Recombinant bovine somatotropin: Association with reproductive performancein dairy cows

A clinical trial was performed to determine the effect of bST on reproducti ve performance in dairy cows on 4 Michigan dairy farms when bST was used ac cording to labeled directions. Holstein cows (n = 555) at 4 Michigan dairy farms were randomly assigned to receive bovine somatotropin (bST) or to ser ve as untreated controls. Bovine somatotropin (500 mg, SC) was administered every 14 d beginning at 63 to 69 d of lactation and continuing until appro ximately 21 d prior to the end of lactation or until the producer removed t he animal from the herd. A total of 229 (42.57%) animals consisting of 112 (48.91%) controls and 117 (51.09%) bST-treated cows were not diagnosed preg nant and were considered as having reproductive failure by 150 d of lactati on and 92 (17.10%) of the animals consisting of 45 (48.91%) controls and 47 (51.09%) bST-treated cows had reproductive failure at the end of their lac tation. No significant difference in the incidence of reproductive failure existed between the study treatment groups during either time frame. Cows w ith cystic ovarian disease had more instances of reproductive failure at 15 0 d of lactation than cows without this disease. Cows with dystocia, twin b irths, metritis, displaced abomasum and cystic ovarian disease had more ins tances of reproductive failure by the end of lactation than cows without th ese diseases. The bST-treated cows developed more nonspecific off feed cond itions during the study lactation and had more twin births at the calving f ollowing bST administration compared to control cows. No differences were f ound between the study treatment groups in calculations of reproductive par ameters. Logistic regression analysis found no significant effect of bST on reproductive failure; the odds ratios for the bST treatment effect on repr oductive failure at 150 d of lactation and reproductive failure at the end of lactation were 0.95 (95% CI 0.67 to 1.36) and 0.95 (95% CI 0.59 to 1.54) , respectively. Overall, bST was not found to have a significant impact on reproductive performance in the herds studied. (C) 1999 by Elsevier Science Inc.