Evaluation of an Aspergillus oryzae -based feed additive on enteric methane emissions and nutrient digestibility in growing steers fed a corn silage-based diet

Aspergillus oryzae-based feed additives (AOF) have long been utilized in animal diets as biotechnological tools to improve nutrient digestibility, health, and growth performance. Previous research conducted in vitro showed that the inclusion of an AOF in the substrate reduced the proportion of methane (CH4) in the gas produced. The objective of this study was to evaluate the effects of supplementation with an AOF on enteric CH4 emissions and nutrient digestibility in beef steers fed a backgrounding corn silage-based diet. Our hypothesis was that supplemental AOF may reduce enteric CH4 emissions while enhancing nutrient digestibility. Twenty-four Angus crossbred steers (10 ± 1 mo, 230.7 ± 22.8 kg of body weight) were used for the study. The treatments were: 1) Aspergillus oryzae-based feed additive inclusion at 0.032% of diet dry matter (DM; AO) and 2) No additive (CTL). The experiment was conducted as a switchback design, where each of the two periods consisted of a 21-d adaptation to treatments and facilities, followed by 5-d of enteric CH4 sampling using the sulfur hexafluoride tracer technique, and 5-d of apparent total tract digestibility determination using indigestible neutral detergent fiber as an internal marker. A 7-d washout interval was used between periods. Steers were housed in four pens, each equipped with two Vytelle feed bunks to measure individual dry matter intake (DMI). No effect of treatment was observed (P ≥ 0.10) for DMI or CH4 emissions when expressed as g/d or as g/kg of DM digested. The inclusion of AO increased (P ≤ 0.05) organic matter, neutral and acid detergent fiber, and crude protein digestibility. While the inclusion of AO in a corn silage-based diet increased nutrient digestibility, the effects on measured CH4 emissions were marginal. Further research is needed to evaluate whether supplementation of AO could reduce the emissions intensity of CH4 in g/kg of animal product.