Effects of Treatment of Dairy Cows with Recombinant Bovine Somatotropin over Three or Four Lactations

Abstract

Jersey, Dutch Red and White, and Friesian cows were subcutaneously injected with 640mg of recombinant bST at 28-d intervals from 87 to 115 d after calving through four successive lactations. A TMR (6.72 MJ of NEL and 168g of CP/kg of DM) was fed for ad libitum consumption. The bST effects per day were 3.3kg for milk yield, 189g for fat yield, 109g for protein yield, 157g for lactose yield, 4 MJ of NEL for feed intake, and –4kg for body weight. Responses in blood parameters measured 7 d after injection were –.007ml for glucose, –1.3mg of N/l00ml for urea, 221 μmol/L for 3-hydroxybutyrate, 59 μmol/L for NEFA, 65 ng/L for insulin, 2.8μg/L for thyroxine, and 26.7μg/L for somatotropin. Somatic cell count in milk was 75,000 cells/ml higher in treated cows. Concentrations of NEFA, Ca, Mg, and phosphorus were unaffected. Repeatability of the maximum response in milk yield after bST treatment was low: .2 within and .5 between lactations. Cows treated in the previous lactation had slightly more retained placentas, and birth weight of their calves was 2kg less. No differences were observed between treated and control cows in disease incidence. Six treated cows were culled in third and fourth lactations. No indications for tissue damage, inflammation, or stress after bST injections were detected.