Utilization of ileal digestible amino acids by growing pigs: methionine.

An experiment was conducted to determine the utilization of ileal digestible methionine by growing pigs. Three methionine-deficient diets (0.09 g ileal digestible methionine/MJ digestible energy (DE)) were formulated using cottonseed meal, meat-and-bone meal and soya-bean meal respectively as the only source of methionine in the diet. An additional three diets were formulated with supplements of methionine to confirm that methionine was limiting in the first three diets. The growth performance and retention of methionine by pigs given the six diets over the 20-45 kg growth phase was then determined. Growth rates (g/d) of pigs given the three diets formulated to 0.09 g ileal digestible methionine/MJ DE were significantly different (P < 0.01): cottonseed meal 411, meat-and-bone meal 442, soya-bean meal 496 (SED 24.6). The response of pigs to the addition of methionine confirmed that methionine was limiting in these diets. Crude protein (N x 6.25) deposited by the pigs (g/d) was significantly higher (P < 0.05) for those given soya-bean meal (61) and meat-and-bone meal (57) relative to cottonseed meal (47; SED 3.3). The proportion of ileal digestible methionine retained by pigs given the three protein concentrates was: cottonseed meal 0.39, meat-and-bone meal 0.45, soya-bean meal 0.47 (SED 0.019). These results indicate that values for the ileal digestibility of methionine in protein concentrates do not reflect the proportion of methionine that can be utilized by the pig. It appears that, with heat-processed meals, a considerable proportion of the methionine is absorbed in a form(s) that is (are) inefficiently utilized.