Amino acid digestibility of meat and bone meals for broiler chickens

Variation in the apparent ileal digestibility of amino acids in 19 meat and bone meal samples, obtained from commercial rendering plants in New Zealand, was determined using 5-week-old broilers. Assay diets contained meat and bone meal as the only source of protein, and chromic oxide as an indigestible marker for the calculation of amino acid digestibility values. Correlations of chemical composition (crude protein, ash, crude fat, and gross energy) and in vitro assays (protein solubility in 0.2% potassium hydroxide and nitrogen digestibility by 0.2% pepsin hydrolysis) with ileal amino acid digestibility were also examined. Considerable variation was observed in the contents of crude protein (38.5-67.2 g/100 g), ash (13.0-56.5 g/100 g), crude fat (4.3-15.3 g/100 g), and gross energy (9.4-22.3 MJ/kg) of meat and bone meal samples. The amino acid concentrations and ileal digestibility of amino acids also varied substantially. Cystine, the first limiting amino acid in meat and bone meal, had the lowest digestibility estimates. Correlation analyses showed that the ash content was the only chemical parameter that was consistently correlated with amino acid digestibility. Digestibility of amino acids, with the exception of aspartic acid, threonine, serine, tyrosine, histidine, and cystine, was negatively correlated with ash content, with samples with high ash levels having lower digestibility. Both in vitro assay measurements were found to be insensitive indicators of variations in amino acid digestibility.