Lactational responses to postruminal administration of proteins and amino acids.

Rumen by-pass of nutrients has improved performance of lactating dairy cows, growing stepers, and sheep. Postruminal supplementation of casein has increased milk production 1 to 4 kg per cow per day and milk protein yield by 10 to 15%. Component(s) in casein eliciting the improved performance have not been determined adequately. Glucose, amino acids, hormone secretion, or a combination of these factors may be responsible for the improved performance. Future research to delineate limiting nutrients for postruminal supplementation should prove fruitful and should make a major contribution to improved production by ruminant animals.