The net efficiency of dietary protein for wool production is 0.2-0.25 in sheep, 0.39 in Angora goats and 0.43 in Angora rabbits.
Maximum wool growth demands a high level of dietary protein, and, the requirements for the amino acids Met and Cys are usually above exogenous supply. Supplementation with Met enhances efficiency of protein for wool growth by promoting protein metabolism in the follicles, skin and whole body. Supplementing with Cys is less effective but increases wool growth rate and sulphur content in wool. Supplying other amino acids appears to have little effects on wool production. Cys synthesized in the skin is quantitatively important to support wool growth. However, its synthesis competes for Met against the synthesis of polyamines. Polyamines are essential to maintain high proliferation rate of bulb cells and their concentrations are associated with growth rate of fibre length under experimental conditions. Remethylation and transamination play little role in Met catabolism in the skin. Wool growth could be maximized when Met is partitioned at appropriate proportions to protein, Cys and polyamine syntheses, particularly in the skin. Skin and wool follicles do not show a direct response to nutrient-partitioning hormones and respond passively to hormone-induced nutritional changes. Dietary manipulation of amino acid supply for a better utilization for wool growth is effective, but genetic selection for a high efficiency appears to be a more economical strategy.
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