Effect of supplemental protein quality and evaporative cooling on performance of dairy cows during hot weather

Abstract

Two experiments were conducted. In experiment 1, diets were supplemented with blood, fish and soybean meals (HQ) or corn gluten meal (LQ) for similar CP and UIP, but differed in Lys%(HQ =.91; LQ =.59). Diets were fed to evaporatively cooled (EC) or non-cooled (S) cows. Milk yield was higher for HQ than LQ and for EC than S. Compared to S, EC cows tended to consume more feed and had lower rectal temperatures and respiration rates. Experiment 2 consisted of a metabolic and an in situ trial. Ruminal, postruminal and total tract digestibilities of DM on HQ and LQ diets did not differ, while postruminal digestibility of CP was higher for HQ than LQ. The pattern of EAA flowing to the duodenum was not affected by diets; however, after 24 h incubation in the rumen, residual Lys tended to be higher, but Leu and Phe lower for HQ than LQ. Rumen bypass of Lys is increased by feeding diets high in UIP and Lys, resulting in increased milk yields. (Abstract shortened with permission of author.)