Glucose kinetic responses to protein supplementation and exogenous somatotropin in late gestation dairy cows

Glucose kinetics were measured in late gestation multiparous Holstein dairy cows fed diets with different amounts of dietary crude protein (13.3 vs. 17.8%), with and without exogenous somatotropin. The trial was conducted as a completely randomized design; 35 cows were used in the final analysis. Kinetic measurements were made using the single injection technique with uniformly labeled ¹³C-labeled glucose. A diet that contained 17.8% crude protein appeared to increase glucose utilization without a corresponding increase in supply. The evidence was an increased rate of glucose disposal. In contrast, exogenous bovine somatotropin (Posilac^®, Monsanto Co., St. Louis, MO) appeared to enhance glucose conservation, as indicated by a tendency for a decreased fractional catabolic rate and an increased glucose pool size. Somatotropin appeared to modify glucose metabolism in a pattern favorable for supporting terminal fetal development and lactogenesis and for maintaining or enhancing maternal glycemia. The latter pattern could have implications for improving the health of periparturient dairy cows.