Heat stress reduces milk production and modulates milking behaviour in Girolando cow managed in a pasture-based automated milking system under tropical conditions

It is well documented that heat stress impacts dairy cattle; however, the effects of heat stress on Girolando cows managed in automated milking systems (AMS) under tropical pasture conditions have been less explored. We aimed to evaluate the effects of environmental variables on milk yield and milking behaviour of Girolando cows managed in a pasture-based automated milking system. To achieve the aims, two databases were used. The first database was composed by 44,112 records of milking events obtained between January and August 2025 from an automated milking farm, and the second database was composed by 5,377 hourly environmental variable records from NASA-POWER. Daily milk yield per cow was negatively associated with both the number of hours with air temperature of ≥ 30 °C (p = 0.001) and relative humidity (p< 0.001). Additionally, the number of milking events decreased as relative humidity (p< 0.001) and the number of hours with air temperature ≥ 30 °C (p< 0.001) increased. Furthermore, mean air temperature (p< 0.001) and relative humidity (p< 0.001) increased the interval between milkings, milking box time and milking time. The percentages of incomplete milkings (p< 0.001) tended to increase with rising air temperature, whilst the percentage of blood (p< 0.001) increased in association with air temperature, relative humidity and the number of hours with air temperature ≥ 30 °C. Our results demonstrated that environmental conditions impacted milk production and milking behaviour in Girolando cows in a pasture-based automated milking system.