The amino acid profiles of the whole plant and of four plant residues from temperate and tropical forages.
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This study compared the amino acid (AA) profile of five residues (original forage, borate-phosphate buffer residue (BPR), neutral detergent fiber residue with (NDF+) and without (NDF-) sodium sulfite, and acid detergent fiber residue (ADF). Fourteen grasses and legumes from tropical and temperate regions were used in this study. The use of sodium sulfite did not affect the NDF concentration, but the NDF insoluble protein was lower (P < 0.05) in the NDF+ than in the NDF- (3.9 vs 4.5% DM, respectively). For all of the amino acids tested, the amino acid content, expressed as a percentage of CP, was lower in the ADF residue than in the original forage. There were no differences in the amino acid concentrations of the NDF- and NDF+ extracts (P > 0.05). Only in the case of methionine was there a difference in the amount of amino acid when the original forage was compared with the BPR (1.84 vs 1.45 % CP). When the AA profile of each residue was corrected for the AA content of the ADF, no difference was observed between the AA profile of the original forage and of the BPR (P > 0.05). Similar to the result without correction for the amino acids in ADF, the AA profiles of the NDF+ and NDF- fractions were similar (P > 0.05). From this result, we infer that the sodium sulfite had similar effects on all AA in the NDF residue that we tested. There were differences in amino acid concentrations in the original forage and the NDF residues for several amino acids (Met, Cys, Lys, Thr, Arg, Ile, Leu, and Phe) (P < 0.05). When the amino acid values of the original forage and the BPR were used with animal data in the Cornell Net Carbohydrate and Protein System model, few differences in animal predicted performance were evident. These findings suggest that the AA profile of the original forage can be used to predict the AA profile of the undegraded intake protein instead of using the borate-phosphate buffer residue for amino acid analyses. This would simplify obtaining feed amino acid values for use in the Cornell Net Carbohydrate and Protein System.