This manuscript presents the results of a review of the effects of recombinant bovine somatotropin (rBST) on dairy cattle health, reproductive performance, and culling, that was carried out by an expert panel established by the Canadian Veterinary Medical Association (CVMA). The panel was established by the CVMA in response to a request from Health Canada in 1998 and their report was made public in 1999. A series of meta-analyses was used to combine data on health-related parameters that were extracted from all randomized clinical trials that had been published in peer-reviewed journals or which were provided by Health Canada from the submission by Monsanto for registration of rBST in Canada. A companion paper (1) presents the estimates of the effect of the drug on production parameters. Recombinant bovine somatotropin was found to increase the risk of clinical mastitis by approximately 25% during the treatment period but there was insufficient data to draw firm conclusions about the effects of the drug on the prevalence of subclinical intra-mammary infections. Use of rBST increased the risk of a cow failing to conceive by approximately 40%. For cows which did conceive, there was no effect on services per conception and only a small increase in average days open (5 days). Use of the drug had no effect on gestation length, but the information about a possible effect on the risk of twinning was equivocal. Cows treated with rBST had an estimated 55% increase in the risk of developing clinical signs of lameness. Few studies reported data on culling, but based on those that did, there appeared to be an increase risk of culling evident in multiparous cows. Use of the drug in 1 lactation period appeared to reduce the risk of metabolic diseases (particularly ketosis) in the early period of the subsequent lactation.

Newborn foals of mares grazing on Acremonium coenophialum-infected fescue pasture throughout gestation or from gestation day 300 to parturition had increased gestation duration and decreased serum triiodothyronine concentration. Pregnant mares were allotted to 4 treatments: grazing continuously on endophyte-free (E-) fescue, grazing continuously on endophyte-infected (E+) fescue, grazing on E+ fescue from gestation day 300 to parturition, and grazing on E+ fescue from conception to gestation day 300. Morphometric studies indicated that foals born to mares exposed to endophyte late in gestation had large, distended thyroid follicles lined by flat cuboidal epithelial cells. Mean triiodothyronine concentration in foals exposed to endophyte (395.2 ng/dl) was decreased (P < 0.01), compared with mean values in control foals (778.0 ng/dl). Thyroxine and reverse triiodothyronine concentrations were not significantly different among groups. Foal organ weight as a percentage of foal body weight was not significantly different among experimental groups.

Objective--To evaluate the effects of diethylstilbestrol (DES) or alpha-zearalanol (zeranol) on fetal development, gestation duration, and number of offspring. Design-Study effects of prenatal administration of DES or zeranol on various pre- and perinatal variables in an experimental group of mice, compared with effects in a control group. Animal--Pregnant NMRI mice. Procedure--Diethylstilbestrol or zeranol (150 mg/kg of body weight) or vehicle (controls) was administered sc to pregnant mice on days 9 and 10 of gestation. Fetuses from pregnant mice of each group were counted and weighed, and their size and head length were recorded. Additional pregnant mice delivered their fetuses naturally, and pups from each group were counted and their sex was determined. At the end of gestation, abortions were evaluated. All data were statistically analyzed. Results--Mean number of fetuses was significantly lower (P < 0.0001) in DES-treated (4.59 +/- 0.48) than in control mice (8.33 +/- 0.49). Both estrogenic substances significantly reduced fetal size and weight (P < 0.0001), compared with control mice. Diethylstilbestrol significantly increased abortion frequency (P < 0.0001) and gestation duration (P < 0.0001), compared with values for control mice. A reduced number of live pups (P < 0.0001) from pregnant mice administered DES (5.48 +/- 0.38) or zeranol (5.97 +/- 0.49) was observed, compared with control mice (8.52 +/- 0.50), because of reduced number of male offspring (P < 0.0001). Conclusions--Diethylstilbestrol or zeranol administered during mid-pregnancy leads to decreased fetal weight and size and lower numbers of male offspring at birth. Likewise, DES induced a significant increase in abortions and gestation duration.

Cattle heterozygous for deficiency of uridine monophosphate synthase required more breeding services per calving when mated to other heterozygotes than did matings of normal cattle. Gestation length, number of breeding services per calving, and days from breeding to pregnancy examination were monitored on 759 complete gestations, 76 false-positive pregnancy diagnoses, 14 false-negative pregnancy diagnoses, and 413 negative pregnancy diagnoses in a dairy herd between 1983 and 1987. For complete gestations, 15 heterozygote X heterozygote matings required 3.13 +/- 0.37 breeding services per calving, which was significantly more than the 2.05 +/- 0.05 breeding services required for normal X normal matings; gestation length and days from breeding to pregnancy examination were similar between mating types. For false-positive pregnancy diagnoses, females diagnosed pregnant, but subsequently found not to be pregnant, 5 heterozygote X heterozygote matings averaged 51 +/- 23 days of gestation, which was less than the 93 +/- 6 days required for 71 normal matings; services and days from breeding to pregnancy examination were similar between mating types. All false-negative pregnancy diagnoses, females diagnosed not pregnant but later found to be pregnant, were made on cattle with normal matings. For negative pregnancy diagnoses, heterozygous matings averaged 0.3 more breeding services per examination than normal matings.

Primigravid swine were vaccinated orally with a live enterotoxigenic Escherichia coli (ETEC) strain that produces pilus antigen K99. The titers of K99 antibody in colostrum and milk of vaccinates remained higher than those of nonvaccinated controls through the first lactation after vaccination (4 weeks). Some control swine had low titers of K99 antibody in colostrum or developed low titers of K99 antibody in milk during lactation. Lacteal K99 antibody titers of vaccinates dropped to control levels during the second lactation, 6 months after vaccination. Pigs suckling vaccinates and controls were equally susceptible to challenge exposure to K99+ ETEC during the second lactation. Orally vaccinated swine given a parenteral booster vaccination (with killed K99+ ETEC) during their second gestation had K99 antibody in milk through their second lactation. During the second lactation, these orally vaccinated parenterally revaccinated swine had higher titers of K99 antibody in postcolostral milk than did nonvaccinated controls, controls given only the parenteral booster injection, or controls vaccinated parenterally during both gestations.