Lactational performance and enteric methane emissions in dairy cows fed high-oil oats, cold-pressed rapeseed cake, and 3-nitrooxypropanol in a grass silage-based diet.

The objective of this study was to evaluate the effects of high-oil oats and cold-pressed rapeseed cake (RSC) as dietary ingredients, along with supplementation of 3-nitrooxypropanol (3-NOP), on apparent total-tract digestibility, milk production, and enteric CH₄ emissions in dairy cows fed a grass silage-based diet. Twenty-four lactating Nordic Red cows were grouped into 3 blocks. The experiment was conducted as a cyclic change-over where each treatment had 3 observations per period. The experiment consisted of 4 periods of 28 d each, including 18 d of diet adaptation and 10 d of data and sample collection. The 2 × 2 × 2 factorial design included 2 energy sources (barley or high-oil oats), 2 protein supplements (rapeseed meal [RSM] or RSC), and 3-NOP supplementation at 2 levels (0 or 68 mg/kg of DM), resulting in 8 dietary treatments. The basal diet consisted of 60% grass silage (on a DM basis). Inclusion rates of the experimental concentrates were 27% to 29% and 29% to 31% for barley and high-oil oats, respectively, and 8% to 10% and 10% to 12% for RSM and RSC, respectively. Diets were offered ad libitum as a TMR. Daily DMI, milk yield, BW, and gas emissions were recorded throughout the experiment. Gas emissions were measured using the GreenFeed system. Ether extract (EE) content across experimental diets ranged from 2.9% to 6.1% of DM. Total DMI tended to increase with high-oil oats compared with barley, but decreased with RSC compared with RSM. Digestibility of DM, OM, NDF, and EE decreased with high-oil oats versus barley, and EE digestibility increased with RSC versus RSM. Despite lower nutrient digestibility, milk and ECM yield increased by 2.4 kg/d with high-oil oats compared with barley. Milk yield decreased by 1.1 kg/d and ECM yield tended to decrease by 1.0 kg/d with 3-NOP supplementation. Milk protein concentration decreased with high-oil oats versus barley and with RSC versus RSM. Feed efficiency increased with high-oil oats compared with barley. Daily CH₄ emissions (g/d), CH₄ yield (g/kg of DMI), and CH₄ intensity (g/kg of ECM) decreased by 11.2%, 14.2%, and 15.3%, respectively, when barley was replaced with high-oil oats in combination with RSM but were not affected in combination with RSC. Daily CH₄ emissions, CH₄ yield, and CH₄ intensity decreased by 12.5%, 10.6%, and 12.7%, respectively, when RSM was replaced with RSC in combination with barley but not in combination with high-oil oats. Daily CH₄ emissions, CH₄ yield, and CH₄ intensity decreased by 33.5%, 30.9%, and 31.2%, respectively, with 3-NOP supplementation, with slightly greater efficacy on CH₄ intensity when barley was used as the energy source. Urinary urea concentration was greater with high-oil oats than with barley, and lower with RSC than with RSM, but only in combination with high-oil oats. In conclusion, both high-oil oats and RSC are practical dietary ingredients for reducing enteric CH₄ emissions and CH₄ intensity. High-oil oats may additionally improve feed efficiency and production performance in dairy cows. Supplementation with 3-NOP reduced enteric CH₄ emissions by more than 30% with additive effects when combined with RSC, but negatively affected production performance.