Predicting ruminal degradability of lucerne and grass forage protein from in vitro solubility with non-specific bacterial protease or pancreatin
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Research Institute on Animal Production, Department of Animal Nutrition and Physiology, Sarego 2, 31-047 Kraków, Poland
Publication date: 1995-11-06
J. Anim. Feed Sci. 1995;4(4):341-350
Samples of lucerne (25) from the primary growth and 2 regrowths and samples of grass (9) from the primary growth were harvested in successive stages of maturity within one vegetation season and were used to test the applicability of protein solubilization during incubation with a non-specific protease from Streptomyces griseus (Sigma type XIV ) or porcine pancreatin to predict in sacco ruminal degradability of crude protein (CP) in dried forage. The effective degradability (ED) of protein in the forage, calculated at k = 0.06 h-1, ranged from 63 to 88%. The conditions for protease XIV activity given by Krishnamoorthy et al. (1983) and Aufrere and Carthailler (1988), at constant enzyme concentration in the incubation medium and short incubation period, were not suitable for predicting variability in in sacco protein degradability of lucerne due to morphological changes or growth type (R2 = 0.183, P = 0.03, RSD = 5.94). The results were better when a constant ratio of enzyme to protein in a sample was maintained (4 U of protease per 100 mg of protein) and duration of incubation was extended to 24 h (R2 = 0.713, P < 0.001, RSD = 3.52). However, the best fit between enzymatic solubility and effective degradability of lucerne protein was obtained using pancreatin (ca. 5 U of trypsin per 0.5 g of dry forage): R2 = 0.830, P < 0.001 , RSD = 2.71. Validation of regression equations with samples of grass forage indicated that solubility with pancreatin was superior to the action of protease from S. griseus in predicting ruminal degradability of forage determined in situ in cows (R2 and RSD = 0.96 and 1.64% vs. 0.59 and 5.15%, respectively). The regression equations between ED (Y, %) and enzymatic solubility of protein (X, %) for the combined sets of lucerne and grass samples (n = 34) were for pancreatin: Y = 1.18 X -10.97, R2 = 0.882, P < 0.001, RSD = 2.84; for protease: Y = 1.00 X + 2.93, R2 = 0.544, P < 0.001, RSD = 5.97.
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