Submitted to: British Society of Animal Production Meetings and Proceedings
Publication Type: Review Article
Publication Acceptance Date: December 15, 1998
Publication Date: N/A
Technical Abstract: New ruminant feeding systems being developed in Europe and North America have greatly increased the need for rapid measurement of rate and extent of ruminal digestion of feed carbohydrates and proteins. This has increased use of cell-free enzymes to assess ruminal breakdown of carbohydrates and proteins. The simplest model describing ruminal digestion divides these nutrients into three fractions: A (soluble), B (digestible), and C (indigestible). Fractions A, B and C sum to 1.0; proportion of digestible fraction B that is degraded is given by: [kd / (kd + kp)], where kp and kd are, respectively, rates of ruminal passage and digestion. Successful, cell free enzyme systems should yield accurate estimates of the fractions and rates and, where appropriate, lag time. In vivo digestibility of OM and energy was predicted accurately when feed samples were pre-treated with acid-pepsin or neutral detergent solution then incubated with cellulase from T. viride. Both techniques have predicted in vivo digestibility more precisely than Tilley and Terry methods. Many cell-free proteases have been tested to estimate ruminal protein degradability. Effectiveness of proteases was assessed by correlating proportion of feed N solubilized after specific incubation times with extent of in situ protein degradation. The broad specificity protease from Streptomyces griseus has been used most extensively in incubations at pH 8.0. However, better correlations have been reported for ficin, bromelain, papain, and neutral proteases of fungal and bacterial origin in incubations at pH more similar to the rumen. Prior treatment with amylases improved correlations for concentrate feedstuffs. As yet, cell-free proteases have not accurately predicted the rates and extents of protein degradation observed in the in vivo rumen.