Effect of microbial ecosystem from wild herbivores browsing tanniferous plants on goat rumen fibrolytic activity

Abstract

Ruminant have developed advanced microbial ecosystem for digesting fibrous feedstuffs over the past years. The efficiency of harnessing energy from these forages is still a major problem as less than 60% of forages consumed are still passed out as faeces. Many factors have been associated with the poor breakdown of these forages including; complexity of fibre in forage types, inefficient microbes, microbial population, low rumen pH and presence of anti-nutritional compounds (lignin and alkaloids, saponnins and tannin). Therefore, understanding microbial ecosystems’ activities in ruminants is an essential step towards improving tanniferous browsers’ utilisation especially in goats which are often supplemented in winter during forage shortages. The study was conducted to identify potential rumen microbial ecosystems browsing tanniferous forages that might have evolved in their ability to degrade plant fibre in the presence of tannin that can potentially be used to improve domestic goat browse utilisation. Experiment 1 investigated the fibrolytic potential of microbial ecosystems giraffe, kudu, impala and consortia (A1 (giraffe + kudu, 1:1), A2 (giraffe + impala, 1:1), A3 (kudu + impala, 1:1), A4 (giraffe + kudu + impala, 1:1:1)). Crude protein enzyme extracts (CPZ) from fresh faecal samples were precipitated by 60% ammonium sulphate and assayed for exocellulase, endocellulase and hemicellulase by incubating with crystalline cellulose, carboxymethyl cellulose and xylan at 38℃ at pH of 5.5 for 1, 2, and 48 h, respectively. Enzyme specific activities were defined as μg of reducing sugar/mg CPZ. In vitro fermentation study was done by transferring 33 mL of fresh faecal inoculum into 67 mL of salivary buffer containing 1 g Acacia sieberiana and incubating for 72 h at 38℃. Apparent degradability (APD), true degradability (TD), neutral detergent fibre degradability (NDFdeg), acid detergent fibre degradability (ADFdeg), microbial yield (MY), metabolisable energy (ME) and total gas emitted (Gas) were measured. Cellulases, hemicellulase and in vitro degradability studies showed that microbial ecosystems from wild browsers (especially impala) and consortia possess a higher (P<0.05) potential to digest tanniferous forages with less enteric gas production than observed in goats, hence could be exploited as feed additives for improving digestibility and reducing enteric gas production in goats. In experiment 2, the effect of tannins on the fibrolytic potential of microbial ecosystems from goats, wild giraffe, kudu, impala and consortia (A1, A2, A3 and A4) were monitored. The method was the same as in experiment 1 except for the addition of 10% tannic acid. A microbial ecosystem treated with 10% tannin showed higher (P<0.05) fibrolytic enzyme activities and

digestibility parameters compared to the control. The goat ecosystem showed some degree of adaptability to increased tannin but microbial ecosystems from wild browsers (impala and kudu) and consortia (A1, A2 and A3) showed a higher potential to digest tanniferous forages. The results demonstrated that wild herbivores especially impala and A1 consortia can tolerate minimal changes in tannin concentrations. Experiment 3 assessed the effect of in vitro inoculation of goat microbial ecosystems with inocula from wild herbivores (impala, kudu and giraffe) on in vitro fermentation, gas production and cellulase activity in goats. The method was similar to that of experiment 2 but for goat microbial consortia (N1 (goat + impala, 1:1), N2 (goat + kudu, 1:1), N3 (goat + giraffe+ kudu, 1:1:1) and N4 (goat + giraffe + kudu + impala, 1:1:1:1)). Manipulation of the goat ecosystem with microbes from the wild generally increased (P<0.05) cellulase and hemicellulase activities as presented by their high hemicellulase, endocellulase and exocellulase activities. The highest (P<0.05) NDFdeg, ADFdeg and TD were observed in N3 while HEMdeg and CELLdeg were high in the N1ecosystem. Therefore, wild ruminant browsers may be harbouring important potential fibrolytic microbial population with relatively high tannin tolerance which can be used to improve the browses digestibility of goats. The final experimental chapter monitored the effect of adding polyethylene glycol 4000 (PEG) to goat microbial consortia in vitro degradability of tanniferous feeds. The results showed that 5% PEG supplementation generally increased (P<0.05) hemicellulase, endocellulase and exocellulase activities in goats’ consortia when compared to the control. Digestibility of fibre was lower for diets not treated with PEG. Apart from N3, PEG increased (P<0.05) dry matter degradability of Acacia sieberiana but not microbial yield. The improvement of enzyme activities and dry matter digestibility upon addition of PEG in goat consortia highlights the inhibitory effects still possessed by tannins even when inoculated with potential fibrolytic microbes from wild browsers. Therefore, microbial ecosystems from wild browsers can contribute potential fibrolytic microbes with relatively high tannin tolerance that can improve forage digestibility and reduce enteric gas production in goats.