Blood serum and tissue free amino acid concentrations of gilts fed DL- or L-methionine

A semipurified ration containing 0.55% DL-methionine was fed to two gilts from each of two litters, and 0.55% L-methionine was fed to an additional two gilts from each litter. Duodenal, liver, and serum methionine levels were higher when DL-methionine was fed, indicating differences in the abilities of the test gilts to utilize the D- and L-isomers. Serum and muscle methionine levels were higher for litter 2, suggesting possible methionine requirement differences between the two litters. Histidine, isoleucine, and leucine appeared to accumulate in muscle, serum, and liver, respectively, suggesting some form of short-term storage. The accumulation of histidine in muscle tissue was thought to partially explain the fluctuations often associated with serum histidine levels that have not been explainable in terms of diet. A need for further research into factors affecting amino acid requirements was indicated.