Effects of kaolinite-based clay minerals on methane emission from Boer goats

Methane emissions from enteric fermentation in ruminants contribute substantially to greenhouse gas emissions from the agricultural sector. Therefore, effective strategies to mitigate enteric methane production are required. This study aimed to investigate the effects of kaolinite-based clay mineral (KCM) supplementation on methane emissions, rumen fermentation, and the rumen microbiome in goats. Eight Boer goats (39.7 ± 2.81 kg) were used in a 2 × 2 crossover design. The goats were fed a total mixed ration at 2% of body weight (dry matter basis), either without CM (CON) or with 1% KCM supplementation (TRT). Goats were adapted to the diets for 10 days. Each goat was housed in an open-circuit respiration chamber to measure methane emissions, dry matter intake (DMI), total-tract apparent digestibility, and rumen microbial composition. After methane measurements, rumen fluid samples were collected via stomach tube for fermentation analysis. Methane emissions (g/day) did not differ between CON (20.37 g/day) and TRT (21.29 g/day). The methane yield per unit of DMI in CON and TRT was 27.20 and 29.70 g/kg DMI, respectively, and did not differ between KCM and control. Except for a significant reduction in ruminal ammonia-N concentration with KCM supplementation (CON 19.58 mg/100 ml, TRT 16.21 mg/100 ml), rumen pH, volatile fatty acid profiles, and total-tract apparent digestibility were not altered. KCM supplementation induced minor shifts in rumen microbial community composition but did not significantly alter microbial diversity or rumen fermentation, owing to functional redundancy within the rumen microbiome. In conclusion, KCM supplementation at 1% of the diet did not reduce enteric methane emissions in goats, despite minor alterations in ammonia-N concentration and microbial composition. These results suggest that higher inclusion levels, longer adaptation periods, or combined feed additive strategies may be required to achieve methane-mitigating effects in goats.