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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 the drinking water. Experiment 1 evaluated aqueous solutions of Agolin (50 mg/L) and a non-protein 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, 6% Agolin (w/w) prior to dilution with water at 1.7 mL/L, for a total of five 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 Exp. 2, Droughtmaster steers (n = 24) were fed a basal diet of Rhodes grass hay and were allocated to one of three water treatments (n = 8/treatment) supplemented with either uPRO (2.27 mL uPRO/L water), or one of two 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 Exp. 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 Exp. 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 was observed between treatments. These results demonstrate that Agolin reduces CH4 emissions when mixed in aqueous solution under in vitro and in vivo conditions, providing a potential method to reduce enteric CH4 emissions from cattle in extensive production systems., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

A series of 3 experiments were conducted to evaluate the use of microalgae as supplements for ruminants consuming low-CP tropical grasses. In Exp. 1, the chemical composition and in vitro protein degradability of 9 algae species and 4 protein supplements were determined. In Exp. 2, rumen function and microbial protein (MCP) production were determined in steers fed speargrass hay alone or supplemented with , , , or cottonseed meal (CSM). In Exp. 3, DMI and ADG were determined in steers fed speargrass hay alone or supplemented with increasing amounts of NPN (urea combined with ammonia sulfate), CSM, or . In Exp. 1, the CP content of and (675 and 580 g/kg DM) was highest among the algae species and higher than the other protein supplements evaluated, and sp. had the highest crude lipid (CL) content (198 g/kg DM). In Exp. 2, supplementation increased speargrass hay intake, the efficiency of MCP production, the fractional outflow rate of digesta from the rumen, the concentration of NHN, and the molar proportion of branched-chain fatty acids in the rumen fluid of steers above all other treatments. acceptance by steers was low and this resulted in no significant difference to unsupplemented steers for all parameters measured for this algae supplement. In Exp. 3, ADG linearly increased with increasing supplementary N intake from both and NPN, with no difference between the 2 supplements. In contrast, ADG quadratically increased with increasing supplementary N intake from CSM. It was concluded that and may potentially be used as protein sources for cattle grazing low-CP pastures.