Assessing future economic and environmental impacts of selecting resilient dairy cows using integrated mechanistic and genetic modelling

Breeding for more resilient cows may help the global dairy industry to adapt to future climate change. However, the performance of selected cows in future environments cannot be directly assessed from historical data. Therefore, this study aimed to simulate the phenotypic performance and to assess the economic and environmental impacts of selected cows in future environments (year 2055) by integrating mechanistic and breeding simulation models. Longitudinal phenotypic trajectories were simulated for populations of 20 000 dairy cows. Future climatic conditions were simulated by increasing the ambient temperature by 0.7 ℃ every ten years. Investigated traits included average daily milk yield (DMY), average daily dry matter intake (DDMI), interval from calving to conception (ICC), milk loss, log-transformed variance of milk deviations (LnVar), and lactation efficiency. Two balanced breeding goals were designed, with one prioritising production and the other resilience. Phenotypic performances of 20 000 future cows were simulated by updating key parameters of mechanistic models to reflect correlated genetic responses over 30 years of selection. The economic and environmental impacts of future populations were obtained by integrating a bio-economic model and lifecycle assessment. The results of lifetime performances of cows in 2055 indicated that cows selected with the breeding goal prioritising resilience would produce less milk (7.4-10.3 kg per day), consume less feed (2.6-5.8 kg DM per day), conceive earlier (5.9-12.3 days), are culled later, and become more resilient (lower phenotypic values for milk loss and LnVar) and less efficient (lower phenotypic values for lactation efficiency) compared to cows selected with the breeding goal prioritising production. The results of economic and environmental analyses indicated that cows selected for resilience could generate a higher lifetime profitability (though a lower profit per cow per year is observed) and could emit less greenhouse gases per year than cows selected for production. In conclusion, this study showed that resilient cows would benefit both lifetime profitability per cow and environmental sustainability under climate change conditions, providing solid and positive evidence for selecting for resilience in dairy cattle breeding.