Methionine requirement of the growing kitten, in the absence of dietary cystine

This study was conducted to determine the methionine requirement for maximal weight gain and nitrogen retention in growing kittens fed a 24% crystalline amino acid diet containing no cystine. Six male and six female kittens were fed each of six levels of methionine, 0.45, 0.7, 0.8, 0.9, 1.0 and 1.5% of the diet, for 10 days in a 6 X 6 Latin square design. Diets were made isonitrogenous with alanine and were isocaloric with a calculated metabolizable energy of approximately 5.0 kcal/g, Food intake and body weight were recorded daily, and nitrogen balance for each cat in each 10-day period was determined. On the 7th day of each period, blood was drawn for subsequent analysis of plasma methionine concentrations. From growth response results, the methionine requirement in the absence of dietary cystine was estimated to be 0.70% of the diet for male and female kittens. On the basis of nitrogen balance results, the methionine requirement appeared to be slightly higher, at 0.75% of the diet for both sexes. Plasma methionine concentrations appear to increase exponentially with dietary methionine concentrations, and were of limited usefulness in estimating the methionine requirement of the kitten in the context of the experimental protocol used here.