Evaluating the impact of 3-nitrooxypropanol supplementation on enteric methane emissions in pregnant nonlactating dairy cows offered grass silage

Although 3-nitrooxypropanol (3-NOP; Bovaer10) has been proven to reduce enteric methane (CH₄) by ∼30% in indoor systems of dairying when the additive is mixed throughout TMR and partial mixed ration (PMR) diets, there has been limited research to date on the CH₄ abatement potential of 3-NOP when mixed within a diet based on perennial ryegrass silage only and fed to pregnant nonlactating dairy cows. To investigate the effect of 3-NOP supplementation on enteric CH₄ emissions of pregnant nonlactating dairy cows, a 6-wk study was undertaken in which treatment cows were supplemented with 3-NOP mixed within grass silage, whereas control cows were offered grass silage without additive supplementation. Enteric CH₄, hydrogen (H₂), and carbon dioxide (CO₂) were measured using a GreenFeed machine. Body weight, BCS, DMI, and calf birth weight were monitored to determine the effect of 3-NOP supplementation on productivity. The measured dietary concentration of 3-NOP was 63 (range 53.2-77.1) mg/kg DM. Cows supplemented with 3-NOP produced 22% less enteric CH₄ per day and CH₄ per kilogram of DMI, respectively, than cows offered the control diet. Cows supplemented with 3-NOP also produced 4.4-fold more H₂ and H₂ per kilogram of DMI, respectively, relative to the control. The 3-NOP supplementation had no impact on DMI, BW, BCS, or calf birth weight. Supplementing pregnant nonlactating dairy cows with 3-NOP during the winter housing period effectively reduced enteric CH₄ emissions without detriment to productivity.