Supplementation with Aspergillus oryzae decreases intestinal and fecal methane emissions and affects the production performance of beef cattle

Abstract This study aimed to assess the impact of Aspergillus oryzae supplementation on CH₄ emissions and the production performance of beef cattle. Sixteen healthy Simmental crossbred steers (552.38 ± 35.48 kg) were randomly assigned to either a control group (CG, basal diet) or an A. oryzae group (AO, basal diet + 6 g A. oryzae per head daily). CH₄ emissions from enteric fermentation and manure, production performance, nutrient and energy digestibility, rumen fermentation parameters, and microbial populations were evaluated. The results showed that A. oryzae supplementation did not significantly affect average daily gain (ADG) or dry matter intake (DMI), though ADG increased by 11.11%. The AO group exhibited a 36.41% increase in apparent NDF digestibility (P < 0.05), a significant reduction in ammonia-N (P < 0.05), and elevated rumen fungi and Butyrivibrio fibrisolvens populations while reducing protozoa and methanogens; CH₄ emissions from enteric fermentation and manure decreased by 18.78% (P < 0.05) and 56.55%, respectively. In summary, supplementation with A. oryzae effectively lowers CH₄ emissions both enteric fermentation and manure without compromising beef cattle production performance.