Investigating Supplementation with Asparagopsis taxiformis in Mineral to Reduce Enteric Methane from Grazing Cattle

While methane emissions from cattle contribute to greenhouse gases, supplementing with red seaweed Asparagopsis taxiformis (AT) demonstrates an up to 90% methane reduction in controlled feeding studies. However, methods for delivery of AT in grazing systems remain unexplored. This study evaluated AT with mineral supplementation to 112 weaned steers grazing on annual rangeland over 157 days. Cattle were randomly assigned to access mineral with freeze-dried AT (targeting 150 mg bromoform/head/day) or mineral without AT. Methane emissions were measured using laser methane detection (LMD) and body weight, mineral consumption, and blood selenium levels were monitored. Average daily mineral consumption was lower than targeted, resulting in suboptimal bromoform intake (89.2 mg/head/day). No significant differences were observed between treatments for mineral consumption, weight gain, or blood selenium levels. Cattle with access to mineral with AT had lower peak emissions than control cattle when measured at day 25, but no differences in peak emissions were measured at day 115 or day 157. The lack of methane reduction was attributed to insufficient bromoform dosing, potential compound degradationduring field storage, and limitations of laser methane detection. Achieving consistent dosing and accurate methane assessment in extensive grazing systems requires improved delivery mechanisms, compound stabilization, and measurement techniques.