Effective degradability and prediction of intestinal digestibility in rumen for undegraded feed crude protein

Effective degradability of crude protein and parameters of degradability of rape cake, rapeseed meal, sunflower meal, soybean meal, wheat meal and wheat bran were determined by an in situ method in three bulls; solubility of crude protein of these tested feed was measured in 0.15 M of NaCl solution (pH 6.5). Intestinal digestibility of undegraded crude protein (after 16h incubation in the rumen) was determined by an in vitro method, mobile bag method and by an in vivo method in rats. The proportion of soluble N fraction in the total N content ranged from 19% for soybean meal to 68% for rape cake, which had the highest crude protein degradability (more than 80%). Intestinal digestibility of undegraded residues determined by different methods increased while ruminal degradation decreased. More than 80% of soybean meal crude protein from the residual amount of undegraded N were digested in rumen. An enzymatic method yielded the highest values of intestinal digestibility. The smallest differences between the methods were calculated for rapeseed meal (ca. 2%) and the largest for sunflower meal (ca. 10%).