Influence of sometribove, USAN (recombinant methionyl bovine somatotropin) on the body composition of lactating cattle.

Ten cattle were injected with 40 mg/d sometribove (United States adopted name for recombinant methionyl bovine somatotropin) in bicarbonate buffer, and nine with the bicarbonate buffer only. These treatments continued from the first day of wk 11 of lactation through the end of wk 18 of lactation. Deuterium oxide (D2O) dilution was used to estimate D2O space at wk 10 and 18. All cattle were fed a dry, complete diet containing 2.9% nitrogen, and an estimated 1.7 Mcal/kg net energy for lactation (NE1). After 18 wk of lactation, carcass composition was determined from carcass density and the composition of the rest of the body was determined by direct chemical analyses. Regression equations were constructed relating chemical composition at 18 wk to D2O space and live body mass. These equations were used to estimate body composition at wk 10. The estimated wk 10 composition was used to adjust wk 18 body composition for pretreatment inter-animal variation. Treatment with sometribove resulted in increased milk production (34.3 kg/d vs. 30.2 kg/d), foregut tissue (25.2 kg vs. 23.2 kg), foregut contents (72.0 vs. 62.1 kg), and reduced total body fat (28.3 vs. 45.7 kg), body energy (760 vs. 916 Mcal) and visceral fat mass.