Relationship between enzymic activities and in vitro degradation of alfalfa hay and corn silage

A meta-analysis of data from in vitro studies was performed to identify the key enzymic activities in feed enzyme additives, and their dose rates, that improve degradation of alfalfa hay and corn silage. All studies were conducted in our laboratory using similar in vitro procedures and all enzyme assays used the same conditions (pH 6.0 and temperature 39 °C) and substrates. Data from 8 research studies with 83 enzyme treatments using 45 enzyme products were summarized for alfalfa hay, and data from 6 research studies with 61 enzyme treatments using 23 enzyme products were included for corn silage. Added endoglucanase, exoglucanase, xylanase and protease activity, in addition to endoglucanase:xylanase ratio, were included in the analyses as candidate key enzymic activities. Incremental gas production (IGP) and improvement of dry matter degradability (IDMD) and neutral detergent fibre degradability (INDFD) were included as response variables. Initially, relationships between added enzymic activities and response variables were determined by linear regression analysis. Then, a mixed model analysis accounting for the random effect of study and linear and quadratic effects of added enzymic activities was used to describe the relationships. For alfalfa hay, simple linear regression analysis showed low, but significant, relationships between IGP and added endoglucanase, xylanase or exoglucanase (r2 ≤ 0.09, P<0.05) with no relationships between enzymic activities and IDMD or INDFD. In contrast, mixed model analysis showed a positive linear relationship (P<0.05) between IGP and added protease activity (r2 = 0.50) and between INDFD and exoglucanase activity (r2 = 0.75). For corn silage, simple linear regressions showed low, but positive relationships (P<0.05), for IDMD with endoglucanase (r2 = 0.08), exoglucanase (r2 = 0.12), or endoglucanase:xylanase ratio (r2 = 0.23) and for INDFD with added endoglucanase (r2 = 0.09), exoglucanase (r2 = 0.34), endoglucanase:xylanase ratio (r2 = 0.08), and protease (negative effect, r2 = 0.06). Mixed model analysis confirmed linear relationships (P<0.05) with these activities, but improved predictions (IDMD: R2 = 0.39–0.49; INDFD: R2 = 0.36–0.56). For both forages, quadratic effects of added enzymic activities only marginally improved the prediction equations in most cases. Overall, added activities of exoglucanase had the strongest, positive, association with fibre degradation for both forages.