The Influence of Dietary Nitrogen Source and Drinking Water pH on Growth, Digestibility, and Nitrogen Metabolism in Lambs Fed a High Roughage Diet

Abstract

The influence of drinking water pH and dietary nitrogen source on the growth and metabolism of young lambs fed a high roughage diet was examined in a series of trials. Two phases of a drylot feeding trial involved a comparison of diets in which all crude protein was derived from natural sources (NATURAL) or 25% of the crude protein equivalent was derived from urea (NPN). The third phase involved a comparison of NATURAL and NPN diets and drinking water of pH 5.5 to 6.0 or pH 9.0 to 9.5. Lambs tended to perform better on the NATURAL diet, largely due to increased feed consumption. Drinking water pH had no significant effects on performance. Twelve lambs were used in 3 successive metabolism trials. In trial 1 (NATURAL vs. NPN), no significant differences were observed in dry matter, organic matter, acid detergent fiber or cellulose digestibility. Nitrogen retention was similar for NPN-fed NATURAL-or NPN-fed lambs. Trials 2 and 3 compared NATURAL and NPN diets with pH 5.5 to 6.0 or pH 9.0 to 9.5 drinking water. Small but significant (P<.05) increases in dry matter, organic matter and cellulose digestion were observed with pH 9.0 to 9.5 drinking water in trial 2, and a similar effect was noted in NATURAL-fed lambs in trial 3. Nitrogen retention was not influenced by drinking water pH. These studies with high roughage diets indicate that drinking water pH would not appear to be a major concern in the management of rangeland ruminants.