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The effects of supplementing high- or low-concentrate diets with sunflower oil (SO) on rumen fermentation, nutrient utilization, and ruminal methane (CH 4 ) emissions in lactating cows were examined. Four multiparous Nordic Red dairy cows fitted with rumen cannulae were used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments and 35-d periods. Experimental treatments comprised iso-nitrogenous total mixed rations based on grass silage with forage to concentrate ratio of 65:35 or 35:65 supplemented with 0 or 50 g/kg diet DM of SO. Apparent ruminal OM and starch digestibility was greater ( P &lt; 0.05) with high- than low-concentrate diets but was unaffected by SO. Inclusion of SO in high-concentrate diet decreased ( P ≤ 0.05) apparent total tract OM, fiber, and GE, and apparent ruminal fiber digestibility. High-concentrate diets and SO shifted ( P &lt; 0.05) fiber digestion from rumen to the hindgut. High-concentrate diet resulted in a lower rumen pH and elevated total rumen VFA concentration compared with low-concentrate diet, whereas SO increased rumen pH and decreased rumen VFA concentration when included in high-, but not low-concentrate diet ( P &lt; 0.05 for interaction). High-concentrate diet reduced rumen ammonia-N ( P &lt; 0.01) and molar proportion of acetate to propionate ( P &lt; 0.01), and decreased ( P &lt; 0.05) ruminal CH 4 emissions when expressed as g/d or g/kg OM digested in the rumen. With both low- and high-concentrate diets, SO reduced ( P &lt; 0.05) daily emissions of CH 4 as g/d or g/kg OM digested in the rumen, but SO reduced CH 4 emissions expressed as g/kg OM intake, OM digested in total digestive tract, energy-corrected milk or % of GE intake only with low-concentrate diet ( P ≤ 0.05 for interaction). In conclusion, replacing grass silage with concentrates led to a reduction in daily ruminal CH 4 emissions that were accompanied by a shift in rumen fermentation toward the synthesis of propionate, and decreases in rumen pH and fiber digestion. Sunflower oil was effective in reducing daily CH 4 emissions in lactating cows which was accompanied by a noticeable lower feed intake with high- but not low-concentrate diet. Overall the effects of SO and greater proportion of concentrates in the diet on daily CH 4 emissions were additive but the additivity declined or vanished when different indices of CH 4 emission intensity were considered. Consequently, SO was more effective in reducing CH 4 emissions when low-concentrate diet was fed.

translational animal science

Dietary forage to concentrate ratio and sunflower oil supplement alter rumen fermentation, ruminal methane emissions, and nutrient utilization in lactating cows1