The Growth and Composition of Wool II. The Effect of Casein, Gelatin, and Sulphur-Containing Amino Acids Given Per Abomasum

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Abstract
The effect on wool growth and the sulphur content of wool of abomasal supplements of casein, gelatin, and of L-cysteine and DL-methionine added to the proteins has been examined. The supplements were administered as a continuous infusion over a period of 10-12 hr each day. Supplements of 60 g casein/day, given to 3 sheep for 9 weeks, resulted in substantial increases in wool growth (123-181%). In contrast 60 g gelatin/day increased wool growth by only 17-24%. When sulphur-containing amino acids (S-amino acids) were added to the proteins wool growth was further increased (16-37%). The percentage of the supplementary S-amino acids which could be accounted for in the wool grown during supplementation was high, viz. 48-51% of the S-amino acids in casein, 29-35% of the S-amino acids in gelatin, and 13-35% of the supplements of cysteine or methionine. An increase in fibre cross-sectional area accounted for c. 30-40% of the increase in wool growth during supplementation with protein or protein plus S-amino acid. In some sheep a much higher proportion of the increase in wool growth, due to S-amino acids alone, could be accounted for by an increase in cross-sectional area. The S content of the wool was increased 9-19% during casein supplementation, but was not increased during gelatin supplementation. During protein plus S-amino acid supplementation the S content of the wool was increased 17-30%. There was a consistent increase in the dry matter digestibility of the basal diet during the infusion of gelatin or casein into the abomasum. The mean dry matter digestibility was 55. 0% on the basal diel alone and 57. 8% during protein supplementation. It is concluded that the substantial increases in wool growth rate obtained during casein supplementation per abomasum are due specifically to essential amino acids. Previously observed effects of S-amino acids on wool growth and S content of wool have been confirmed.