B16 GxE interactions for enteric methane emissions of dairy cows (BO-43.10-002-058)

There are currently two mitigation strategies available in practice to lower the enteric methane emissions of dairy cattle: (1) breeding for lower emitting cows, and (2) applying dietary strategies. Many questions arise if and how these two mitigation strategies interact, as this is also important to know for life cycle assessments and the credit systems for low(er) carbon footprints. Are the reduction effects of both strategies additive (i.e., the combined effect is equal to the sum of the individual effects), antagonistic (i.e., the combined effect is less than the sum of the individual effects), or synergistic (i.e., the combined effect is greater than the sum of the individual effects)? Can, for example, the reduction effects of Bovaer (20-30%) and breeding (1% per year) simply be added up? And does the exchange of grass silage with corn silage have the same reduction effect on high genetic merit cows, as on low genetic merit cows? This is what is called G(enotype)xE(nvironment) interaction, also known as environmental sensitivity of genetic merit. It describes the phenomenon that different genotypes respond differently to changes in the environment; a dietary strategy in this case.

There is historic data available in the Netherlands where enteric methane emission was recorded of dairy cows fed a large variety of diets (i.e., different methane mitigating dietary strategies). These data include sniffer-data from the Climate Smart Cattle Breeding project and GreenFeed-data of multiple trials at the Dairy Campus. In April 2025, the methane breeding values were launched in the Netherlands and we therefore also have a first estimate of the genetic merit of these cows in the historic dataset. The first and most important activity of this project is to analyze the historic data to explore whether indications for GxE interactions exist. Since no dedicated trial was set up to investigate GxE interactions, it can be expected that this exploration results in indications and not in definite conclusions.