Interactions of bovine somatotropin and nutrition on milk production and composition of dairy cows.
48 multiparous Holstein cows were used in a 2 × 2 factorial to study interactions of bovine somatotropin (GH) and nutrition during wk 5-20 post partum. Main effects were GH (±10.3 mg/day) and diet (control, C; or high-protein and energy, HPE). Diet C contained 16.3% CP and 1.65 Mcal net energy for lactation (NEL) per kg, while diet HPE contained 18% CP and 1.74 Mcal NEL per kg, with additional energy as fat from extruded soyabeans and Megalac®. Diets were 50:25:25 concentrate:lucerne:maize silage (DM basis). GH increased yields of milk (37.9 vs. 40.9 kg/day, PPPPPP>0.10) with HPE+ (3.07, 3.00, 2.81 and 2.86). DM intake was not significantly (P>0.10) affected by GH (22.8 vs. 23.5 kg/day), but was lower (P