Variability of apparent ileal amino acid digestibility in canola meal for growing-finishing pigs

Studies were conducted with six barrows, average initial body weight 32.5 kg, fitted with a T-cannula at the distal ileum, to determine some of the factors responsible for the variability in apparent ileal digestibility values of amino acids (AA) in canola meal. The barrows were fed six corn starch-based diets, formulated to contain 18.0% crude protein (CP) on a dry matter (DM) basis from six canola meal samples, according to a 6 x 6 Latin square design. Chromic oxide (0.3%) was used as a digestibility marker. The pigs were fed twice daily, at 08:00 and 20:00 h. The dietary allowance was 1600 g d(-1). Each experimental period consisted of 8 d. Ileal digesta were collected, at 2-h intervals, for a total of 24 h from 08:00 on day 6 to 08:00 h on day 8. With the exception of proline, there were differences (P < 0.05) in the apparent ileal digestibility values of all AA among the six canola meal samples. Of the indispensable AA in canola meal, the digestibility values of arginine, histidine, and methionine were relatively high, ranging from 79.4 to 84.4, from 76.5 to 81.0%, and from 77.3 to 82.4%, respectively, while the digestibility values of threonine and tryptophan were relatively low, ranging from 59.7 to 66.5 and from 61.7 to 67.5%, respectively. Furthermore, with the exception of arginine, the digestibility values of the indispensable PLA were negatively correlated (P < 0.05) with the neutral-detergent fiber (NDF) content in canola meal. In addition, with the exception of threonine, tryptophan and valine, the digestibility values of the indispensable AA were positively correlated (P < 0.05) with their respective dietary levels. In conclusion, measured with the ileal analysis method, there were differences (P < 0.05) in the digestibility values of the majority of AA among the canola meal samples. Differences in NDF content were mainly responsible for the variation. In addition, differences in the dietary levels of most AA also contributed, in part, to the variation of AA digestibility values.