Effect of Fibrolytic Enzyme Application on the Digestibility of Corn Silage, Alfalfa Hay, Concentrates, and Complete Diets under Simulated Ruminal and Preruminal Conditions

Previous work showed that when added to the total mixed ration (TMR) prior to feeding, a fibrolytic enzyme containing 733U/ml of endoglucanase activity, 3630 U/ml of xylanase activity, and 0.0002 umol/mg/minute of esterase activity improved dry matter digestibility (DMD) and neutral detergent fiber digestibility (NDFD) and the level and efficiency of milk production by dairy cows. This study determined if the enzyme exerts its hydrolytic effect on different dietary substrates prior to ingestion or within the rumen and determine which dietary components were most affected by enzyme action. Substrates evaluated included corn silage (CS), alfalfa hay (AR), low (LC) and high (HC) - energy concentrates (22 and 37% corn meal) and low- (33%) and high- (48%) concentrate total mixed rations (TMRL and TMRH). Substrates were incubated in a buffer or a buffer-enzyme solution in triplicate for up to 24 h and chemical composition and DM disappearance were measured. In addition, DMD and NDFD were determined after untreated or enzyme-treated substrates were incubated in water (W) or ruminal fluid (RF) for a further 24 h after the initial incubation in the buffer or buffer-enzyme solution. Application of the enzyme reduced concentrations of NDF and hemicellulose, increased water-soluble carbohydrate (WSC) concentration and DM disappearance. Incubation of enzyme-treated substrates in RF resulted in greater DMD than incubation in W except for AH, which had similar DMD in both media. Enzyme addition increased DMD and NDFD in W by 10 and 39% respectively, but had no effect on DMD and NDFD in RF; suggesting that preingestive effects of the enzyme were greater than ruminal effects. Enzyme effects on NDF, WSC, and hemicellulose concentration or DMD and NDFD in W or RF did not depend on the substrate. Therefore, this study provided no evidence that the enzyme preferentially hydrolyzed specific substrates and it suggested that preingestive effects of the enzyme were greater than ruminal effects under the conditions of this study.