Effects of multiple exogenous enzyme products on in vitro fermentation by rumen microbes in batch and continuous culture fermentation

Abstract

Research has demonstrated that supplementing exogenous enzymes to ruminants has potential to improve feed digestion and animal performance. Enzyme products with fibrolytic, proteolytic and amylolytic activities and diets with diverse composition have been used to test enzyme efficacy. Responses to these conditions have been variable. A series of in vitro experiments were designed to 1) screen enzyme products in ruminal batch culture to determine effects on digestibility and gas production and 2) further examine effective enzymes in dual-flow continuous culture to determine their effect on microbial fermentation. In Exp. 1, seven treatments, including a multi-enzyme blend (MEB), ferulic acid esterase (FAE), protease (PRO), α-amylase (AAM), β-glucanase (BGL), xylanase (XYL) or control (CON), were added to each of 3 diets with forage:concentrate ratios of 50:50 (Diet 1), 30:70 (Diet 2) or 10:90 (Diet 3), at 6 dosage rates (0, 125, 250, 500, 1000 and 10,000 mg of enzyme/kg of diet DM) in batch culture. Dose was removed from analysis and all doses were combined and examined together. In vitro total dry matter digestibility (IVTDMD) was greater (P < 0.05) for BGL compared with all other treatments in Diet 1 and Diet 2. In Diet 3, BGL was greater (P < 0.05) than AAM and CON. Control and XYL had greater (P < 0.05) total gas production than MEB, FAE, and AAM. Rate of gas production (mL/h/g of DM) was also affected (P < 0.05) by diet and enzyme for the first 24 h of fermentation with CON having the fastest rate at 3 h, generally. Overall, BGL increased digestibility without generating as much gas as CON. In Exp. 2, BGL and PRO from Exp. 1, a cellulase (CEL) preparation and control (CON) were examined in eight dual-flow continuous culture over 3 periods. The diet was a 40:60 (forage:concentrate) and enzyme was supplied at 1000 mg/kg of diet DM. Digestibility of apparent DM and OM tended to be greater (P < 0.10) for CON compared with CEL. Volatile fatty acid (VFA) concentration and nitrogen metabolism were not affected (P > 0.05) by enzyme treatment. In summary, the increase in DM and OM digestibility found with BGL and other effects of enzymes on fermentation in batch culture were not observed in dual-flow continuous culture.