Determination of additivity of apparent and standard ileal digestibility of amino acids in different ingredients for mixed diets fed to growing pigs

Abstract Text: An experiment was conducted in growing pigs to investigate the additivity of apparent (AID) or standardized (SID) ileal digestibility of CP and AA in mixed diets based on multiple protein sources. Additivity refers to values calculated (predicted) from determined AID or SID of individual ingredients versus measured values in mixed diets. Using the measured AID or SID for CP and AA in corn, soybean meal (SBM), corn distillers’ dried grains with solubles (DDGS), or canola meal (CM), the AID or SID for 4 mixed diets based on corn-SBM (CS, 65% corn and 22% SBM), corn-SBM-DDGS (CSD, 57% corn, 17% SBM, and 11% DDGS), corn-SBM-CM (CSCM, 58% corn, 13% SBM, and 13% CM), or corn-SBM-DDGS-CM (CSDCM, 55% corn, 10% SBM, 10% DDGS, and 10% CM) were predicted and compared with measured AID or SID, respectively. T-test was applied to test the difference between predicted and measured values. Eighteen pigs (initial BW = 61.3 ± 5.5 kg) were surgically fitted with T-cannula and assigned to a duplicated 9 × 4 incomplete Latin square design with 9 diets and 4 periods. The experimental diets consisted of 4 semi-purified diets to determine the AID and SID in the 4 ingredients, 4 mixed diets, and a nitrogen-free diet. Chromic oxide was added as an indigestible marker. Pigs were fed one of the diets during each 7-d period, and the ileal digesta were collected on d 6 and 7, from 0800 to 1800. The results showed the predicted SID were consistent with determined values, except for Leu, Thr, Asp, Cys, Pro, and Ser, in CS diet; Met and Cys in CSD diet. The determined AID for total AA and 5 individual AA (Arg, His, Trp, Gly, and Pro) in CS diet were greater (P < 0.05) than predicted. For CSD diet, the determined AID were greater (P < 0.05) than predicted for CP, total AA, and all AA except for Arg, Leu, and Pro. In CSCM diet, the determined AID were greater (P < 0.05) than predicted for 3 AA (Arg, Cys, and Gly). When compared with determined values, predicted AID in CSDCM diet were lower (P< 0.05) for total AA and 4 AA (Arg, Met, Cys, and Pro). In conclusion, the results indicate that SID of AA are more consistent than AID for predicting ileal digestibility of AA in mixed diets containing multiple protein sources.

Keywords: additivity, amino acid, ileal digestibility