Evaluation of Seaweed-Based Feed Additive on Enteric Methane Emissions of Grazing Heifers

This study evaluated the impact of a seaweed-based feed additive (SBFA) on enteric methane emissions in grazing heifers. Two groups of heifers (<i>n</i> = 11 per group) were maintained on tame pasture under identical conditions. The trial consisted of three phases: a two-week baseline period, a two-week adaptation period, and a seven-week full-dose period. During adaptation, the treatment group received SBFA once daily, with the dosage gradually increased to a target dose of 280 mg bromoform/head per day. This full dose was administered throughout the final phase. Enteric emissions of methane were continuously monitored using the GreenFeed emission monitoring system. During the baseline period, gas emissions were not different between the groups (<i>p</i> = 0.75); however, during the adaptation (<i>p</i> = 0.08) it tended to be lower in the SBFA group compared to the control, and during the full-dose period, methane emissions in the SBFA treatment group were significantly (<i>p</i> < 0.01) lower than in the control group (<i>p</i> < 0.01), averaging 53.7 g/d versus 203.2 g/d, corresponding to a 73.6% reduction in methane. Additionally, a prolonged suppression effect was observed, with methane emissions in the treatment group remaining low for three days after removal of the SBFA compared to the control group (<i>p</i> < 0.01), and on day 4 after the removal, the SBFA treatment group still tended (<i>p</i> = 0.07) to be lower than the control group. These findings indicate that SBFA, when administered once daily, has significant potential for mitigating enteric methane emissions in grazing cattle.