The nutritional value of browse foliage from the Thorny Kalahari Dune Bush veld of South Africa is not characterized. Most of this browse species is rich in tannin, but still palatable, and is consumed by ruminants during the dry season, as well as having a role to play in mitigating enteric methane emission from ruminants. In this study, the rumen methane mitigation potential of 19 browse species foliage collected from the Thorny Kalahari Dune Bush veld, was analyzed in terms of chemical composition, in vitro fermentation, digestibility and methane production. In vitro gas and methane production and organic matter digestibility (IVOMD) were determined by using rumen fluid collected, strained and anaerobically prepared. A semi-automated system was used to measure gas production (GP) from each browse species by incubating 400 mg samples in a shaking incubator at 39 °C with or without inclusion of 400 mg of polyethylene glycol (PEG). Data for all the parameters collected were statistically analyzed using the SAS (9.0) general linear model (GLM) procedure, and differences between foliage species were determined using Duncan’s multiple-range test. Acacia luederitziiand Monechma incanumshowed the best potential for decreasing methane production by up to 90 % after 48 h of incubation. The secondary components (mainly tannins) of the browse species appeared to have a significant effect on volatile fatty acids (VFA), methane and gas production as judged by the comparison of samples incubated with or without PEG inclusion. The substantial amount of crude protein (CP) content coupled with their anti-methanogenic effect during fermentation would make these browses a potential mitigation option for small scale farmers and pastoralists in sub-Sahara Africa. However, it is also very important that systematic and strategic supplementation in a mixed diet should be looked at as the way forward in terms of best utilization.

In recent decades supplementation of animal feeds with exogenous fibrolytic enzymes has substantially improved digestibility and animal performance. However, information related to associated methane production is limited and inconsistent. This study evaluated the effect of cellulase and xylanase enzymes on in vitro methane production of Eragrostis curvula hay, maize (Zea mays) stover and a total mixed ration (TMR) at seven levels of the two enzymes. Feed samples were incubated for 2, 12, 24 and 48 h in an in vitro batch culture with buffer and rumen fluid, and fibrolytic enzymes. Gas production was measured using a pressure transducer connected to a data tracker, while methane gas was analysed using a gas chromatograph which was calibrated with standard CH4 and CO2. Increases in the level of enzyme application resulted in increases in gas volume, total volatile fatty acid (VFA) production, dry matter (DM) disappearance and associated increases in methane production. The linear increase in percentage and volume of methane production in tandem with increases in level of enzyme application might be due to increased fermentation, and organic matter degradability that resulted in a shift in VFA production towards acetate. Considering the efficiency of DM and neutral detergent fiber degradation and production of associated VFA with levels of enzymes, the use of 1 mg g−1 DM of enzyme can be a good option for the feeds tested. However, they cannot decrease methane production. It will be very important to consider other hydrogen sinks that can capture directly extra H+ produced by the addition of enzyme so that their supplementation could be very efficient and environmentally sound.