Effects of ileal endogenous nitrogen losses and dietary amino acid supplementation on nitrogen retention in growing pigs

The relationship between ileal endogenous nitrogen (N) losses and N retenti on was studied in two experiments with growing pigs of 40 to 60 kg. In Expe riment 1, 13 ileal cannulated castrated males were fed diets based on maize starch, containing either soyabean meal (SBM) with a low trypsin inhibitor activity (TIA), a mixture of toasted and untoasted soyabean meal with a hi gh TIA (mSBM), a commercial batch of peas, or rapeseed expeller cake (RC). Ileal endogenous N recovery was measured using the N-15-isotope dilution te chnique. Apparent ileal digestibility of crude protein (CP) for the SBM, mS BM, pea and RC diets were 82.8, 72.0, 76.7 and 68.7% (P < 0.05). True ileal CP digestibility for the diets was 96.5, 93.0, 94.0 and 87.5% (P < 0.05), and the recovery of ileal endogenous N was 3.08, 6.01, 4.55 and 5.36 g/kg D MI (P < 0.05). In Experiment 2, sixteen castrated males were used to determ ine N retention, using almost similar diets as in Experiment 1. The diets c ontained either SBM, mSBM or peas and were balanced for the contents of app arent ileal digestible (ID) CP (96 g/kg) and ID essential amino acids (EAA; at least 85% of requirement values). The fourth treatment was a diet with mSBM as protein source, but supplemented with EAA to the level of 95% of th e requirement values (diet mSBMs). Apparent faecal CP digestibility for the SBM, mSBM, pea and mSBMs diets was 88.6, 87.2, 86.1 and 86.0% (P < 0.05). Urinary N excretion and N retention for these treatments were 0.39, 0.59, 0 .40, 0.53 (P < 0.05) and 0.87, 0.80, 0.85, 0.84 g/kg(0.75)/day (P < 0.05), respectively. Utilization of dietary ID N for N retention were 79.8, 73.3, 78.2 and 77.6% (P < 0.05), respectively. The study showed that increased il eal endogenous N losses are associated with higher losses of urinary N and with a lower N retention. Supplementation of extra essential AA to a diet c ausing a relatively high flow of ileal endogenous N, may compensate for the lower N utilization under these conditions, and thus limit effects on N re tention. (C) 1999 Elsevier Science B.V. All rights reserved.