Protein and sulphur amino acid nutrition of hair fibre-producing Angora and Cashmere goats

Abstract

The results from a number of studies are presented which investigated responses in fibre production of British Cashmere and Angora goats to variation in protein and sulphur amino acid nutrition under conditions of active fibre growth. Requirements for amino acids were considered in the context of the concentration of amino acids, including cysteine and methionine, in rumen microbial protein and in dietary protein supplements compared with the amino acid composition of hair fibre. Increases in fibre yield and diameter were consistently observed in Angora goats given good quality protein supplements or rumen-protected intestinally-available methionine (Smartamine™M, Rhône-Poulenc). Cashmere yield was not influenced by urea or white fishmeal supplementation but responded positively (in contrast to other studies in the literature) to additional dietary methionine. While responses in cashmere production have been recorded in response to protein supplementation at sub-maintenance levels of nutrition, it is suggested that one component of the absent or reduced response at above maintenance may be the smaller quantitative synthesis of this fibre compared with mohair production by Angora goats. The results are considered in the context of studies from the sheep literature in which protein and amino acid supplementation were shown to stimulate proliferation of hair forming cells in the wool follicle and to increase deposition of protein fractions containing high concentrations of sulphur-containing amino acids. Results from an in vitro study suggested that methionine could support cashmere fibre growth (approximately 0.75) in the absence of cysteine and cystine, providing evidence that methionine is essential for fibre production and that transulphuration occurs in isolated hair follicles. However, cysteine and cystine were also required to produce maximum growth. In the context of competition between the hair follicle and other body tissues, data are presented which illustrate the increases in nitrogen retention and/or anabolic growth response to protein or protected-methionine supplementation in non-integumental tissues of Cashmere and Angora goats also, despite the presence of lower concentrations of sulphur-containing amino acids in these tissues. The results confirm the value of a good quality protein supplement or more targeted supply of rumen-protected intestinally-available methionine to correct a frequently apparent deficiency in sulphur amino acid supply for (a) growth of hair fibre by Angora goats and, less consistently, by Cashmere goats and (b) other body tissues in both genotypes.