Effects of rumen-degradable protein concentration in diets on digestion, nitrogen utilization and milk yield by dairy goats

Abstract

Up to the present, nitrogen requirements of goats have generally been estimated using crude or digestible crude protein. We attempted to quantify these requirements more precisely by measuring the effects of different levels of rumen-degradable protein (RDP) in the diet, keeping the level of nondegradable protein constant. In an experiment with lactating goats, when dietary concentration of RDP was varied between 6.7 and 9.7% of dry matter (crude protein content was 11.7 and 14.7% in dry matter), feed intake and digestibilities of organic matter and crude fiber were not changed. Urinary nitrogen increased with higher RDP level, but milk yield and milk nitrogen content did not change. Milk urea level increased. In another experiment with a lower level of RDP (5.1% in 11.9% crude protein), feed intake was significantly depressed although digestibilities of organic matter and crude fiber were not different. Energy and nitrogen retention decreased significantly.