Estimating endogenous amino acid flows at the terminal ileum and true ileal amino acid digestibilities in feedstuffs for growing pigs using the homoarginine method.

True ileal lysine digestibilities were determined using the homoarginine (HA) method in casein-, barley-, canola meal-, and barley-canola meal-based diets fed to growing pigs. Four Yorkshire barrows (25 to 49 kg BW) equipped with ileal T-cannulas were fed one of the diets according to a 4 x 4 Latin square design. All diets, except for the barley diet, were formulated to be similar in DE:CP ratio. Ileal digesta were collected continuously for 24 h on d 7 and 9 of each experimental period for determining apparent and true ileal digestibilities, respectively. True ileal lysine digestibility and endogenous flows were determined by feeding diets in which 50% of the protein-containing ingredients was guanidinated; the conversion of lysine to HA allows for direct determination of true lysine digestibilities. The apparent ileal CP and amino acid digestibilities were higher (P < .05) in the casein diet than in the barley, canola meal, and barley-canola meal diets. The CP digestibility was higher (P < .05) in the barley-canola meal diet than in the barley and canola meal diets. Endogenous lysine losses were influenced by diet (P < .05) and ranged between 586 and 1,429 mg/kg DM intake. True ileal lysine digestibilities in barley, canola meal, and barley-canola meal diets were similar (P > .05) and lower (P < .05) than in the casein diet. The true ileal amino acid digestibilities were estimated for other amino acids. Unlike apparent digestibilities, true digestibilities seemed additive in the barley-canola meal mixture.