Effects of feeding grass silage- and corn silage-based diets in phenotypically low and high methane-emitting...

The objectives of this study were to determine (1) whether replacing grass silage with corn silage reduced methane (CH₄) emissions equally effectively in dairy cows with a low or high CH₄ emission level, (2) whether low or high CH₄-emitting cows remained low and high CH₄ emitters irrespectively of the diet fed, and (3) whether the diet and CH₄ emission level affected lactation performance, feed intake, and rumen microbiome. Emissions of CH₄ of 192 lactating dairy cows were measured with the GreenFeed system (C-Lock Inc.) in a screening phase to select the 12 highest and the 12 lowest CH₄-emitting cows (i.e., 15.9 ± 1.49 vs. 24.0 ± 1.43 g CH₄/kg DMI). These 24 cows were subsequently enrolled in a crossover design trial with a grass silage-based diet (GS) and a corn silage-based diet (CS). The GS diet consisted of 58.0% grass silage, 19.3% corn silage, and 22.7% concentrate, and CS consisted of 19.3% grass silage, 58.0% corn silage, and 22.7% concentrate (DM basis). Treatment periods lasted 4 wk and consisted of a 2-wk adaptation period followed by a 2-wk measurement period. No interaction between diet and CH₄ emission level was observed. Hence, the reduction in CH₄ emissions by CS compared with GS did not differ between the low (-23%) and high (-18%) CH₄-emitting cows. The CH₄ emission level of low-emitting cows was 27% lower than that of high-emitting cows, and was persistent irrespective of the type of diet fed. The community structure and diversity of the rumen microbiome responded to diet and CH₄ emission level, but no interactions were observed except for 1 low-abundance bacterial genus accounting for less than 0.6% of total bacterial relative abundance. Replacing grass silage with corn silage resulted in increased milk yield and DMI, decreased milk fat content and CH₄ emissions, and a shift from acetate to propionate. The latter aligned with the changes in rumen microbiota, shifting from a more fibrolytic, acetate-oriented community with GS toward a more amylolytic, propionate-oriented community with CS. Other than in CH₄ emissions, the low and high CH₄-emitting cows did not differ from each other in feed intake level, lactation performance, and body measures. Despite these similar production responses, low CH₄-emitting cows had distinct ruminal bacterial and archaeal communities compared with high CH₄ emitters across both diets. Low CH₄ emitters were enriched in Succinivibrionaceae_UCG-001, which was positively associated with ruminal molar proportion of propionate. High CH₄ emitters showed higher archaeal diversity and a greater relative abundance of Methanomethylophilaceae. The molar proportions of butyrate and carbon dioxide (CO₂) yield were higher in high-emitting cows compared with low-emitting cows. In conclusion, this study shows that replacing grass silage with corn silage effectively reduces CH₄ emissions regardless of the cow's CH₄ emission level, and that CH₄ emission levels in Holstein-Friesian cows are persistent regardless of diet fed.