Variability of apparent ileal amino acid digestibility in high-protein wheat samples for growing-finishing pigs

An experiment was conducted to investigate factors responsible for the variability of apparent ileal digestibility values of amino acids (AA) in high-protein wheat samples. Six barrows, average initial body weight 30.5 kg, fitted with a simple T-cannula at the distal ileum, were fed six diets according to a 6 x 6 Latin square design. The six diets included 970 g kg(-1) of different samples of wheat. Chromic oxide was used as the digestibility marker. The barrows were fed twice daily, at 08:00 and 20:00 h. The dietary allowance was 1,600 g d(-1). Each experimental period consisted of 8 d. Ileal digesta were collected for a total of 24 h, at 2-h intervals, from 08:00 on d 6 Id 08:00 h on d 8. There were differences (P <0.05) in the apparent ileal digestibility values of all amino acids (AA) among the wheat samples. Of the indispensable (+semi-) amino acids (AA), within each sample, the digestibility values of lysine and threonine, the first- and second-limiting AA, were lowest and ranged from 59.0 to 70.3 (P <0.05) and 64.2 to 73.0% (P <0.05), respectively. With the exception of arginine and tyrosine, the digestibility values of the other indispensable (+semi-) AA, were negatively correlated (P <0.05) with neutral-detergent fibre (NDF) content, whereas differences in dietary AA contents did not affect the variability of the ileal AA digestibility values in the wheat samples. In conclusion, measured with the ileal analysis method, there was considerable variation in the digestibility values of AA in high-protein wheat samples. Differences in NDF content were, in part, responsible for the variation. Furthermore, the relatively low digestibility values of lysine, threonine and tryptophan further accentuate the limitation of these AA in proteins from wheat.