THE ILEAL DIGESTIBILITY OF NITROGEN AND AMINO-ACIDS IN MEAT AND BONE MEALS DETERMINED USING A RAT ASSAY

The proximate and gross amino acid compositions of meat and bone meals from three rendering plants sampled five times throughout the killing season and from one plant sampled on four occasions, were determined. Apparent and true ileal nitrogen and amino acid digestibilities were determined using a rat assay on three of the samples from each plant. There was considerable between- and within-plant variation for most of the chemical components, in particular the amino acids. Mean apparent ileal nitrogen digestibility of the 12 samples was 0.64 with a range of 0.54-0.75. Ileal apparent amino acid digestibilities of the meals, with a few exceptions, showed a similar pattern to nitrogen digestibility. Regression equations derived for the prediction of apparent ileal amino acid digestibilities from apparent ileal nitrogen digestibility had residual standard errors of 0.04-0.10. Endogenous ileal nitrogen and amino acid excretions were determined following protein-free alimentation. The resultant overall mean differences between true and apparent ileal amino acid digestibility ranged from 0.019 (arginine) to 0.094 (threonine) and that for nitrogen digestibility was 0.046. The variable ileal digestible amino acid content of meat and bone meals emphasises the limitation of tabulated analytical values and the need for a routine relatively inexpensive assay if the meals are to be used efficiently as protein supplements in diet formulation.