Metabolic and yield responses of multiparous holstein cows to prepartum rumen-undegradable protein

Abstract

The effects of concentration of rumen-undegradable protein (RUP) in prepartum diets on performance and metabolic measures were determined. Pregnant, nonlactating cows were assigned to one of three dietary treatments that differed in concentrations of crude protein and RUP. The crude protein and RUP percentages (dry matter basis) in the diets were 11.7 and 3.1%, 15.6 and 6.8%, and 20.6 and 10.6%, which were identified as low, medium, and high protein diets, respectively. Dietary treatments were initiated 6 wk prior to expected calving date and were fed until parturition. All cows were fed similar postpartum diets through wk 10 of lactation. Prepartum intakes of dry matter and rumen-degradable protein were similar among treatments. Yields of milk, protein, and fat were not affected by prepartum RUP. Concentrations of plasma urea N in cows fed the medium and high protein diets were elevated during the prepartum period even though intakes of rumen-degradable protein were similar for cows on all treatments. Cows fed the medium and high protein diets had greater prepartum concentrations of Val, Ile, and Leu but not other essential amino acids in plasma. Dietary treatments did not affect prepartum or postpartum contents of triglycerides in liver or plasma nonesterified fatty acid concentrations. Thus, supplemental RUP fed to cows for 6 wk prepartum affected protein metabolism but not measures of energy metabolism.