294 Pelleted seaweed (Asparagopsis taxiformis) effectively reduces enteric methane emissions in grazing beef cattle.

Abstract The ruminant livestock sector contributes to global greenhouse gas emissions. Thus, there is a need to develop novel mitigation strategies, especially for pasture-based systems as less than half of the identified strategies are applicable to grazing systems. This study aimed to examine the use of pelleted bromoform-containing seaweed (Asparagopsis taxiformis) marketed as Brominata, as an enteric methane (CH4) inhibitor in grazing beef cattle under real-world farm conditions. The study was conducted at the Selkirk division of Matador Ranch and Cattle in Dillon, Montana, USA, situated in a semi-arid climate with cold, dry winters and hot, wet summers. Twenty-four crossbred Wagyu-Angus beef steers, with an average liveweight of 399 ± 21.7 kg, were allocated to two treatment groups: Control and Brominata. Measurements of CH4, carbon dioxide (CO2), and hydrogen (H2) emissions were conducted using the GreenFeed system which also was used to administer the pelleted supplements. The control group received a pellet composed of 65% wheat mids, 15% molasses, and 20% bentonite (CHS Nutrition, Great Falls, Montana, USA). The Brominata group received a pellet containing Brominata (20%, Blue Ocean Barns, Kailua Kona, HI, USA), distillery solubles (15%), wheat mids (65%), a palatability enhancer (Inhace, 0.25%, Qualitech, Chaska, Minnesota, USA), molasses coating, and wheat mids dusting. The bromoform concentration in the pellets was 1.4 mg g/dry matter. The study was conducted in an intensive irrigated pasture, where the steers remained together throughout the experiment. Central pivot irrigation and rotational grazing management were used with a fixed stocking rate. Statistical analysis was conducted using SAS 9.4, with a model incorporating fixed effects for treatment, time, their interaction, and a covariate, while accounting for animal variations as a random effect within each phase. Three phases of bromoform intake were identified: a 3-week ramp-up phase, a 3-week optimal phase, and a 2-week decreasing phase. No differences were observed between the groups in terms of weekly initial and final liveweight, average daily gain, or predicted dry matter intake. However, during the optimal and decreasing phases, average enteric CH4 emissions were significantly (P < 0.05) reduced in steers that received Brominata supplementation compared to the Control (115 vs. 185 g/d, respectively). CO2 emissions were similar between the two groups (6.8 vs. 7.2 kg/d), while H2 emissions were lower (P < 0.05) in the control group (3.4 vs. 1.8 g/d). The findings suggest that pelleted bromoform-containing feed additive has the potential to reduce enteric CH4 emissions from grazing beef cattle. The observed 37.7% average reduction in CH₄ production, achieved without compromising animal performance, suggests a promising approach for mitigating the environmental impact of livestock farming.