ESTIMATING ENDOGENOUS AMINO-ACID FLOWS AT THE TERMINAL ILEUM AND TRUEILEAL AMINO-ACID DIGESTIBILITIES IN FEEDSTUFFS FOR GROWING PIGS USINGTHE HOMOARGININE METHOD

True ileal lysine digestibilities were determined using the homoargini ne (HA) method in casein-, barley-, canola meal-, and barley-canola me al-based diets fed to growing pigs. Four Yorkshire barrows (25 to 49 k g BW) equipped with ileal T-cannulas were fed one of the diets accordi ng to a 4 x 4 Latin square design. All diets, except for the barley di et, were formulated to be similar in DE:CP ratio. Ileal digesta were c ollected continuously for 24 h on d 7 and 9 of each experimental perio d for determining apparent and true ileal digestibilities, respectivel y. True ileal lysine digestibility and endogenous flows were determine d by feeding diets in which 50% of the protein-containing ingredients, was guanidinated; the conversion of lysine to HA allows for direct de termination of true lysine digestibilities. The apparent ileal CP and amino acid digestibilities were higher (P < .05) in the casein diet th an in the barley, canola meal, and barley-canola meal diets. The CP di gestibility was higher(P <.05) in the barley-canola meal diet than in the barley and canola meal diets. Endogenous lysine losses were influe nced 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 digestib ilities seemed additive in the barley-canola meal mixture.