Total Sulfur—Containing Amino Acids Isoleucine and Tryptophan Requirements of the Finishing Pig for Maximum Nitrogen Retention

Four finishing pigs were employed in each of three 4 × 4 latin square designs to study the total sulfur-bearing amino acids, isoleucine and tryptophan requirements. In the total sulfur-bearing amino acids and isoleucine studies graded levels of the test amino acid were added to a 14.1% protein basal diet (protein from corn and gelatin) containing 3,700 kcal metabilizable energy per kilogram. In the tryptophan study the diet contained 13.6% protein and 3,727 kcal metabolizable energy per kilogram. In all studies essential amino acids, excepting the given test amino acids, were provided in concentrations of 1.2 times the published requirements. In each 4 × 4 latin square design four barrows, four dietary treatments and four 10-day periods were employed. There were no significant differences in nitrogen retention among the four periods. Amino acid requirements were determined by the method of least squares. Addition of methionine to a basal diet containing .17% total sulfur-bearing amino acids did not significantly increase nitrogen retention. Expressed as a percent of the diet, estimated requirements for isoleucine and tryptophan were, respectively, .31 ± .01% and .059 ± .001%.