Improving the nutritional value of oat hulls for ruminant animals with pretreatment of a multienzyme cocktail: in vitro studies.

Relatively high amounts of hydroxycinnamic acid in oat hulls, mainly ferulic acid, are believed to be inhibitory to digestion by ruminal microorganisms. Ferulic acid is produced via the phenylpropanoid biosynthetic pathway and covalently cross-linked to polysaccharides by ester bonds and to components of lignin, mainly by ether bonds. Ferulic acid also forms dimers or trimers. As a result, polysaccharides become extensively cross-linked by ferulate dimerization or trimerization and incorporation into lignin. Previous studies have shown that Aspergillus ferulic acid esterase and Trichoderma xylanase act synergistically to release ferulic acid from feruloyl-polysaccharides in complex plant cell walls of oat hulls. This activity opens the remainder of the polysaccharides to further hydrolytic attack and facilitates the accessibility of the main polysaccharide chain to cellulase, thereby increasing the release of reducing sugars. In Exp. 1, the best multienzyme cocktail (ferulic acid esterase, xylanase, cellulase, endo-glucanase [I, II], and beta-glucanase) was developed using an orthogonal experimental design, L25 (5(6)), where L = orthogonal table; 6 = factors; 5 = five levels of each; and 25 = experimental number, for further in situ and/or in vivo study. In Exp. 2, in vitro biodegradation studies with a 3 x 2 x 4 factorial arrangement of treatments were used to evaluate the responses of three feedstuffs, oat hulls or standard references (wheat straw and alfalfa hay), two particle sizes (1 mm and 250 microm), and four in vitro incubation treatments with the best multienzyme cocktail developed in Exp. 1. Addition of the multienzyme cocktail to the forages improved (P < 0.01) in vitro ruminal fluid degradability. With respect to feedstuff, the order of response (P < 0.05) to the treatments was oat hulls (+12% unit) > wheat straw (+5% unit) > alfalfa (+2% unit). This multi-enzyme cocktail seems best suited for oat hulls containing feruloyl ester bonds. In conclusion, data from this study suggest that the addition of the multienzyme cocktail to poorly digestible feeds before feeding enhanced degradation of DM.