Ration Factors Affecting the Utilization of Urea Nitrogen by Lambs

Abstract

The value of supplemental nitrogen added as urea to different basal rations containing about 7 percent protein was studied in a series of digestibility and nitrogen balance trials with lambs. The first experiment was conducted with three basal rations containing 84, 49 and 28 percent roughage supplied as cottonseed hulls, and a fourth ration containing 49 percent as prairie hay. The nitrogen content of the rations was made equivalent to 10 percent protein by supplementation with equal amounts of urea. Differences in nitrogen retention between the basal and urea-supplemented rations demonstrated that with decreasing hulls in the rations, increasing amounts of urea nitrogen were retained. The 49-percent hay ration was equivalent to the 28-percent hull ration in supporting increased nitrogen retention. In the second experiment the protein equivalent of a basal ration containing 37 percent cottonseed hulls was increased to 8.5, 10.1 and 12.3 percent by addition of urea, and to 8.4 and 12.2 percent by substitution of cottonseed meal for carbohydrate feeds. Maximum nitrogen retention with the urea-supplemented rations was reached at the 10 percent protein level. A slightly higher retention was attained with the cottonseed meal ration at the 12 percent level. In the third experiment comparisons were made with three basal rations containing cottonseed meal, soybean oil meal, and corn gluten meal. Without supplementation, these rations permitted similar nitrogen retentions. Equal amounts of urea added to the rations induced similar increases in nitrogen retention. In all experiments urea increased the digestibility of the rations.