Spatially explicit estimation of climate change related heat stress on the milk production of dairy cows in the United Kingdom

Abstract

The impact of climate change on dairy cows' milk production in the UK has been investigatedusing a gridded modelling approach. 12 milk loss calculation methods based on the TemperatureHumidity Index (THI), which accounts for the impact of heat stress, and eleven climate projections(UKCP09) with 25 km spatial resolution and covering the 1950-2100 period were used in thestudy. Half of the investigated methods used daily meteorological data. The other methods usedfiner temporal resolution input data. The number of days when dairy cows are projected to beaffected by heat stress will increase sharply as we approach the end of the century: e.g. InSouthern-England, the number of days of heat stress increases from an annual average of 10(baseline: 1990s) to over 40 per year. The associated milk loss will rise from a 30 kg/cow/yr up to200 kg/cow/yr. In extreme years in the South the annual milk loss may exceed 1000 kg/cow. Bythe end of the century, dairy cattle in large portions of Scotland and Northern Ireland willexperience the same level of heat stress as cattle in Southern-England today. The number of dayswhen daily step methods result in no milk loss while sub-daily time step methods result in nonzeromilk loss increases throughout the century. Consequently, simple methods that use onlydaily average temperature and relative humidity values may underestimate the impact of heatstress in the future.