33. Effects of Frequency of Asparagopsis Taxiformis Supplementation on Methane Production and Energy and Nitrogen Balance in Beef Steers Fed a Forage-based Diet.

Abstract The objective of this study was to evaluate the frequency of Asparagopsis taxiformis (red seaweed) supplementation and persistence of response on methane (CH4) production and energy and nitrogen balance in cattle. Eight beef steers (267 + 18 kg initial body weight) were randomly allocated into 1 of 2 replicated 4 × 4 Latin squares with 26 d periods. Steers were fed a forage-based diet (68.4% DM, 13.9% CP, 7.1% RDP, 55.9% NDF, 2.13 Mcal/kg ME, 1.54 Mcal/kg NEm, 0.95 Mcal/kg NEg) twice daily (0700 and 1900 h) to 1.8-times calculated maintenance energy requirements and supplemented with pelleted Asparagopsis taxiformis (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. Total fecal and urine collection occurred from d 7 to 10 and d 18 to 21 of each period to determine responses after short- and longer-durations of Asparagopsis supplementation. Similarly, measures of CH4 and CO2 emissions and O2 consumption were collected on d 9 to 10 and d 20 to 21 via open circuit respiration calorimeters. There were no interactive effects of day of measurement and treatment (P > 0.31) for any variable, indicating the response to Asparagopsis persists for at least 21 d. Small reductions in feed refusals resulted in slight increases in measures of dry matter intake (0.12 kg/d; P = 0.02) and gross energy intake (0.49 Mcal/d; P = 0.03) when cattle were provided Asparagopsis vs. control; however, there was no difference for DMI as a percentage of body weight or N intake (P > 0.15). Asparagopsis had no effect (P > 0.12) on fecal energy losses, or digestible energy. Measures of CH4 production were 71.2 g/d (P < 0.01) less than control when steers were provided Asparagopsis at 60 g daily and 120 g every 2 d, which represented an 88% decrease in daily CH4 production. Alternatively, CH4 production when steers were supplemented with Asparagopsis at 60 g every 2 d (80.0 g/d) were similar to control (80.2 g/d; P = 0.96). CH4 energy losses were 0.94 Mcal/d less (P < 0.01) when steers were supplemented Asparagopsis at 60 g daily and 120 g every 2 d, but urinary energy losses were not impacted (P = 0.39). Consequently, measures of metabolizable energy (P < 0.01) and retained energy (P < 0.01) were greater compared to control. Despite these increases in retained energy, this study failed to detect differences (P = 0.32) in measures of N retention. Overall, Asparagopsis taxiformis reduced CH4 production independent of frequency of supplementation when provided at a rate of 60 g/d. Furthermore, decreases in energy losses from CH4 production allowed for greater amounts of metabolizable and retained energy.