Effects of different doses of 3-nitrooxypropanol combined with varying forage composition on feed intake, methane emission, and milk production in dairy cows

The objective of this study was to investigate the effect of combining different doses of 3-nitrooxypropanol (3-NOP) with varying forage composition on gas emission and production performance of dairy cows. Seventy-two lactating Danish Holstein cows (36 primiparous and 36 multiparous) were enrolled in a continuous randomized block design with an initial 2-wk covariate period followed by application of treatments for 12 consecutive weeks. Initial DMI and ECM yield were 23.8 ± 3.34 kg/d (mean ± SD) and 38.3 ± 7.12 kg/d, respectively. Cows were blocked according to parity and DIM. Treatments were organized in a 2 × 3 factorial arrangement. The first factor was diet type, reflecting 2 different forage compositions of the diet. The ratio of grass-clover silage to corn silage was 60%:40% of total forage DM in grass-based diets and 40%:60% in corn-based diets. In total, forage constituted 56% of the DM in the partial mixed rations. The second factor reflected 3 doses of 3-NOP: 0, 60, or 80 mg 3-NOP/kg DM. Gas emissions were measured using GreenFeed systems and feed intake by using Insentec Roughage Intake Control bins. Weekly averages from the last 10 wk were analyzed by using a mixed model including fixed effects and interactions among diet type, 3-NOP dose, week, and parity, and included a covariate term and accounted for repeated measures. Methane yield (g/kg DMI) was reduced by 34% and 31%, and CH₄ intensity (g/kg ECM) was reduced by 34% and 32% at 60 and 80 mg 3-NOP/kg DM, respectively, and we found no difference in CH₄ yield or intensity between the 2 doses. The corn- and grass-based diets were similar in NDF and starch levels, and we found no interaction between dose of 3-NOP and diet type for CH₄ yield or intensity. Total DMI was reduced by 9% in cows fed 80 mg 3-NOP/kg DM across diet types, whereas we found no effect on DMI at 60 mg 3-NOP/kg DM. Similarly, ECM yield was reduced by 5% in cows fed 80 mg 3-NOP/kg DM compared with no 3-NOP supplementation, and these cows had a 42% lower BW increase over the experiment compared with no supplementation. In conclusion, 3-NOP at 60 mg/kg DM was efficient in reducing CH₄ without compromising feed intake and milk production, whereas 80 mg 3-NOP/kg DM negatively affected production performance.