When does heat stress start in Swedish dairy cows?

Climate change is increasing the frequency and intensity of hot weather events, exposing dairy cattle in temperate regions such as Sweden to periods of heat stress. This can negatively affect animal welfare and milk production.

We have investigated how Swedish dairy cows respond to warm summer temperatures. Using data from the SLU dairy data collection infrastructure Gigacow, the study analyzed more than 3,000 lactations from Holstein, Swedish Red, and Jersey cows across 10 dairy farms in southern Sweden.

The results showed that milk production began to decline when the daily maximum temperatures reached around 21 °C over several days, regardless of breed. The study also found that the impact of heat varied depending on the cow’s breed, stage of lactation, and number of calvings. High-producing cows in mid-lactation appeared to be especially sensitive to warm conditions.

These findings suggest that even in Sweden, summer heat can reduce milk production and affect dairy cattle. The study highlights the importance of developing management strategies to help cows cope with increasing temperatures in the future and lays groundwork for further studies of the genetic basis of resilience against heat stress.

Publication

The project has been funded by FORMAS and The Beijer Foundation.