Comparison of the ileal digestibility of amino acids in ground barley for the growing rat and pig

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Abstract
The apparent and true ileal digestibility of amino acids in ground barley were compared in growing rats (n = 12) and pigs (n = 11) after sampling ileal contents in both species at slaughter. The animals were given a diet containing ground barley as the sole protein source at 6 levels of intake. Regression analysis was used to determine the endogenous flow of amino acids at the terminal ileum. There was no consistent effect of feeding level on the apparent digestibility of amino acids in either species. There were no significant differences (P > 0.05) between the rat and pig for the apparent digestibility of threonine, valine, isoleucine, leucine, tyrosine, and lysine. There were significant (P < 0.05) differences between species, however, for methionine, phenylalanine, and most of the non-essential amino acids. The apparent ileal digestibility of amino acids in ground barley ranged from 0.37 for glycine to 0.90 for arginine in the rat and from 0.63 for glycine to 0.86 for glutamic acid in the pig. Measurements of true amino acid digestibility were less variable in the rat than in the pig. For the pig, the low correlation between ileal amino acid flow and amino acid intake prevented accurate determination of endogenous amino acid flow and therefore reduced the meaningfulness of the species comparison of true digestibility. The mean difference between the rat and pig for the apparent digestibility of amino acids was 0.08, whereas the mean difference in true digestibility was 0.05. Consideration of these and previously unpublished comparisons indicated agreement between the rat and pig for the apparent ileal digestibility of all the essential amino acids in barley (excepting methionine).