The essential oil blend Agolin Ruminant L reduces methane production in vitro and in vivo when included in the drinking water of cattle

Two experiments were conducted to determine the potential for the essential oil blend Agolin Ruminant L (Agolin) to reduce enteric methane (CH4) emissions from beef cattle when delivered via drinking water. Experiment 1 evaluated aqueous solutions of Agolin (50 mg/L) and a nonprotein nitrogen and mineral solution (uPRO ORANGE [uPRO]; 1.7 mL/L) individually and in combination, where Agolin was added to concentrated uPRO at 3%, 4.5%, and 6% Agolin (w/w) prior to dilution with water at 1.7 mL/L, for a total of 5 treatments. These were incubated for 48 h with a medium-quality Rhodes grass (Chloris gayana) hay substrate, with gas production, CH4 concentration in gas, and digestibility measured in vitro. In experiment 2, Droughtmaster steers (n = 24) were fed a basal diet of Rhodes grass hay and were allocated to 1 of 3 water treatments (n = 8 per treatment) supplemented with either uPRO (2.27 mL uPRO/L water), or 1 of 2 inclusion rates of Agolin in combination with uPRO (2.27 mL uPRO and 6 μL Agolin/L water or 2.27 mL uPRO and 24 μL Agolin/L water) with enteric CH4 emissions, feed and water intake, and live-weight gain (LWG) measured over 56 d. In experiment 1, the inclusion of Agolin in uPRO at 6% (w/w) resulted in a reduction in CH4 production (15.8%; P = 0.003) and the proportion of CH4 in the gas produced (24.5%; P < 0.001). In experiment 2, steers consuming the lower quantity of Agolin via drinking water had a 16.4% (P = 0.0027) reduction in CH4 production over the experiment, declining from 140 g/d during week 1 to 117 g/d in week 8. This inclusion rate of Agolin in the drinking water also resulted in a 25 g (17.6%) CH4/d decrease in emissions by steers compared to control steers (P = 0.0205). However, no significant differences in CH4 yield (g CH4/kg dry matter intake), or CH4 intensity (g CH4/kg LWG) by steers were observed between treatments. These results demonstrated that Agolin reduces CH4 emissions when mixed in an aqueous solution under in vitro and in vivo conditions, providing a potential method to reduce enteric CH4 emissions from cattle in extensive production systems.