 1.06 (95% confidence interval = 0.62 to 1.81). The number of days that milk was discarded following therapy for clinical mastitis and the culling rate for mastitis did not differ between study groups.     

Insulin-like growth factors in plasma and afferent mammary lymph of lactating cows deprived of feed or treated with bovine somatotropin

The galactopoietic actions of bovine somatotropin are both direct and indirect. Indirect actions are apparently mediated by the insulin-like growth factor (IGF) system. The objective of this study was to compare systemic (plasma) versus local (lymph) concentrations of IGF. Afferent mammary lymph most nearly represents the extracellular fluid that is bathing mammary tissue. Catheters were surgically implanted in the jugular vein and the superficial afferent mammary lymph vessels of four lactating cows. A crossover design was utilized to evaluate the effects of bovine somatotropin (bST). After 2 d of basal sampling, either bST (40 mg/d) or excipient was administered daily for 5 d. After the conclusion of the bST study, a second study was conducted in which cows were deprived of feed for 36 h. Blood and lymph were simultaneously sampled at least every 6 h throughout both studies. Milk yield was increased by bST, and concentrations of IGF-I were increased in plasma and lymph. The relationship between plasma and lymph concentrations for IGF-II, bST, insulin, glucose, urea nitrogen, and nonesterified fatty acids were similar during bST treatment. Milk yield was reduced 76% by 36 h of feed deprivation. Feed deprivation also caused a reduction of IGF-I in plasma, but concentrations of IGF-I in lymph were not altered. In contrast, changes in IGF-II, bST, insulin, glucose, urea nitrogen, and nonesterified fatty acids that were caused by feed deprivation followed similar patterns in plasma and lymph. Clearly, if IGF-I mediates the mammary actions of bST, then concentrations of IGF-I in plasma correlate with milk yield responses as well as, if not better than, concentrations in lymph.     

Evaluation of the ovine callipyge locus: II. Genotypic effects on growth, slaughter, and carcass traits

A resource flock of 362 F2 lambs provided phenotypic and genotypic data to estimate effects of callipyge (CLPG) genotypes on growth, slaughter, and carcass traits. Lambs were serially slaughtered in six groups at 3-wk intervals starting at 23 wk of age to allow comparisons at different end points. Probabilities of CLPG genotypes were calculated at a position 86 cM from the most centromeric marker of chromosome 18. A contrast of CLPG genotypic effects, based on the paternal polar overdominance model, was used to evaluate callipyge and normal phenotypes. Relationships of traits with slaughter age, carcass weight, or 12th-rib fat depth for callipyge and normal phenotypic groups were estimated by regression. Callipyge and normal lambs did not differ for growth traits measured from birth to slaughter. Callipyge lambs produced 55.9% of live weight as chilled carcass weight compared with 51.7% for normal lambs at the same mean live weight of 48.32 kg. Lighter pelt, kidney-pelvic fat, and liver weights contributed to this advantage of callipyge lambs for dressing percentage (P < .001). Estimated accretion rates of carcass protein at the mean slaughter age were 12.5 and 10.2 g/d for callipyge and normal carcasses, respectively. Corresponding values for carcass fat were 35.2 and 42.1 g/d. Compositional differences in favor of callipyge carcasses were detected at constant values of slaughter age, carcass weight, and 12th-rib fat depth. Callipyge carcasses had 2.56 kg greater fat-free lean and 1.39 kg less fat than normal carcasses at the same mean age of 214.9 d (P < .001). The majority of these differences were established before the initial group was slaughtered and were maintained as age increased. Callipyge carcasses consisted of 24.3% fat and 71.3% fat-free lean, compared with 31.5 and 64.0% for normal carcasses at 25.6 kg of carcass weight. When evaluated at .49 cm of 12th-rib fat depth, callipyge lambs were 15.4 d older and produced 4.1 kg heavier carcasses with 4.3% less fat (P < .001). Effects of CLPG genotypic groups on carcass composition were greater than virtually all reported breed substitution effects. Use of the CLPG mutant allele in structured mating systems can dramatically increase production of lean lamb.     

Oxygen consumption by and blood flow across the portal-drained viscera and liver of pregnant ewes

The energy requirement of ewes increases during pregnancy. In late pregnancy, approximately 40% of the increase in heat production can be attributed to increases in heat production by nonreproductive tissues. The objective of this study was to determine the pattern of oxygen consumption by the portal-drained viscera (PDV) and liver during pregnancy to allow for an estimation of the extent to which these tissues contribute to the increase in energy requirement. Nineteen multiparous ewes were individually penned and allowed ad libitum access to an alfalfa hay-based diet. Catheters were surgically placed in the portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta. Oxygen consumption by the PDV and liver were subsequently measured before breeding and at 6, 19, 39, 61, 82, and, 103 d before lambing. Hepatic arterial blood flow was not influenced by litter size (P = .89) or stage of pregnancy (P = .28). Portal and hepatic venous blood flow peaked 19 d before lambing. Oxygen consumption by the PDV and liver increased with increased ad libitum feed intake. The increase in hepatic oxygen consumption occurred approximately 63 d earlier in ewes with twins than in ewes with a single fetus independent of changes in feed intake. Hepatic oxygen consumption increased with duration of gestation and was estimated to account for 40% of the heat production not associated with the gravid uterus.     

Ovarian follicular populations in lactating dairy cows treated with recombinant bovine somatotropin (sometribove) or saline and fed diets differing in fat content and energy

Interactions of dietary energy and fat with recombinant bST (sometribove) injections were tested for their effects on ovarian function. Lactating dairy cows were fed one of three diets differing in energy concentration (NEL) and percentage of DM of calcium salts of long-chain fatty acids: diet 1, 1.68 Mcal/kg and 0%; diet 2, 1.68 Mcal/kg and 2.2%; and diet 3, 1.78 Mcal/kg and 2.2%. Cows were injected daily with bST or saline during one of two 19-d interestrous periods (crossover design) in which ovarian follicles were measured by ultrasonography. The bST-treated cows produced more FCM and were in lower energy balance than saline-treated cows. Before d 12 (first follicular wave, estrus = d 0), bST-treated cows had more ovarian follicles in classes 1 (3 to 5 mm; cows on diet 3) or 2 (6 to 9 mm; cows on diets 1 and 2) than saline-treated cows. After d 12 (preovulatory follicular wave), numbers of follicles in different size classes were similar for bST-treated and saline-treated cows, but cows fed diet 2 had larger preovulatory follicles. Lower dietary energy and bST treatment were both associated with larger subordinate follicles. Ovarian follicles less than 10 mm were stimulated by bST, and calcium salts of long-chain fatty acids increased diameters of preovulatory follicles.     

Recombinant bovine somatotropin increases milk yield and calf gain in diverse breeds of beef cattle: associated changes in hormones and indices of metabolism

In Exp. 1, Angus (A, n = 30), Charolais (C, n = 37), and Simmental (S, n = 30) multiparous cows received (s.c.) recombinantly derived bovine somatotropin (bST; sometribove, 500 mg) or vehicle (VEH) at 2-wk intervals from 124 to 228 d postpartum (DPP). Calves were weaned at 228 DPP. Bovine somatotropin increased (P < .01) milk yield and percentage of milk fat similarly in A, C, and S cows. Calf weaning weight was greater (P < .05) in cows treated with bST than in those given VEH. Administration of bST decreased deposition of fat and increased concentrations of IGF-I, insulin, glucose, and nonesterified fatty acids. In Exp. 2, we compared effects of bST initiated before or after the breeding season. Charolais (n = 33) and S (n = 40) cows were administered (at 2-wk intervals) VEH or bST beginning at 28 DPP (B-bST) or bST beginning at 105 DPP (A-bST). Calves were weaned at 243 DPP. Administration of bST before or after the breeding season increased milk yield on DPP 136 and 194; however, yields were greater in A-bST than in B-bST cows. Milk yields were similar in all cows at 236 DPP, corresponding to decreased forage availability. Calf body weight was greater (P < .05) in A-bST than VEH; B-bST calves were similar to VEH. Fat depth was greater in VEH than in bST-treated cows in C but not in S cows. Serum IGF-I was greater in A- and B-bST than in VEH cows. Mean days from calving to serum progesterone > 1 ng/mL and pregnancy rates were similar in VEH, A-, and B-bST cows. Administration of bST increased cow milk yield and subsequent calf weaning weight when initiated after 100 d postpartum. As anticipated, bST increased IGF-I, insulin, glucose, and nonesterified fatty acids. Administration of bST before and during the breeding season did not affect reproductive performance.     

Pregnancy increases ovine uterine artery endothelial cyclooxygenase-1 expression

During normal pregnancy, and especially in the third trimester, both uterine blood flow and prostacyclin production by ovine uterine arteries are dramatically increased. We sought to determine if this is due, in part, to an increase in cyclooxygenase (COX) expression in the uterine artery endothelium. In this study we compared COX expression in uterine artery endothelium from nonpregnant and third-trimester pregnant (110-142 days' gestation) ewes. COX-2 expression was not detectable by Western blotting in uterine artery endothelium or vascular smooth muscle (VSM). In contrast, COX-1 expression was clearly observed in uterine artery. Immunohistochemical localization of COX-1 was endothelium > VSM, with both cell types showing an increase in COX-1 during the third trimester of pregnancy. COX-1 protein and messenger RNA (mRNA) levels were also detectable in collagenase dispersed endothelial cells, with expression of COX-1 in uterine artery endothelial cells dramatically increased during the third trimester of pregnancy at both the level of protein (346.4 +/- 28% of nonpregnant controls, P < 0.0005) and mRNA (51.04 +/- 7.98-fold of nonpregnant controls, P < 0.001). We conclude that the pregnancy-induced increases in prostacyclin production by uterine arteries is largely due to a dramatic increase in expression of COX-1 mRNA and associated protein predominantly occurring in the uterine artery endothelium and, to a lesser extent, in the VSM.     

Effect of the use of bovine somatotropin on culling practices in thirty-two dairy herds in Indiana, Michigan, and Ohio

Data from 5468 Holstein dairy cows in 32 herds were used to determine the effect of the use of bovine somatotropin (bST) on culling practices over a 13-mo period. After an initial herd inventory, monthly information regarding cow entry and exit from the herds was obtained by seven participating veterinarians. Culling was coded by farmers for the following reasons: low production, reproduction, somatic cell count, mastitis, sickness, dairy purposes, lameness, death, and other. In the control herds, cows were not treated with bST during the trial. Adopter herds were defined as herds that utilized supplemental bST for > or = 25% of the cow-days during the trial. Mean herd use of bST in adopter herds was 38.6%. No difference in the number of cows culled per cow-day at risk was detected between control and adopter herds (0.09 and 0.11%, respectively). Amount of in-herd use of bST was unrelated to culling. No significant differences were determined between adopter and control herds in the percentage of cows that were culled for any of the nine possible culling reasons. The results of this study suggest that culling patterns in herds that use bST are unaffected for at least the first year after adoption.     

The effect of bovine somatotropin and diet on somatotropin binding sites in hepatic tissue of lactating dairy cows

In the lactating cow, galactopoiesis is stimulated by treatment with recombinant bovine somatotropin (bST) and by an improved plane of nutrition. The present study determined the interaction between these variables and examined whether a positive galactopoietic effect was accompanied by a change in hepatic binding sites for bST. Lactating dairy cows received one of three diets with increasing nutrient density; diet 1, 150 g/kg of dry matter (DM) of crude protein (CP) and 10.5 MJ/kg of DM of metabolizable energy; diet 2, 170 g/kg of DM of CP and 11.3 MJ/kg of DM of metabolizable energy; and diet 3, 190 g/kg of DM of CP and 12.1 MJ/kg of DM of metabolizable energy. At 90 d after calving, half of the cows in each dietary group were treated with bST every 14 d for the rest of the lactation. Both nutrient density and administration of bST increased milk yield significantly in mid and late lactation; there was no significant treatment by diet interaction. Treatment with bST significantly increased plasma concentrations of insulin-like growth factor (IGF)-I compared with IGF-I concentrations in controls in both mid and late lactation. Comparisons within diet revealed that concentrations of IGF-I were significantly higher in cows fed diet 3 than in cows fed diets 1 and 2 at both stages of lactation. Increases in plasma insulin were confined to cows in late lactation, and no changes were observed for nonesterified fatty acids. Liver biopsies showed that concentrations of hepatic binding sites for bST were not affected significantly by bST treatment but were increased in midlactation for cows fed diet 3. Concentration of hepatic binding sites per unit weight of tissue were greater for cows in midlactation than for cows in late lactation. In summary, exogenous bST treatment and increased nutrient density were associated with elevated plasma IGF-I concentrations and increased milk yield; however, only nutrient density in midlactation increased the number of hepatic binding sites for bST. Exogenous bST treatment had relatively little effect on the concentration of hepatic bST receptors compared with nutrient density.