Abstract/Summary

Garlic contains bioactive organosulphur compounds reported to be effective in reducing methane (CH4) emissions, but garlic dietary supplements are inconsistent in reducing rumen CH4 production, possibly due to matrix or inclusion level effects. To assess this, the effects of garlic matrix (freeze-dried, FD; garlic extract, GE), source (Chinese; Spanish) and inclusion level (30, 60, 120 mg extract/g DM) on gas, CH4 and volatile fatty acid (VFA) production were measured using an in vitro gas production rumen fermentation system. Garlic extract was extracted from both sources, and this or FD garlic was incubated at the same oil inclusion levels in flasks with a dried, milled total mixed ration (TMR; forage:concentrate 50:50, DM basis) for 72 h, with strained rumen fluid and incubation medium (1:9, v/v). Flasks containing just TMR (control, CON) or no substrate (negative control) were also included. Gas pressure measured at intervals during the fermentation was converted to volume, and gas samples were analysed for CH4 concentration using gas chromatography. Dry matter degradability and VFA concentrations in the medium were measured after 72 h. In vitro gas and CH4 production was fitted to previously published models to obtain gas production kinetic characteristics. Data were analysed using linear mixed models, with processing method, origin, and their interaction as fixed, and run as random factors. Dry matter degradability (g/kg DM) was higher (P < 0.001) with all treatments (both FD and GE) for both Chinese and Spanish garlic across all inclusion rates (79.8 and 80.1) compared to CON (78.3). Total gas production (ml) was higher (P < 0.05) in the GE treatments than the CON (145.2) for both Chinese and Spanish garlic (164.1 and 169.1, respectively). Acetate:propionate ratio was lower (P < 0.001) for both garlic treatments and origin across all inclusion rates (2.4-2.9) compared with CON (3.0). Increasing the inclusion rate did not change in vitro CH4 production compared with CON. The results suggest that the bioactive components in garlic, when presented in an extracted matrix, might enhance overall fermentation efficiency without directly mitigating CH4 emissions. This finding implies that while garlic-based supplements might not consistently reduce CH4 emissions, they could be used to improve feed efficiency and animal productivity in ruminant systems.