ENERGY-METABOLISM OF LACTATING DAIRY-COWS IN RESPONSE TO LONG-TERM ADMINISTRATION OF BOVINE SOMATOTROPIN (BST)

16 lactating dairy cows received 6 injections at 4-wk intervals of either saline (control) or 640 mg of prolonged-release bovine Somatotropin (bST). The bST-treated animals were pair fed to the control group. Digestible and metabolizable energy were not affected by the treatment. The bST-induced increase of milk energy excretion was compensated by mobilization of body energy reserves with the consequence of decreasing body weight. The utilization of the metabolizable energy of the diet and the mobilized body energy for milk production and maintenance was unchanged. At high protein intake, bST increased milk N excretion at the expense of urinary N, while N balance was not affected. Daily milk yield of treated animals averaged 2,8 kg above the control level. The fat and protein content of the milk were not affected by bST.