Responses of Dairy Cows in Early Lactation to Bovine Somatotropin and Ruminally Inert Fat

Abstract

Bovine somatotropin (0 or 41.2 mg/d bST) and calcium salts of long-chain fatty acids (0 or .77 kg/d Ca-LCFA) were administered to 16 Holstein cows in early lactation. Cows remained on 0 or 41.2 mg/d bST for the entire 10 wk and received 0 or .77 kg/d Ca-LCFA in one of two 5-wk periods. Production data were recorded daily, milk fatty acids, and blood metabolites were determined once each period. Treatments did not affect feed intake. Fat-corrected milk (kg/d) and percentage of milk fat for cows receiving no supplementation, fatty acids alone, bST alone, and fatty acids and bST together were 33.8, 3.2; 33.5, 3.1; 37.4, 3.4; and 40.8, 3.5. Milk fatty acids below C16 were reduced with either bST or dietary fatty acids; C16 fatty acids were lower with bST but higher with dietary fatty acids; C18:0 fatty acids were reduced with dietary fatty acids; and C18:1 fatty acids were higher with either bST or dietary fatty acids. Blood acetoacetate concentrations were higher with both bST and dietary fatty acids, β-hydroxybutyrate was not different, and FFA and insulin concentrations increased with bST. In this experiment, the energy supplied by Ca-LCFA acids enhanced the lactogenic effect of bST.