Abstract
Experiments were conducted to determine if post-ruminal availability of either sulfur amino acids or total protein were limiting for wool growth and body weight gain in lambs fed a 75% concentrate diet containing 8 or 12% crude protein. Replacement of 4% dietary casein with an equal amount of casein previously treated with 10 volumes of a 4% formaldehyde solution improved growth rate 20% and feed efficiency 8%. The dietary addition of 0.3% methionine or methionine hydroxy analog significantly improved growth rate and feed efficiency of lambs fed an 8% crude protein diet but not those fed a 12% crude protein diet. Daily intraperitoneal injections of 1.5, 3.0 or 4.5 g methionine or the dietary addition of 0.3% methionine or methionine hydroxy analog significantly increased wool growth rate of lambs fed both the 8 and 12% protein rations. These data demonstrate that total postruminal availability of certain amino acids, present in casein, were limiting for maximum growth and feed efficiency in lambs fed a 12% native protein diet and that sulfur amino acids are specifically limiting for maximal wool growth. Sulfur amino acids were also first limiting for growth and feed efficiency in lambs fed an 8% protein diet. Copyright © 1971. American Society of Animal Science. Copyright 1971 by American Society of Animal Science.

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