| Summary: | The objective of this study was to evaluate 20 protein feeds grouped in forages, vegetal by- products and animal by-products used for ruminant diets. Protein fractions (PF): A, non-protein nitrogen (NPN); B1, buffer-soluble protein; B2, buffer-insoluble, NDF-soluble protein; B3, NDF-insoluble, ADF-soluble protein; and C, ADF-insoluble protein, were determined for each ingredient. Protein composition was correlated with total gas production in vitro (GP), gas production rate (S), lag time (L), DM disappearance (DMDIV) and residual protein (RPIV). The completely randomised designed was analysed using mixed proc. and Tukey contrasts. Forages contained 18.29, 7.86, 66.00, 2.96, 4.89% of fractions A, B1, B2, B3 and C, respectively. Vegetable by-products contained 22.55, 4.55, 59.51, 8.84, 4.55% of each fraction, in the same order. Animal by-products contained 19.13, 4.52, 70.24, 3.74, 2.37% of each fraction, in the same order. Vetch, wheat bran and poultry litter had the greatest Vmax in each group. Vmax was correlated (P≤0.01) with total protein (r = -0.45), ADF (r = 0.27) and DMDIV (r = 0.61). In conclusion, there were differences in protein composition and kinetics of in vitro gas production among ingredients.
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