Effects of Aspergillus niger and Its Compound Preparations on Methane Emissions and Gastrointestinal Microbiota in Heat-Stressed Holstein Bulls

The livestock sector is a major source of methane, a potent greenhouse gas, while heat stress impairs ruminant health. This study evaluated the efficacy of <i>Aspergillus niger</i> (AN) and its compound preparation (CP) as feed additives to mitigate methane emissions and heat stress in Holstein bulls. Twenty-four bulls were assigned to a control group (CON), a group supplemented with 6 g/d of AN, and a group with 20 g/d of CP. Methane emissions were measured using the SF₆ tracer technique. Blood and ruminal fermentation parameters were also analyzed. Results showed that both AN and CP significantly reduced total methane emissions, emissions per unit of body weight, and per unit of dry matter intake compared to CON. Supplemented groups had significantly lower rectal temperatures and higher superoxide dismutase activity, with AN also increasing total antioxidant capacity. AN groups showed increased total volatile fatty acids, acetate, and propionate. Microbiota analysis revealed significant beta-diversity shifts with differential taxon enrichment. In conclusion, <i>Aspergillus niger</i> and its compound preparation effectively reduce enteric methane and alleviate heat stress by boosting antioxidant defenses and modulating rumen function, offering a dual-benefit strategy for sustainable ruminant production.