Nitrogen Metabolism in Nonruminant Herbivores. I. The Influence of Nonprotein Nitrogen and Protein Quality on the Nitrogen Retention of Adult Mares

Abstract

THE capacity of ruminants to utilize efficiently forages low in protein or diets based on nonprotein nitrogen (NPN) has been studied extensively and was reviewed by McDonald (1968), Oltjen (1969) and Tillman and Sidhu (1969). Nonruminant herbivores are also capable of successfully utilizing low quality roughages by virtue of the adaptation of the digestive tract in the region of the large intestine which allows a microbial fermentation similar to that in ruminants to proceed (Alexander, 1954). For example, in the Equidae the production of volatile fatty acids and their subsequent absorption from the large intestine was established by Barcroft, Mc-Annally and Phillipson (1944) and synthesis of the B-vitamins and subsequent absorption was demonstrated by Carroll, Goss and Howell (1949). However, surprisingly little is known about the utilization of microbial protein in the Equidae. The present studies were undertaken with three objectives: (1) to determine the capacity of horses to utilize complete and deficient proteins; (2) to study the ability of horses to utilize urea as a source of dietary nitrogen; (3) to establish the daily maintenance requirement of adult Thoroughbred mares for nitrogen, using nitrogen balance as the criterion of dietary adequacy as well as efficiency of nitrogen metabolism. Copyright © 1970. American Society of Animal Science . Copyright 1970 by American Society of Animal Science