Factors affecting efficacy of methionine hydroxy analogue for chicks fed amino acid diets.

Chicks were fed mixtures of methionine, cystine, and the calcium salt of the hydroxy analogue of methionine (MHA) in a diet based on a mixture of amino acids. Rate of gain with the basic amino acid diet containing a mixture of methionine and cystine was about 90% of the rate noted with a practical type diet. Efficacy of MHA depended on its level in the diet and on the levels of methionine and cystine fed with it. It was least effective when fed as the only sulfur amino acid or when fed with cystine. When fed with methionine it had intermediate value and was most efficacious when fed with a mixture of methionine and cystine. Essentially it was fully effective when it provided 25% of the sulfur amino acids with the remainder as equal parts of methionine and cystine. Replacing part of the cystine in a mixture of cystine and MHA with methionine resulted in a marked improvement in performance with L-methionine being slightly more effective than D-methionine.