Sulfur amino acid requirements of immature Beagle dogs.

The methionine and total sulfur amino acid requirements of growing Beagle dogs were determined using diets containing purified L-amino acids as the sole nitrogen source. In the presence of 0.60% dietary L-cystine, optimal growth, feed efficiency, and nitrogen retention were attained in dogs fed diets containing 0.20% or more L-methionine. Two additional experiments revealed that maximal growth, feed efficiency, and nitrogen retention occurred in growing dogs fed diets containing 0.20% L-methionine and supplemented with 0.15% or more L-cystine. Therefore, the total sulfur amino acid requirement was estimated to be 0.39% methionine. Cystine, on an isosulfurous basis could effectively supply up to approximately 50% of the total sulfur amino acid requirement. In crystalline amino acid diets, D-methionine, DL-methionine, N-acetyl-L-methionine and methionine hydroxy analogue were effective in replacing the L-methionine requirement of growing Beagles. N-acetyl-D-methionine, however, was not efficiently utilized as a substitute for dietary methionine.