Ileal apparent protein and amino acid digestibilities and endogenous nitrogen losses in pigs fed soybean and rapeseed products.

We investigated the effects of various protein sources on the apparent ileal digestibilities (AID) of CP and amino acids (AA) and on the recoveries of ileal endogenous nitrogen (N) in pigs. Ileal endogenous N losses (ENL) were measured using the 15N-isotope dilution method. Thirteen pigs (BW of 13 to 20 kg) were fitted with a post-valve-T-cecal cannula and two indwelling blood catheters. They were fed twice daily at a level of 2.6 times ME for maintenance. Cornstarch-based diets contained a soy concentrate (SC; 180.5 g/kg), soybean meal (SBM; 295 g/kg), or a mixture of toasted and untoasted soybean meal (mSBM; 330.4 g/kg) in Trial I or three rapeseed cakes, dehulled-toasted (RC1; 395 g/kg), non-dehulled-toasted (RC2; 458 g/kg), and dehulled-untoasted (RC3; 390 g/kg) in Trial II. The protein sources provided diets with similar levels of apparent ileal digestible CP (108 g/kg as-fed diet) and Lys, Met+Cys, Thr, and Trp. The AID of CP was greater (P < .05) for the SC (86.8%) and SBM (82.8%) than for the SBM (68.1%) diet. In Trial II, the AID of CP was greater (P < .05) for RC1 (76.2%) and RC3 (75.8%) than for the RC2 (69.5%) diet. For all diets, the differences in the AID for most of the AA corresponded to the differences in the AID of CP. The ENL (g/kg DMI) were greater (P < .05) for the mSBM diet (3.75) than for the SC (2.53) and SBM (2.53) diets in Trial I but were similar (P > .05; 2.24, 3.03, and 2.89 for RC1, RC2, and RC3, respectively) among diets in Trial II. We concluded that AID of CP of the soybean diets were associated with endogenous and dietary N losses. For these diets, increased ENL and dietary N losses were associated with a higher dietary trypsin inhibitor activity. For the rapeseed diets, dehulling increased AID of CP and AA, due to reduced ENL (P = .08) and dietary N losses (P < .05). Toasting of dehulled rapeseed cake did not affect the AID of CP and AA (P > .05) while reducing the true ileal CP digestibility (P < .05).