Influence of Methionine and Tryptophan on Nitrogen Utilization by Lambs Fed High Levels of Non-Protein Nitrogen

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Abstract
Two digestion and nitrogen metabolism trials were conducted with grade wether lambs fed semi-purified rations composed of wheat straw, cane molasses and a concentrate mixture. The urea contained in the concentrate mixture was the sole source of supplemental nitrogen and accounted for 85% of the total nitrogen, which amounted to 1.6% of the ration. Substitution of either 1.5 gm. of DL-methionine or 0.8 gm. of L-tryptophan for isonitrogenous amounts of urea nitrogen increased (P<.05) the retention of absorbed nitrogen above that of lambs fed the urea-basal ration. However, lambs fed rations containing both amino acids did not retain more absorbed nitrogen than lambs fed rations containing either one. The average increase in retention of absorbed nitrogen by lambs fed rations containing either or both amino acids was 15% above that of lambs fed the urea-basal ration. This increase in nitrogen retention was not related to the adaptation of the lambs to NPN utilization associated with time. Supplementation of the urea-basal ration with either methionine or tryptophan did not influence the apparent digestibility of protein or the digestibility of organic matter and crude fiber. Copyright © 1965. American Society of Animal Science . Copyright 1965 by American Society of Animal Science