In vitro studies on degradation of crude protein from different forage legumes, perennial ryegrass and maize

Fresh forages show a large variation in protein degradability. The objective of the present study was to determine the crude protein degradation rate at silage maturity of white clover, red clover, kura clover, alfalfa, birdsfoot trefoil, perennial ryegrass as well as maize using the modified in vitro inhibitors method. The degradation rate allows the determination of the amount of escape protein (UDP) as well as the amount of the metabolizable protein in the small intestines (nXP). The N contents of the forage plants varied as expected, showing a range from 1.1 to 1.9% N in the DM for grasses and maize and above 3.5% N for forage legumes. The estimated degradation rates varied from 2.6 to 8.2%/h for the forages. Birdsfoot trefoil showed the lowest degradation rate, differing significantly from all other forages. No significant differences were found between the other forages. The calculated UDP contents using passage rates of 4 and 8 %/h showed the highest values for birdsfoot trefoil. The comparison of the UDP values estimated by the present study with the tabulated values show a systematic deviation, i.e. the estimated values are systematically higher, especially for forage legumes. Reasons for this divergence are discussed. The in vitro method used in the present study showed to be useful to estimate the degradation rate of forage legumes, grass and maize. Advantages of the method are related to the application of a variable range of passage rates to estimate UDP and nXP.

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