TRUE ILEAL DIGESTIBILITY OF AMINO-ACIDS IN MEAT AND BONE MEAL FOR THE GROWING PIG - APPLICATION OF A ROUTINE RAT DIGESTIBILITY ASSAY

Eight samples of meat and bone meal were evaluated for their nutrient compositions and true digestible amino acid contents using a routine rat ileal digestibility assay. The rat assay has been validated for application to the growing pig. Ileal endogenous amino acid excretion, used for the correction of apparent digestibility values to true estimates, was determined for rats given a protein-free diet, or an enzymically hydrolysed casein (EHC) based diet and after ultrafiltration of the ileal digesta. The meat and bone meals varied in their nutrient composition and in the true ileal digestibility of protein and amino acids. The gross contents (g per 100 g air-dry weight) for crude protein, ash, lysine and methionine+ cystine ranged from 47.8 to 59.3, 19.1-31.1, 2.45-3.89 and 1.25-1.93, respectively. Mean ileal endogenous nitrogen (N) and amino acid flows were significantly higher with the EHC versus the protein-free method, except for histidine and glycine. The mean ileal endogenous N flows were 1843 mug and 1124 mug g-1 food dry matter intake for rats fed the EHC and protein-free diets, respectively. The true nitrogen and amino acid digestibility coefficients based on endogenous flows determined by the EHC method were markedly higher than those determined using the traditional protein-free method. The true ileal N and lysine digestibility coefficients based on the respective endogenous flows for rats fed the EHC diet ranged from 62.7 to 88.9% and 66.4-92.3%, respectively. Values determined with endogenous flows for rats fed the protein-free diet ranged from 59.0 to 85.2% for N, and 63.2-88.9% for lysine. The variable ileal digestible N and amino acid contents of meat and bone meal emphasise the limitation of tabulated compositional values and the need for a routine relatively inexpensive digestibility assay.