Assessment of the True Ileal Digestibility of Reactive Lysine as a Predictor of Lysine Uptake from the Small Intestine of the Growing Pig

The aim of this study was to evaluate the accuracy of a newly developed assay for determining digestible reactive lysine in processed protein sources. Pigs were fed either a heated skim milk powder based diet or one of two control diets in which the sole source of nitrogen was a mixture of enzymatically hydrolyzed casein (EHC) and synthetic amino acids. One control diet (EHC diet A) was formulated to contain the same amount of digestible lysine (determined using a conventional true ileal amino acid digestibility assay) while the other (EHC diet B) was formulated to contain the same amount of digestible reactive lysine (determined using the new assay) present in the test diet. Lysine was the first limiting amino acid in all three diets. The whole body lysine deposition and empty body weight gain of pigs fed the heated skim milk powder diet were not significantly different from those of pigs fed EHC diet B but were significantly higher than those of animals fed EHC diet A. This experiment demonstrates that the new assay for determining digestible reactive lysine could be more accurate when applied to this heated protein source than the conventional true ileal amino acid digestibility assay.