The objectives of this project were to measure the effect of SeaFeed, a canola oil infused with Asparagopsis armata, on methane emissions, animal health, performance, and carcass characteristics of feedlot cattle. Angus steers (n = 160) with an initial body weight of 474.4 kg were fed a steam-flaked wheat and barley ration for 200 d in a large, commercial feedlot. A single-blinded randomized complete block design compared two treatments including control and SeaFeed included at a rate of 25 mg bromoform per kg dry matter intake (DMI). Monthly testing of bromoform levels in the canola demonstrated that SeaFeed maintained a stable bromoform concentration for 6 mo. The inclusion of SeaFeed had no effect on daily DMI. However, steers fed SeaFeed were more efficient with a 6.6% higher (P < 0.01) gain-to-feed ratio as compared to control steers over the 200-d feeding period. This improved efficiency resulted in 0.094 kg higher (P < 0.01) average daily gain and 19.7 kg higher (P < 0.01) live exit weight in steers fed SeaFeed as compared to control steers. Steers fed SeaFeed produced 51.7% less (P < 0.01) methane and yielded 50.5% less (P < 0.01) methane over the 200-d feeding period as compared to cattle fed the control ration. Peak methane inhibition occurred on day 29 on feed with 90.6% less methane production in cattle fed SeaFeed as compared to control animals. SeaFeed reduced (P < 0.01) methane intensity by 55.4% over the 200-d feeding period. Hot carcass weight tended (P = 0.097) to be 6.9 kg heavier in cattle fed SeaFeed as compared to controls. Cattle fed SeaFeed had similar (P > 0.20) marbling, meat color, eye muscle, area, and ultimate pH to control cattle. Interestingly, cattle fed SeaFeed tended (P = 0.054) to have slightly higher fat color scores. Rumen papillae from cattle fed SeaFeed were more (P < 0.01) gray in color and more oval (P < 0.01) in shape as compared to control animals; however, rumen damage was not different between treatment groups. In regards to food safety and residues, all muscle, fat, and kidney samples were free from bromoform residues. Bromine residues in kidney and meat samples were higher (P < 0.01) in the SeaFeed group as compared to controls. Cattle fed SeaFeed produced strip loin steaks similar (P > 0.05) in eating quality to control cattle. These results demonstrate that SeaFeed reduced methane emissions, improved performance, and produced safe beef with similar eating quality to conventional beef.

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