Effect of virginiamycin and bovine somatotropin on growth, nutrient conversion and brood parameter in young female calves

Experiments were conducted on 20 female calves (Bohemian red spotted x Friesian), housed in individual stables and offered milk, concentrate mixture and hay to meet the nutrient requirements for maintenance and growth at 85% of NRC (1978) recommended requirements. Calves, initially 21 to 24 days old, were allotted to four different treatments. Calves in the first group were treated subcutaneously with olive oil at 7 day intervals (control). The second group received injections of olive oil and a daily oral dose of virginiamycin (a feed antibiotic), 80 mg per animal. The third group received subcutaneous (sc) injections of recombinant methionyl bovine somatotropin (bST) in a sustained-release vehicle (100 mg per head) in 7 day intervals. The fourth group received both virginiamycin and bST. The experiment lasted for 70 days. Control calves gained, on average, 0.52 kg.day(-1). Both growth promoters appeared to improve weight gain and feed efficiency. The effects of virginiamycin and bST were additive. Virginiamycin, bST and a combination of bST and virginiamycin improved gains by 9.6, 5.8 and 15.4%, respectively. Only the effect of bST and virginiamycin in combination, however, was significant (P < 0.05). Blood haemoglobin and serum glucose, protein and cholesterol were not significantly affected. The plasma bST concentration was up to ten-fold higher in the bST-treated groups then in the control and virginiamycin-treated groups. The effect of virginiamycin on the plasma bST concentration was not significant.