1. Large White x Landrace pigs were used to study the effects of supplementation with limiting amino acids of diets based on wheat containing 13% crude protein. Measurements were made of growth rate, feed conversion, carcass composition, plasma-free amino acid concentrations, digestibility of dry matter, nitrogen and gross energy, nitrogen retention and metabolizable energy.
2. A wheat diet supplemented with lysine and threonine, the firstand the second-limiting amino acids respectively, produced almost the same growth rate and feed conversion ratio as one supplemented with fish meal and meat meal. Methionine was probably the thirdlimiting amino acid, and additional supplementation with methionine produced a further small improvement in growth rate and feed conversion ratio to the point where they were equal to those on the diet supplemented with fish meal and meat meal.
3. Supplementation of the wheat diet with lysine only produced the same growth rate and feed conversion ratio as a least-cost commercial diet; performance was, however, inferior to that on a wheat diet supplemented with fish meal and meat meal. The commercial diet had a lower dry-matter digestibility.
4. Eye-muscle area of pigs on the wheat diet supplemented with lysine was similar to that of pigs on a wheat diet supplemented with fish meal and meat meal; however, backfat thickness was significantly lower on the latter diet.
5. Except for threonine, plasma-free amino acid concentrations reflected with reasonable accuracy amino acid deficiencies in the diets.