Conception rate, growth, and lactation of dairy heifers treated with recombinant somatotropin

Eighty Holstein heifers (295 kg; 13 to 16 mo of age) were allotted to two treatments in a completely random design experiment to determine the effect of daily injections of recombinant bovine somatotropin on conception, growth, and subsequent lactation. Heifers were treated with either 41.2 mg of bovine somatotropin or saline daily for 5 mo. Breeding was initiated 2 mo after the start of bovine somatotropin or saline treatment. Conception rates and number of services per conception did not differ between treatments. During the injection period, heifers treated with bovine somatotropin gained .18 kg/d faster than control heifers. During the 5 mo following the treatment period, control heifers gained .12 kg/d faster than the heifers that had received bovine somatotropin so that at the end of this 10-mo period weights of heifers in the 2 groups were similar. The heifers treated with bovine somatotropin had a greater increase in both hip height and pelvic size compared with control heifers during the 5-mo treatment period. Calving difficulty scores were similar between treatments. Treatment with bovine somatotropin prior to and during breeding of these heifers did not affect milk yield after first calving compared with control heifers.