Effect of ash content on protein quality of meat and bone meal

The effect of ash concentration on amino acid (AA) composition, true AA dig estibility, and protein efficiency ratio (PER; weight gain per unit of prot ein intake) of meat and bone meal (MBM) was evaluated. Commercially rendere d MBM samples containing 16 to 44% ash were obtained from two sources. Addi tional samples of MBM varying in ash from 9 to 63% were obtained by chlorof orm floatation or lab screening of a beef crax sample. Protein quality of s elected MBM samples was assessed by determining true AA digestibility using the precision-fed cecectomized rooster assay and by a PER chick growth ass ay wherein chicks were fed 10% CP diets containing a MBM as the only source of dietary protein from 8 to 18 d of age. Increases in Ala, Pro, Gly, and Arg as a percentage of CP were observed in all MBM samples as ash percentage increased, with Pro and Gly accounting fo r most of the increase. In contrast, the levels (% of CP) of all essential AA, other than Arg, decreased as ash level increased. For example, Lys conc entrations per unit of CP decreased from 5.7 to 4.0% as ash increased from 9 to 63%. There was little or no effect of ash content on AA digestibility of MBM varying in ash from 9 to 44%. The PER of MBM markedly decreased from 3.34 to 0.72 as ash increased from 16 to 44%, and most of the effects of a sh on PER were not due to differences in dietary Ca and P levels. The results indicate that the reduction in protein quality of MBM as ash co ntent increases is almost entirely due to a decrease in analyzed essential AA per unit of CP, not a decrease in digestibility of AA.