Methionine and cystine requirements of growing turkeys

Sulfur amino acid requirements of starting, growing, finishing male Large White turkeys were investigated in three experiments using 3000 turkeys. Requirements were determined by least squares analyses of response curves obtained by supplementing methionine and cystine deficient basal diets with graded levels of DL-methionine and/or L-cystine. Experiments were conducted from 1 to 4, 8 to 12, and 16 to 20 weeks of age. Diets included starch, soybean meal, faba beans, and field peas. Requirements for total sulfur amino acids (TSAA) determined with diets marginally deficient in cystine were .95 to 1.01, .70 to .71, and .43 to .48% of the diet for starting (1 to 4 weeks), growing (8 to 12 weeks), finishing (16 to 20 weeks) turkeys, respectively, in different experiments. On the basis of dietary metabolizable energy, the respective TSAA requirement values (in %/therm) were .298 to .332, .205 to .221, and .128 to .134. Minimum methionine requirements (determined with excess dietary cystine) were .46, .30, and .19% of the diet for starting, growing, and finishing turkeys, respectively. Cystine replacement values, calculated by dividing the maximum usable levels of cystine (TSAA requirements minus methionine requirements) by TSAA requirements were 55, 58, and 57% of the TSAA requirement for starting, growing, and finishing turkeys, respectively.