Ileal digestibility of amino acids in feed ingredients for 22-, 56-, and 87-kg pigs

The objective of this experiment was to test the hypothesis that the apparent ileal digestibility (AID) of amino acids (AA) in feed ingredients is not constant in pigs with 3 different body weights (BW) after reaching 20 kg. Eight ileal-cannulated pigs with an initial BW of 22.2 kg (standard deviation = 1.2) were used in a 2-period cross-over design. Each period consisted of a 5-d adaptation and a 2-d ileal digesta collection. Two experimental diets contained corn distiller's dried grains with solubles (DDGS) or a soybean meal-wheat mixture (SWM; 70% soybean meal + 30% wheat) as the sole source of nitrogen, respectively. The same pigs were used for the heavier BW groups. The diets and experimental procedure for 55.6 kg (standard deviation = 3.3) pigs and 86.9 kg (standard deviation = 5.1) pigs were identical to those used for 22.2 kg pigs. The AID values were calculated using the index method, with chromic oxide as the indigestible index. A linear increase in the AID of most AA with increasing BW of pigs was observed only in the SWM, whereas no significant difference was observed in the AID of most AA among the different BW groups in corn DDGS (interaction; P < 0.05). The linear increase in the AID values in the SWM is primarily because of the increase from 22 to 56 kg rather than 56 to 87 kg. In conclusion, the AID values of most AA in the SWM were not constant across the BW range of 22 to 87 kg, whereas corn DDGS did not show such variation.