With the summer halfway through and extreme heat events continuing across Europe, heat stress and welfare are important to consider. Heat stress in cows occurs when the combined internal and external temperature of an animal is above what the animal can dissipate, causing behavioural and physiological adaptations and leading to an increased core body temperature. As dairy cattle have a metabolic process that expels high heat, they are more susceptible to heat stress. Heat stress causes welfare, health, and productivity (i.e., fertility and milk production) concerns. Earlier this year, an article about behavioural changes in cattle experiencing moderate heat loads was published. The article, from Switzerland, focused on dairy cows in pasture grazing systems between June and September 2021 and used the temperature-humidity index (THI) to report high and low heat events. Holinger et al. reported various behavioural differences between cattle during high and low THI events. The most apparent differences were a decrease in lying time, an increase in activity and an increase in crowding or grouping of cows on days with high THI compared to low THI. The authors proposed these behaviours may indicate when cows are experiencing heat stress on pasture. Other influences, such as insect activity, need to be further investigated. To reduce incidences of heat stress, water and shade should always be available to cattle on pasture. When possible, shifting the time cattle are on pasture to early morning or evening to avoid the hottest time of the day is also beneficial. 

Holinger, M., Bühl, V., Helbing, M., Pieper, L., Kürmann, S., Pontiggia, A., Dohme-Meier, F., Keil, N., & Ammer, S. (2024). Behavioural changes to moderate heat load in grazing dairy cows under on-farm conditions, Livestock Science, 279, 105376. https://doi.org/10.1016/j.livsci.2023.105376.