Digestion in the pigs between 7 and 35 d of age. 4. The digestion of amino acids in pigs given milk and soya-bean proteins.

1. In two experiments, forty-four pigs weaned at 4--5 d of age were given diets containing milk or soya-bean proteins until slaughtered at 14, 28, or 35 d of age. 2. Additions of methionine and methionine plus lysine to the diets did not increase the proportions of these amino acids in ileal digesta. 3. In the pigs given a nitrogen-free diet, ileal digesta contained more threonine, proline and glycine than in pigs given diets containing protein. 4. The apparent and true digestibility of amino acids were greater when milk protein was fed than when soya-bean proteins were fed. 5. The apparent digestion of amino acids to the ileum of pigs given isolated soya-bean protein (ISP; Supro 610) increased with increasing age of pigs from a mean of 0 . 82 at 14 d of age to 0 . 87 at 35 d of age. 6. When milk protein was fed apparent digestibilities of methionine and lysine to the ileum were 0 . 912 and 0 . 905. The apparent digestibility of threonine to the ileum was 0 . 800, 0 . 774 and 0 . 504 for pigs given the milk-, ISP and soya-bean-meal (SBM)-protein diets respectively. 7. Apparent digestibilities of total essential and non-essential amino acids were 0 . 79 and 0 . 69 respectively, and true digestibilities of both were 0 . 82.