Effects of sustained release bovine somatotropin (sometribove) on animal health in commercial dairy herds

The health of dairy cows given bovine somatotropin (bST) for one lactation was evaluated in 28 commercial herds located in four regions of the United States. At least six herds were in a region and at least one herd/region co ntained fewer than 60 cows. Cows (n = 1213) were assigned randomly to contr ol or bST groups and were treated beginning in wk 9 to 10 of lactation and every 14 d until dry-off or d 400 of lactation. Management was according to site practices. Cows were observed for health-related signs by farm person nel daily and by the herd veterinarian biweekly. Average 305-d test-day mil k yields were 932 kg greater for bST-treated cows. Pregnancy rates, days op en, twinning, cystic ovaries, or abortions were unaffected by treatments. S upplementation of cows with bST had no effect on total mastitis cases, tota l days of mastitis, duration of mastitis, or the odds ratio of a cow to dev elop mastitis. Cows supplemented with bST used more medications for health events other than mastitis. This usage was associated primarily with treatm ents for disorders of the foot and hock. Supplemented cows had a slight inc rease in foot disorders. There was no effect of supplementation with bST on culling from the herd or removal from study. Overall, the results confirm that label directions for bST are adequate for safe use under field conditi ons. All clinical signs observed in this study occur normally in dairy herd s and were managed in cows supplemented with bST.