Effects of supplementing different proportions of cellulase and xylanase enzyme mixtures on intake and digestibility of high forage total mixed ration by sheep

Abstract

Exogenous fibrolytic enzymes present one way of improving fibre digestibility. Therefore, the aim of this study was to investigate the effect of adding different proportions of cellulase and xylanase enzyme mixtures on the in vitro gas and methane production characteristics, ruminal fermentation and in vitro digestibility, as well as the in vivo digestibility and rumen fermentation parameters in sheep fed with a high roughage total mixed ration (TMR). During the in vitro study Smutsfinger hay was pre-treated for 24 hours with different enzyme solutions (100% cellulose; 75% cellulase: 25% xylanase; 50% cellulase: 50% xylanase; 25% cellulase: 75% xylanase; 100% xylanase and a no enzyme control). The samples were then incubated in a shaking incubator and the gas and methane production was measured at 0, 2, 4, 8, 12, 24 and 48 hours. Addition of different proportions of cellulase and xylanase plus enzyme mixtures to Smutsfinger hay, especially the 100% cellulase treatment, increased nutrient degradability, total gas and methane production; lowered end fermentation pH and altered the volatile fatty acid (VFA) concentration. Cellulase had a much greater effect than xylanase, and its effects decrease as its concentration in the enzyme mixture decreased below 75%. During the in vivo study a TMR diets were prepared fresh every day starting with a 24hr pre-incubation period of the Smutsfinger hay with the prepared enzyme solution. The treatments were 100% cellulase; 75% cellulase: 25% xylanase; 50% cellulase: 50% xylanase, 25% cellulase: 75% xylanase; 100% xylanase and an untreated TMR (control). Before feeding each day, the pre-incubated Smutsfinger hay was mixed with the appropriate amount of concentrate to form the TMR. A digestibility trial was conducted using a 6 x 6 latin square design and rumen fluid samples were collected and preserved for VFA analysis. Addition of the mixture of 50% cellulase and xylanase plus enzyme mixture, to Smutsfinger hay increased acetate and total VFA concentrations as well as enhanced the intake and the total tract digestibility of the neutral detergent fibre (NDF) and acid detergent fibre (ADF) of the test feed. Of all the treatments, the 50:50 treatment followed by 75:25 cellulase was most effective in increasing dry matter intake in g/head/unit metabolic weight. The 50% treatment increased digestibility of dry matter (DM), organic matter (OM) and crude protein (CP), but the increase in the digestibility was not significant, the treatment however, showed significantly higher NDF and ADF digestibility, acetate production as well as total VFA production compared to the control. There was no significant difference between the treatments for propionate and butyrate. Although the different proportions of cellulase and xylanase plus enzyme mixtures generally improved TMR intake, fibre digestion and altered the VFA concentration, the best response was obtained with the 50% cellulase and xylanase plus enzyme mixture.