Herd management strategies for greenhouse gas emission mitigation in dairy production: A simulation study

General dairy herd management can be tailored to dilute enteric methane and total farm GHG emissions per kilogram of milk delivered and thereby serve as a mitigation strategy. However, there is limited information on the performance of different herd management strategies in dairy herds with varying productivity and the trade-offs between emission mitigation, farm economy, and dairy food production. Here, we simulated a set of herd management strategies in 10 high-yielding Danish conventional Holstein herds using herd simulation modeling and a cradle-to-farm gate partial life cycle assessment to estimate the effects on GHG emission, gross margin, and edible protein yield, and the trade-offs between these effects. These strategies included increased concentrate intake, improved reproduction, reduced risk of health problems, and extended lactation. The simulation was conducted by changing relevant parameters within certain targets according to Danish national figures for conventional Holstein herds. Results showed that the herd management strategies changed GHG emissions from a slight increase of 0.4% to a decrease of up to 3.2% on average across the 10 herds. These strategies also changed the gross margin from -2.2% to +5.0% across herds. The herds' edible protein yield increased except for a slight decrease in the strategies with improved reproduction or extended lactation. Overall, the effects of the strategies varied between herds. We did not detect any obvious trade-off between emission mitigation and gross margin. These findings revealed that tailored herd management can benefit emission mitigation and gross margin while generally maintaining edible protein production; however, the effects depend on the herds' initial management and productivity.