Implications of dietary interventions (forage to concentrate ratio and forage type) in high or low methane-emitting dairy cows: Nutrient digestibility, rumen fermentation, and energy and nitrogen utilization

Following the measurement of methane (CH4) emissions from 100 Nordic Red lactating dairy cows, a subset of 10 cows was selected based on CH4 yield (g CH4/kg DM intake) being low (Low emitter = 22.9 ± 1.1; n = 5) or high (High emitter = 24.0 ± 0.9; n = 5) emitters to evaluate the relationship between CH4 yield phenotypes and experimental diets [forage to concentrate (FC) ratio and forage type] on enteric CH4 production, feed intake, lactation performance, ruminal digestion and passage kinetics, digestibility, and energy and nitrogen utilization. Ten lactating dairy cows fitted with rumen cannula were randomly allocated to experimental diets in a 3 times replicated 3 × 3 Latin square with an extra replicate that was randomly allocated to one of the diets in each 35-d experimental period, resulting in n = 10 for each diet. The experiment was split into 2 blocks (blocks A and B) of 4 or 6 cows over time (7-wk interval) to have all cows in the same lactation stage. Dietary treatments comprised grass silage-based diets containing high (70:30, HG) or low (30:70, LG) FC ratio or a red clover silage-based diet with FC ratio of 50:50 (RC) on DM basis. Intakes of DM and gross energy (GE) for cows fed LG were greater than HG and RC in both cow groups whereas NDF intake was lower for LG and RC than HG and no interaction was detected. Milk yield was 12% greater for LG and RC than HG, but ECM yield was the greatest for LG. The diets clearly affected all the rumen fermentation parameters while only propionate and butyrate proportions, and NH3-N concentration were affected by the interaction; Low-emitting cows had greater ruminal propionate and lower butyrate proportions than High-emitting cows on LG and High-emitters had the highest NH3-N concentration with RC. In addition, CH4 intensity (g CH4/kg milk) was greater for LG in Low- than High-emitting cows. Total-tract digestibility of DM, OM, and GE was greater for LG and HG relative to RC without any interaction effect and High-emitters had greater nutrient digestibility compared with Low-emitters. Diets but not cow group affected rumen contents and ruminal digestion and passage kinetics without any interaction whereas cows fed LG had shorter DM mean retention time than HG and RC. Feeding LG improved energy balance and affected other parameters of energy utilization whereas cow group and interaction effects were not significant. Overall, there were clear differences with respect to CH4 yield phenotype on nutrients digestion and energy or N utilization in Low- vs. High-emitters whereas dietary treatments affected lactation performance, digestion, rumen fermentation and kinetics, and energy utilization of dairy cows. These findings indicate that dairy cows with low CH4 yield may experience negative consequences on nutrient digestibility.