Abstract The objective of this study was to evaluate the frequency of Asparagopsis spp. (red seaweed) supplementation on methane (CH4) production in beef cattle fed a forage-based diet. This experiment utilized 8 Angus and Angus-crossbred steers (267 + 18 kg initial body weight) randomly allocated into 1 of 2 replicated 4 × 4 Latin squares with 26 d periods (21 d of experimentation followed by 5 d of rest). Steers were housed in 1.1 × 1.8 m stanchions in a temperature and light controlled room and fed a forage-based diet (66.5% DM, 13.8% CP, 7.0% RDP, 56.3% NDF, 1.54 Mcal/kg NEm) twice daily (0700 and 1900 h) to 1.8-times their estimated maintenance energy requirement. Cattle were supplemented with an Asparagopsis spp. pellet (Brominata, Blue Ocean Barns, Kailua-Kona, HI) at either 0 g (control), 60 g daily, 60 g every 2 d, or 120 g every 2 d. Measures of CH4 and carbon dioxide (CO2) emission and oxygen (O2) consumption were collected on d 9 and 10 and d 20 and 21 of each experimental period by placing the head of each steer into an open circuit respiration calorimeter (91 x 91 x 191 cm) and all respired air was continuously sampled. Production of CH4 and CO2 and consumption of O2 were calculated from differences in concentrations of CH4, CO2, and O2 in respired air and ambient room air, and standardized for temperature, pressure, and humidity. There were no interactive effects of day of measurement and treatment for any variables (P 0.50). Supplementation of Asparagopsis spp. had no effect on dry matter intake (DMI; P = 0.37). Measures of CH4 production were 56.0 g/d less (P 0.01) than control when steers were provided Asparagopsis spp. at 60 g daily and 120 g every other day. Alternatively, CH4 production when steers were supplemented with Asparagopsis spp. at 60 g every 2 d (71.15 g/d) were similar to control (75.50 g/d; P = 0.59). Measures of CH4 yield (g d-1/kg DMI; P 0.01) or intensity (g d-1/kg BW0.738; P 0.01) followed measures of CH4 production. Interestingly, Asparagopsis spp. increased CO2 production by 188.6 g/d compared to the control (P 0.01), which was independent of frequency or amount of supplementation. Overall, Asparagopsis spp. supplementation reduced CH4 production, yield and intensity independent of frequency of supplementation, as long as Aparagopsis spp. supplementation was provided at a rate of 60 g/d.
Talley et al. (2026) studied this question.