LIMITING AMINO-ACIDS IN MEAT AND BONE AND POULTRY BY-PRODUCT MEALS

In situ, digestion, and growth studies were conducted to evaluate four meat and bone meals and six poultry by-product meals as sources of es cape protein and to predict the first-limiting amino acid for growing calves. Escape protein values, determined by 12-h in situ incubation, ranged from 41.7 to 51.0% of CP for meat and bone meals; poultry by-pr oduct meals ranged from 32.0 to 39.8%. True protein digestion in the g astrointestinal tract of lambs differed among protein sources (P < .05 ), ranging from 79 to 95%. In each of three growth trials, 60 steers ( 258 +/- 24, 241 +/- 23, and 230 +/- 16 kg for Trials 1, 2, and 3, resp ectively) were supplemented with 4 of the 10 protein sources along wit h a urea supplement. Protein sources were fed at 30, 40, 50, and 60% o f the supplemental CP, with urea supplying the remainder. Protein effi ciency differed among treatments (P < .10), ranging from .61 to 1.55. Amino acid composition was determined for each protein source, and the individual metabolizable amino acids were regressed on the protein ef ficiency values. Escape protein values were correlated (R-2 = .75) wit h protein efficiency but had a negative slope. Metabolizable methionin e was the only amino acid moderately correlated (R-2 = .40, slope = 1. 9) to protein efficiency, whereas other amino acids either correlated poorly or had negative slopes. These data indicate that the protein va lue of meat and bone meal and poultry by-product meal is limited by th e amount of metabolizable methionine they contain.