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.
