Seasonality of fibrolytic enzyme activity in herbivore microbial ecosystems
Fibre (cellulose, hemicellulose and lignin) is the most abundant polysaccharide in nature and is hydrolysed by gut micro-organisms of herbivores because they can produce a set of extracellular enzymes. This study examined seasonal changes in the fibrolytic enzyme activity of microbial ecosystems of five herbivores (buffalo, cow, impala, wildebeest and zebra). Crude protein extracts obtained from the aforestated ecosystems were assayed for exocellulase, endocellulase, cellobiase and xylanase by incubating with crystalline cellulose, carboxymethylcellulose, p-nitrophenyl ß-1, 4-D-gulcopyranoside and xylan at optimum pH (5.5 to 6.5) for 1, 2, and 48 h, respectively. The specific activities (μg reducing sugar/mg crude protein) of all enzymes varied (p<0.001) among ecosystems and between seasons. Generally, the exocellulase specific activities in all ecosystems increased from summer to winter whilst the specific activities of endocellulase and xylanase decreased. The cellobiase activity decreased for buffalo and impala but increased for the others. It is only the zebra that showed the most superiority to the cow for all enzyme systems. These results suggest that in vitro digestion of fibre would depend on the season the ecosystem is collected and the source of the ecosystem. Microbial ecosystem from the zebra is one with the highest activity that could benefit the ruminant production system.
Keywords: Seasonality, herbivores, microbial ecosystems, enzymes