Investigating the effect of 3-nitrooxypropanol on milk production and enteric methane emissions of autumn-calving dairy cows fed a perennial ryegrass silage, corn silage, and concentrate diet.

The objective of this experiment was to investigate the effect of 3-nitrooxypropanol (3-NOP) supplementation on the milk production and enteric methane (CH4) emissions of Irish autumn-calving dairy cows fed a perennial ryegrass silage, corn silage and concentrate diet indoors. The experiment consisted of a 2-wk covariate period followed by a 6-wk period of data collection during which cows were housed in a free-stall barn. Twenty-four primiparous (mean ± SD; 74 ± 13 DIM and 498 ± 30 kg of BW) and 64 multiparous (60 ± 21 DIM and 611 ± 45 kg of BW) autumn-calving dairy cows were blocked based on pre-experimental milk solids (MSo) production, BW, parity and CH4 production (g/d) and were then randomly assigned to one of 2 treatments. The 2 treatments were; 1) a diet not supplemented with 3-NOP (CTL); and 2) a diet containing 71.8 mg of 3-NOP/kg DM (3-NOP). Milk production was recorded daily and milk composition, BW and BCS were measured weekly. Enteric CH4, hydrogen (H2) and carbon dioxide (CO2) were measured using the GreenFeed technology. Cows fed 3-NOP had similar milk yield when compared with cows fed CTL; however, cows fed 3-NOP tended to have greater fat and protein corrected milk (FPCM) yield and energy corrected milk (ECM) yield when compared with cows fed CTL. Cows fed 3-NOP had greater milk protein concentration, milk protein yield and MSo yield when compared with cows fed CTL. Milk fat concentration and milk fat yield were not affected by 3-NOP treatment; however, cows fed 3-NOP had greater proportions of de novo fatty acids (FA) and lower proportions of preformed FA when compared with cows fed CTL. Cows fed 3-NOP had 26% lower CH4 production and 4 times greater H2 production when compared with cows fed CTL. Cows fed 3-NOP had 28% lower CH4 yield (g CH4 per kg of DMI) when compared with cows fed CTL, as well as 27% lower CH4 intensity (g CH4/kg MSo, g CH4/kg ECM and g CH4/kg FPCM). In conclusion, supplementation with 3-NOP reduced CH4 emissions in autumn-calved dairy cows fed a forage-concentrate diet indoors, without negatively affecting animal performance. Due to challenges associated with administering 3-NOP to grazing cows, further research is required to develop CH4 mitigation strategies that are effective during the grazing season and complement the reductions achieved with 3-NOP during the indoor feeding period in Irish autumn-calving systems.