The effect of twice daily 3-nitroxypropanol supplementation on enteric methane emissions in grazing dairy cows

Although 3-nitroxypropanol (3-NOP) has been proven to reduce enteric methane (CH₄) by ∼30% in indoor systems of dairying when the additive is mixed throughout a TMR, very limited research has been done to date in grazing systems in which the most convenient method of additive supplementation is at milking twice daily. To investigate the effect of twice daily 3-NOP supplementation on enteric CH₄ emissions, a 12-wk study was undertaken in which treatment cows (n = 26) were supplemented with 3-NOP (80 mg/kg DMI) twice daily at morning and evening milking, and control cows (n = 26) received no additive supplementation. Enteric CH₄, hydrogen (H₂) and carbon dioxide (CO₂) were measured using GreenFeed units, and milk production, BW, BCS, and DMI were monitored to determine the effect of 3-NOP supplementation on productivity. No significant effect was observed for 3-NOP supplementation on any of the aforementioned parameters with the exception of CH₄ and H₂ production, respectively. Cows supplemented with 3-NOP produced 1.6-fold more H₂ (P < 0.001) across a 24-h period, with reductions in CH₄ production of 28.5% recorded in the 3 h after additive consumption (P < 0.001), however, levels of CH₄ production returned to that of the control group thereafter. When CH₄ production was considered across the entire 24-h period, the cows offered 3-NOP produced ∼5% less CH₄ than the control (P < 0.050). Future research should focus on methods to increase the efficacy of the additive throughout the day which would include the deployment of a slow-release form or an out-of-parlor feeding system that allows animals consume the product at additional time points.