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Abstract A study was conducted to determine the effects of different fiber and lipid sources on the digestibility of amino acids (AA) in growing pigs. Five diets were fed in this study. The diets were corn-soybean meal-based diet with either soybean hulls (SBH) or sugar beet pulp (SBP) as fiber source and either soybean oil (SBO) or choice white grease (CWG) as lipid source in a 2 × 2 factorial arrangement; and a N-free diet. The diets were formulated to be similar in content of AA, calcium, available phosphorus, and total dietary fiber. The SBH and SBP were each included in their respective diets at 15%, whereas the SBO and CWG were each included in their respective diets at 4.5%. The 5 diets were fed to 10 ileal-cannulated pigs 5 barrows and 5 gilts; initial average body weight (BW) = 54.8 ± 5.6 kg)in a 5 × 5 Latin square design to give 10 replicates per diet. On an as fed basis, SBH and SBP contained 11.3 and 8.8% crude protein, 66.1 and 49.8% total non-starch-polysaccharides (NSP), 54.3 and 29.5% insoluble NSP, and 11.8 and 20.3% soluble NSP, respectively. The SBO and CWG contained 98.5 and 98.5% crude fat, 14.7 and 35.6% saturated fatty acids, and 76.6 and 62.5% unsaturated fatty acids, respectively. Dietary fiber source and lipid sources did not interact on standardized ileal digestibility (SID) of AA. The SBH- and SBP-containing diets did not differ regarding SID of all AA except Met and Trp. Pigs fed SBP-containing diets had lower (P 0.05) SID of Met and greater (P 0.05) SID of Trp than those fed SBH-containing diets by 2.5 and 4.7%, respectively. The SBO- and CWG-containing diets did not differ regarding SID of all AA except Trp. The SID of Trp for SBO-containing diets was greater (P 0.05) than that for CWG-containing diets by 2.6%. In conclusion, the lack of interaction between dietary fiber and lipid sources on the SID of AA implies that these two factors (fiber and lipid sources) may exert their effects on ileal digestibility of AA independently if the fiber and lipid sources are included in diets for growing pigs at same levels included in the diets fed in the current study. The dietary fiber source and dietary lipid source had limited effects on the digestibility of most AA, implying that replacement of one fiber source with one another fiber source or of one lipid source with another lipid source in diets for growing pigs may have limited effect on digestibility of AA if the fiber and lipid sources are included in diets for growing pigs at same levels included in the diets fed in the current study.
Hong et al. (Sun,) studied this question.