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, enzyme

The in vitro fermentation of maize stover as affected by faecal bacteria obtained from ungulates

The effect of different inoculum sources, obtained from the faeces of ungulates, i.e. horses (H), wildebeest (WB) and zebra (ZB) and combinations of inoculum sources on the fermentation of maize stover (MS) was investigated. Combined sources (CS) were: (1) H+WB, (2) H+ZB, (3) WB+ZB and (4) H+WB+ZB. Fresh faecal inocula were cultured in the laboratory on MS and lucerne (mixed in 1 : 1 ratio) with salivary buffer for 72 h at 38 °C prior to application as an inoculum or extraction of crude protein (CPZ) for enzyme assays. Crude protein was precipitated using 60% ammonium sulphate and analyzed for exocellulase, endocellulase and hemicellulase specific activities (μg reducing sugar/mg CPZ). An in vitro fermentation study was done by transferring 33 mL of laboratory  cultured faecal inoculum into 67 mL of salivary buffer containing 1 g MS and incubating for 72 h at 38 °C. Exocellulase specific activities differed among the seven inoculum sources. Exocellulase activity ranked the different microbial sources according to their fibrolytic potential as follows: 1 > 2 > 4 > H > ZB > WB >3. Total gas, true degradability (TD), microbial yield and total short chain fatty acids (SCFA) were higher in the CS than in the individual systems. Systems 1 and 3 had the highest TD (714mg/g CPZ) and total SCFA (680 mg/g CPZ), respectively. True degradability, total gas, total SCFA, partitioning factor and degradability efficiency ranked the microbial ecosystems according to their fibrolytic potential as follows: 3 > 1 > 4 > WB > 2 > ZB >H. Inoculum sources differed in fibrolytic digestion, with microbes from CS (1) and (4) proving to be the best. Further investigation is essential towards using inoculums sources as possible feed additives in ruminants.Keywords: Faecal digesta, fibrolytic competenc

The effect of tannin with and without polyethylene glycol on in vitro gas production and microbial enzyme activity

The aim was to determine the effect of tannin on the nutritive value and microbial enzyme activity in vitro. The leaves and pods of the Acacia sieberiana and Acacia nilotica trees were subjected to chemical analysis and in vitro fermentation with and without polyethylene glycol (PEG; 35 mg/g). Gas production (GP), true degradability (TD) and the proteolytic and fibrolytic enzyme activities in digesta were determined. Data analyses accounted for the effects of feed type, feed fraction, PEG and their interactions. Leaves and pods had similar NDF and ADF contents in A. sieberiana but differed in both attributes in A. nilotica. The leaves had a higher protein, but lower condensed tannin (CT) contents than the pods. A. sieberiana had more CT than A. nilotica, but both had a similar maximum GP. PEG increased the maximum GP, stimulated GP from the soluble fraction and shortened the lag phase. PEG increased the TD for leaves and pods of A. sieberiana, but suppressed TD in fractions of A. nilotica. PEG also increased the activity of protease enzymes, xylanase, endo- and exocellulases, indicating that tannins depress the digestibility of feeds partly by suppressing the activity of these enzymes. Consequently, condensed tannin depressed the digestibility of feed in the rumen by affecting the activity of enzymes involved in carbohydrate and protein breakdown, the effects of which could be reduced with the use of PEG.Keywords: Protease, xylanase activity, endo- and exocellulase activity, fibrolase, degradation kinetics, PE