The effect of bromoform supplementation in Angus cows during late gestation on offspring’s growth performance and maternal greenhouse gas emissions using two devices

Asparagopsis taxiformis and Asparagopsis armata are red seaweed species capable of reducing enteric methane (CH₄) emissions in cattle by over 80 % due to the presence of bromoform. This project aimed to investigate the effect of bromoform supplementation on CH₄ emissions of pregnant cows fed low-quality feed and its impact on growth performance of offspring. Gas measurements were obtained using both a handheld device (Bosean K-600) and GreenFeed units. Forty-two pregnant Angus cows (706 ± 71 kg; mean ± standard deviation) were allocated to a control or bromoform group based on body weight. The bromoform group was supplemented with bromoform (0.69 $\pm$ 0.07 mg/kg body weight/day) pre-calving. Progeny weights at birth and 156 days of age were recorded. Calf growth was not affected by the treatment. There was an interaction between treatment and duration of supplementation for CH₄ emissions (P = 0.0015). Bromoform supplementation decreased cow CH₄ emissions by 45 % in the first week, 70 % in the second week, and 77 % in the third and fourth weeks. No difference was observed for CH₄ emissions between weeks 1 to 4 for the control group. Carbon monoxide levels (ppm) were significantly higher in the bromoform group (0.39 vs 33.54 ppm; P = 0.0158). Moderate to high correlations were observed between devices for CH₄ emissions. Maternal bromoform supplementation effectively mitigates CH₄ while not impacting the progeny body weights in beef cattle. The correlations between devices demonstrated potential for future adoption of the handheld device.