DETERMINATION OF APPARENT ILEAL AMINO-ACID DIGESTIBILITY IN PEAS FOR PIGS WITH THE DIRECT, DIFFERENCE AND REGRESSION METHODS

Three methods were evaluated for the determination of apparent ileal digestibility values of amino acids in peas (242 g crude protein/kg peas, as-fed basis). Five barrows, average initial body weight 34.6 kg, were fitted with a simple T-cannula at the distal ileum and fed five diets according to a 5X5 Latin square design. Diet 1 contained 885 g wheat/kg providing the sole source of dietary amino acids. Diets 2, 3 and 4 contained three graded levels of peas (168, 336 and 504 g/kg diet, respectively) and wheat (664, 443 and 221 g/kg diet, respectively). Diet 5 contained 671 g peas/kg diet, which provided the sole source of dietary amino acids. All the diets were formulated to contain 160 g crude protein/kg (as-fed basis). Chromic oxide (4 g/kg diet) was included as the digestibility marker. Each experimental period comprised 8 d. The pigs were fed twice daily, equal amounts, at 08:00 and 20:00 h. The dietary allowance was 1800 g/d. Ileal digesta were collected for a total of 24 h, at 2-h intervals, during d 7 and 9. Apparent ileal digestibility values of amino acids in peas were determined with the direct method from diet 5, with the difference method from diets 2, 3 and 4 and with the regression method from diets 2, 3, 4 and 5, respectively. The accuracy of the determination of apparent ileal amino acid digestibility values in peas with the difference method was dependent on the level of inclusion of the peas in the assay diet, as reflected by differences in the standard errors of the digestibility values. There were no differences (P>0.05) in the digestibility values of peas when these were determined with the direct, difference and regression methods. These results show that the apparent ileal digestibility values of amino acids in feedstuffs with a medium-protein content, such as peas, can be determined with either method, including the difference method when the inclusion level of the assay feedstuff is relatively high.