Interaction between adaptation and mitigation traits in Canadian Holsteins
Abstract
In response to climate change, the dairy industry has shifted focus to reducing environmental impact and strengthening resilience. However, it is unclear how adaptation to environmental challenges and mitigation of environmental effects interact. This project aims to quantify the impact of selecting traits related to adaptation on profitability, health, efficiency, resilience, and environmental sustainability to inform selection of climate-smart dairy. Mitigation traits were defined as methane production (g/d), body maintenance requirements, and dry matter intake while adaptation traits were defined as heat tolerance with regards to production, fertility, and health. The first objective will be to quantify the direct effects of heat stress on production, fertility, health, and mitigation traits using a reaction norm approach to estimate heat tolerance. The second objective will be to estimate genetic correlations between mitigation traits and heat tolerance defined by production, fertility, and health traits. The third objective is to estimate genetic correlations among heat tolerance defined by all trait groups. Preliminary results have identified trait-specific heat stress thresholds for production, fertility, and mitigation traits ranging from THI 55 to 67, where fat yield was the most sensitive to environmental pressures and first service to conception was the least sensitive. Genetic correlations estimated between performance under thermoneutral conditions and heat tolerance for production traits were found to be moderately unfavorable (-0.27 to -0.31), indicating a trade-off between productivity and resilience. Weak and favorable genetic correlations were estimated between methane emissions and heat tolerance of production traits, with the strongest relationships observed between heat tolerance of fat yield and methane emissions (-0.05 to -0.16). These results highlight the need for balanced selection strategies to improve both productivity and heat tolerance, while suggesting that selection for reduced methane emissions is unlikely to adversely affect heat tolerance. These findings will inform climate-smart dairy selection strategies balancing profitability, resilience, and environmental impact.
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