Assessment of apparent ileal lysine digestibility for use in diet formulation for the growing pig

Abstract

The apparent ileal digestibility of lysine in a balanced diet comprising barley, meat and bone meal, fish meal and pollard as its protein sources, was determined with six growing pigs, using the slaughter technique. The mean apparent digestibility of lysine was 0.59. Concurrent with the digestibility study, a pig growth trial was conducted to determine the accuracy of ileal digestible lysine intake as a predictor of pig performance. Fifteen intact male pigs were allocated to five casein-based diets and eight pigs were allocated to the barley-based diet used in the ability study. Lysine was confirmed as the first-limiting amino acid in all diets and minerals, vitamins and essential fatty acids were in excess of requirements. The nitrogen source of the casein-based diets was lactic casein and synthetic amino acids and they had different gross lysine to digestible energy ratios. The 23 pigs were given fixed levels of meal over a 49 day period such that all received equal intakes of digestible energy. The pigs were then slaughtered and the total lysine contents of their carcasses were determined. Linear regressions of mean daily body weight gain and carcass lysine content against daily amounts of absorbed lysine were determined for the casein-fed pigs, with the assumption that the dietary lysine was completely absorbed. The actual performance of pigs on the barley-based diet was compared with that predicted using the regression equations, based on the determined (digestibility study) levels of barley-diet lysine absorbed daily. Predicted and mean actual (± SE) growth rates for the barley-fed pigs were 550 g day −1 and 509 (± 30.24) g day −1, respectively, while predicted and mean actual (± SE) carcass lysine contents were 403 g and 325 (± 25.5) g, respectively. The estimates of apparent ileal lysine digestibility overestimated the degree of lysine availability and may have overestimated the degree of lysine uptake from the gut.