Effects of the infusion of amino acids into the abomasum of sheep, with emphasis on the relative value of methionine, cysteine and homocysteine for wool growth

Abstract

SUMMARYMerino sheep were given abomasal infusions of various amino acids or mixtures of amino acids. Effects on wool growth were measured using autoradiography or a clipping procedure and changes in the concentration of amino acids in plasma were measured in some experiments.Mixtures of five (28 g/day) or ten (45 g/day) essential amino acids (both mixtures containing 3 g methionine) stimulated wool growth of sheep receiving a maintenance ration; on average, the volume of wool grown increased 48% and 86%, respectively. When cysteine completely replaced methionine in these mixtures, wool growth was markedly reduced, but two-thirds of the methionine could be replaced by cysteine without affecting wool growth. Homocysteine was partially effective in replacing methionine and, when supplemented with betaine, folic acid and vitamin B12, the mixture was still significantly inferior to that containing methionine. In contrast, abomasal supplements of methionine or homocysteine alone were equivalent as supplements for wool growth. The results indicated a specific role for methionine in the control of wool growth, other than the provision of cysteine. This role was postulated to be related to some function of S-adenosylmethionine.Infusion often essential amino acids caused appreciable increases in the concentrations of cystine, methionine, cystathionine and taurine in plasma; total essential amino acids increased threefold whereas nonessential amino acids decreased in concentration. The replacement of methionine in the infusion by cysteine or homocysteine significantly altered the concentration of cystine, methionine and cystathionine in plasma.Evidence was obtained that the adverse effects on wool growth of high abomasal doses of methionine (10g/day) could not be reduced or prevented by provision of additional glycine and were not related to the supposed toxic effects of 3-methylthiopropionic acid, a metabolite of the transamination pathway.

Expression of bacterial cysteine biosynthesis genes in transgenic mice and sheep: toward a newin vivo amino acid biosynthesis pathway and improved wool growth

“…0962-8819 9 1995 Chapman & Hall methionine or cysteine either directly into the bloodstream or into the abomasum (the glandular compartment of the ruminant stomach) of Merino sheep at a rate of 1.0-3.0 g per sheep per day leads to an increase in the rate of mitosis (Hynd, 1989) and wool growth Schinckel, 1963, 1964;Reis et al, 1990). A similar effect upon mohair yield in Angora goats has been observed following infusion of methionine at a rate of 1.0 g per goat per day (Sahlu and Fernandez, 1992).…”

Promotion of cashmere growth by sulfur supplements in cashmere goats

“…Sulfur amino acids are mostly in the form of cystine in wool fibres, but there are only small amounts of cysteine and methionine (Reis & Schinkel, 1963;Reis, 1967;McGuirk, 1983;Reis et al, 1990), and a large amount of cysteine is required for cystine synthesis. Most cystine and cysteine in sheep and goats are absorbed from the gastro-intestinal tract, but the others are transformed by methionine through the trans-sulfuration pathway (Reis, 1989).…”

Fractional protein synthesis rate and polyamine concentrations in tissues of Merino sheep selected for gastrointestinal nematode resistance

“…It has been proved that oxidation of methionine occurs in the gastrointestinal tract of sheep, accounting for a 9% of whole-body methionine oxidation (Lobley et al, 2003). As methionine and cysteine are limiting amino acids in wool-producing sheep (Reis et al, 1990), the change of methionine oxidation in the gastrointestinal tract in response to nematode infection would have a significant influence on the status of nutrition and the immunity of the host and warrants further experimental research.…”