Evaluation of the reference diet substitution method for determination of apparent nutrient digestibility coefficients of feed ingredients for South African abalone ( Haliotis midae L.)

Abstract

Apparent nutrient (dry matter, organic matter, energy, protein) digestibility of sunflower meal, canola meal and peanut meal, substituted at 20% inclusion level into a reference diet, was determined for Haliotis midae in this study. In a second experiment, the influence of inclusion level of a feed ingredient (soybean meal) on apparent dry matter, organic matter, energy and protein digestibility was evaluated. Apparent protein digestibility coefficients exceeding 100% were found for sunflower meal and canola meal included into a reference diet. This also occurred when evaluating different inclusion levels of soybean meal into a fish meal reference diet, eliminating the opportunity to test the influence of inclusion level of soybean meal on apparent nutrient digestibility. Associative effects between different feed ingredients, diet and faecal nutrient leaching and mathematical artifacts in calculations when using substitution vs. single protein diets might have an influence on final apparent digestibility coefficients (ADCs) of highly digestible feed ingredients. It was found that apparent protein digestibility coefficients determined with single protein diets predicted determined digestibility in compound diets with an error of less than 3.3% compared to a deviation of 13% to 16% when using coefficients determined with substitution trials. The conclusion from this study is that single protein diets should be used for determining apparent protein digestibility coefficients of feed ingredients for H. midae when evaluating feed ingredients for feed composition tables.