When does heat stress become critical for dairy cows? An index makes this measurable. Agroscope has carried out recent calculations for four of its own sites.
For the evaluation, Agroscope used data from MeteoSwiss to calculate the heat stress index for the years 1991 to 2023 (up to 15.7.23) for four of its sites. The chosen sites are in cantons where above-average numbers of dairy cows are kept per farm compared to Switzerland as a whole. The heat stress index – or temperature-humidity index (THI), to give it its technical name – allows the stress on a dairy cow to be estimated. It can be derived from the air temperature and the relative humidity.
Temperature Humidity Index: Changins, Avenches, Posieux, Tänikon
The dark grey strip in each graph indicates the normal range, where half of the observations for the years under investigation are located. Light grey indicates the range of extreme values. The black line maps the changes from 1.1.2023 to 15.7.2023. The evaluation shows that the limit value (salmon-pink line) was almost reached at all evaluated sites as early as mid-June and was exceeded in the week starting 10 July. The thunderstorms from 11 to 13 July brought some relief, but the situation remains tense.
Agroscope additionally investigated whether meteorological data are suitable for short-term prediction of milk yield. Researchers also studied the effects of heat stress on dairy cows. An FiBL video shows how the problem can be alleviated.
Even in temperate climate zones, an increase in the ambient temperature and solar radiation can cause heat stress in grazing dairy cows. Agroscope studied the physiological changes in cows caused by increasing heat load.