Abstract
This study aims to identify the effects of temperature on dairy production and the heat tolerance of different dairy breeds under heat stress. Using farm and animal-level data from 1435 dairy farms throughout Sweden for 4 years (from 2016 to 2019), we find that a 7-day average of daily maximum temperatures above ~ 20 ºC is associated with sharp declines in milk production. We then estimate the farm-level loss in contribution margin for a typical Swedish dairy farm for the year 2018, which consisted of long-lasting heatwaves and extended summer temperatures. We also estimate that, on average, there are no differences in the impact of heatwaves on milk losses for different dairy breeds but that there exists a trade-off between genetic milk production potential and heat tolerance of a dairy cow. The magnitude of this productivity-tolerance trade-off may differ across breeds, suggesting that the high-production potential animals of certain breeds may be less sensitive to heat stress. These findings have important implications in terms of adapting to heat stress, investing in mitigation measures, and development of future breeds that can ameliorate the current trade-off between production capacity of a cow and its heat tolerance.