Effect of the nature of energy (lipids vs. carbohydrates) on enteric methane emission and dairy performance in cows fed grass silage-based diets

This work aimed to investigate the effect of energy nature (lipids vs. carbohydrates) on enteric methane emission (eCH4 ) and performance in dairy cows fed grass silage-based diets. Eight multiparous Holstein cows were used in a 4 x 4 Latin square design, with 4 experimental periods of 28 days each. Cows were fed with 4 iso-energetic diets based on grass silage and supplemented with different levels of rapeseed oil (RO) (0, 1.5, 3.0, 4.5% of dietary dry matter (DM), Control, RO-low, RO-medium, RO-high diets, respectively) in substitution of starch from concentrate. Dairy performance, total-tract digestibility, and rumen parameters were measured when animals were in individual respiration chambers for quantifying eCH4. Intake of DM decreased with RO-high compared to other diets. Methane emissions were lowered similarly with all diets containing RO compared to Control (on average, -19% in g/d, -13% in g/kg DMI, -21% in g/kg milk). Ruminal propionate proportion was higher, whereas that of butyrate was lower with RO-high compared to the other diets. Milk yield was higher with RO-low and RO-medium, and was lower for RO-high compared to Control. Milk C16:0 concentration was lower, and C18:1c9, C18:1t11, and other rumen biohydrogenation intermediate concentrations were higher with diets containing RO compared to Control. The shift from the C18:1t11 to C18:1t10 biohydrogenation pathway is in agreement with the milk fat depression observed with RO-medium and RO-high. The inclusion of RO at 1.5% was the best compromise between eCH4, feed efficiency, and milk nutritional quality in cows fed grass silage-based diets. Energy substitution of carbohydrate (mainly starch) by rapeseed oil reduced methane emissions in dairy cows fed grass silage-based diets (up to -23% in g/d) Rapeseed oil content above 3% induced milk fat depression and impaired milk fatty acid profile The inclusion of 1.5% rapeseed oil was the best compromise to reduce methanogenesis (-15% in g/d) and improve dairy performance and milk nutritional quality

Automated summary

This study aimed to investigate the effect of energy nature on enteric methane emission and performance in dairy cows. The results showed that substituting carbohydrates with rapeseed oil reduced methane emissions and improved dairy performance.