3-Nitrooxypropanol decreases methane emissions and increases hydrogen emissions of early lactation dairy cows, with associated changes in nutrient digestibility and energy metabolism.

Enteric methane is to varying degrees an end product of microbial fermentation in the rumen and hindgut of ruminant livestock. Because it is a potent greenhouse gas (GHG) that contributes to global warming, enteric methane has become one of the main targets of GHG mitigation practices in the dairy industry. Several dietary strategies may contribute to mitigating enteric methane production, including the use of feed additives. Some feed additives, which can be natural or synthetic compounds, are inhibitors of methanogenesis. One such feed additive is 3-nitrooxypropanol (3-NOP). The compound 3-NOP is a highly specific inhibitor that targets an enzyme which catalyzes the final step in methanogenesis. At low concentrations, 3-NOP appears to inhibit methanogens without having a negative effect on performance in dairy cattle. Hence, 3-NOP seems to be an effective feed additive to mitigate methane emission in dairy cows. The aim of the study by Dr S van Gastelen and colleagues was to build on this finding by determining the methane mitigation potential of 3-NOP and its persistency in lactating cows, as well as its effects on feed intake of the cows, energy and N balance, milk production and composition, milk fatty acid profile, and hydrogen emissions. The results of the study were published in the Journal of Dairy Science volume 103 of 2020, page 8074 to 8093. The title of the paper is: 3-Nitrooxypropanol decreases methane emissions and increases hydrogen emissions of early lactation dairy cows, with associated changes in nutrient digestibility and energy metabolism.

Sixteen Holstein-Friesian cows (11 cows in their second lactation and 5 cows in their third lactation) were blocked in pairs, based on actual calving date, lactation number and previous lactation milk yield, and randomly allocated to one of two dietary treatments: a diet including 51 mg of 3-nitrooxypropanol per kg of dry matter (3-NOP) and a diet including a placebo at the same concentration (CON). Cows were fed 35% grass silage, 25% maize silage and 40% concentrate (dry matter basis) from three days after calving up to 115 days in milk (DIM). Every four weeks, the cows were housed in climate respiration chambers for 5 days to measure lactation performance, feed and nutrient intake, apparent total-tract digestibility of nutrients, energy and N metabolism, and gaseous exchange (4 chamber visits per cow in total, representing 27, 55, 83, and 111 DIM).                                                                                        

The results showed that feeding 3-NOP did not affect dry matter intake (DMI), milk yield, milk component yield, or feed efficiency. These variables were affected by stage of lactation, following the expected pattern of advanced lactation. Feeding 3-NOP also did not affect methane production (g per day) at 27 and 83 DIM, but decreased methane production at 55 and 111 DIM by an average of 18.5%. This response in methane production is most likely due to the differences observed in feed intake across the different stages of lactation because methane yield (g per kg of DMI) was on average 16% lower at each stage of lactation upon feeding 3-NOP. On average, feeding 3-NOP increased hydrogen production and intensity 12-fold. With the CON treatment, hydrogen yield did not differ between the different stages of lactation, whereas with the 3-NOP treatment hydrogen yield decreased from 0.429 g per kg of DMI at 27 DIM to 0.387 g per kg of DMI at 111 DIM. The apparent total-tract digestibility of dry matter, organic matter, neutral detergent fibre, and gross energy was greater for the 3-NOP treatment. In comparison to CON, 3-NOP did not affect energy and N balance, except for a greater metabolizable energy to gross energy intake ratio (65.4 and 63.7%, respectively) and a greater body weight gain (average 0.90 and 0.01% body weight change, respectively).

In conclusion, the results showed that feeding 3-NOP could be effective in decreasing methane emissions, while at the same time increasing hydrogen emissions, in early lactation Holstein-Friesian cows. It could also be positive to apparent total-tract digestibility of nutrients.