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

The effects of concentration of rumen-undegradable protein (RUP) in prepart um diets on performance and metabolic measures were determined. Pregnant, n onlactating cows were assigned to one of three dietary treatments that diff ered 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 prot ein diets, respectively. Dietary treatments were initiated 6 wk prior to ex pected calving date and were fed until parturition. All cows were fed simil ar postpartum diets through wk 10 of lactation. Prepartum intakes of dry ma tter and rumen-degradable protein were similar among treatments. Yields of milk, protein, and fat were not affected by prepartum RUP. Concentrations o f plasma urea N in cows fed the medium and high protein diets were elevated during the prepartum period even though intakes of rumen-degradable protei n were similar for cows on all treatments. Cows fed the medium and high pro tein diets had greater prepartum concentrations of Val, lie, and Leu but no t other essential amino acids in plasma. Dietary treatments did not affect prepartum or postpartum contents of triglycerides in liver or plasma nonest erified fatty acid concentrations. Thus, supplemental RUP fed to cows for 6 wk prepartum affected protein metabolism but not measures of energy metabo lism.