Effect of 3-nitrooxypropanol supplementation combined with 6-hour grazing on enteric methane emissions and milk production characteristics.

As a methane-reducing feed additive, Bovaer or 3-nitrooxypropanol (3-NOP) is one of the most extensively researched additives. Numerous studies have demonstrated the efficacy of 3-NOP in reducing methane emissions. However, its practical implementation on commercial farms may be challenging due to varying farm management practices and circumstances, as using feed additives in pasture-based systems present numerous challenges. One area of uncertainty is the impact of restricted grazing on the effectiveness of 3-NOP in reducing methane emissions. For optimal effectiveness, 3-NOP should be administered consistently throughout the day via frequent intake of a partially mixed ration (PMR), TMR, or concentrate. This approach aligns with its mode of action, as 3-NOP is metabolized under the anaerobic conditions of the rumen. Consistent exposure to 3-NOP is not feasible when cows spend part of their day grazing on pasture without access to feed containing 3-NOP. Therefore, methane reductions observed in TMR-fed cows should not be directly extrapolated to grazing animals, and information is needed to establish whether methane reduction can be maintained when 3-NOP administration via PMR is combined with restricted grazing. This was the main objective of the study cited.

A Latin square design with 40 lactating Holstein-Friesian cows (average milk yield of 39.8 ± 7.0 kg/d per cow, mean BW 691 ± 63.6 kg, average lactation stage of 122 ± 56 DIM, and a mean lactation number of 2.6 ± 1.2) was set up including three treatment periods and four treatments. The treatments consisted of full-time indoor housing with a placebo additive (A), full-time indoor housing with 80 mg 3-NOP per kg DMI (B), 6-hour grazing with a placebo additive (C), and 6-hour grazing with 80 mg 3-NOP per kg DMI (D). The actual 3-NOP concentration in the total diet was 77 mg per kg in treatment B and 80 mg per kg in treatment D. Animal performance, fresh grass intake, methane emissions (GreenFeed system), and nutritional value of the feed were monitored throughout the experiment.

The results showed that DMI was not different between treatments with the same housing conditions, but was significantly lower (−1.4 kg DM per day) for 6-hour grazing compared with full-time indoor housing. The milk yield of grazing treatments was significantly lower (−1.6 kg per day) than full-time housed cows receiving the placebo, whereas the milk yield of full-time housed cows receiving 3-NOP was not different from the full-time housed placebo treatment, nor the grazing placebo treatment. However, fat- and protein-corrected milk yield was significantly lower in grazing treatments compared with full-time housed treatments, with −2.57 kg per day for 3-NOP treated cows and −2.03 kg per day for placebo treated cows. The absolute CH4 emission was lower in grazing treatments (−7.2% for placebo and −12.3% for 3-NOP) compared with full-time housed treatments with similar additive treatments, but clearly lower in 3-NOP treatments versus placebo treatments (−25.1% in no grazing and −29.2% in 6-hour grazing treatments).

It was concluded that it was possible to obtain a significant methane emission reduction of 34.3% by combining restricted 6-hour grazing with 3-NOP supplementation in the PMR when using a dose of 80 mg 3-NOP per kg total DMI compared with full-time indoor-housed cows. Although milk production was significantly lower in grazing treatments, methane intensity (g CH4 per kg FPCM) was still 28.5% lower than in non-grazing cows when 3-NOP was supplemented.