Pest flies on dairy farms affect behaviour and welfare of dairy cows during summer season

Monitoring of changes in the behaviour of dairy cows related to the occurrence of insects in the stable and in the milking parlour was carried out on a selected dairy farm during the summer season. The effect of the number of insects on the occurrence of huddling of dairy cows in the stable was proved. Huddling occurred significantly (P = 0.003) more often when the number of insects captured by fly glue traps exceeded 500 individuals. The occurrence of pest flies affected also the behaviour of dairy cows during milking. With the increasing number of insects captured by glue traps in the milking parlour, the cows more frequently kicked off the milking units (r = 0.944, P < 0.001) and defecated (r = 0.940, P < 0.001) during milking. In addition, the increasing number of captured insects correlated with a significantly lower milk yield in cows (r =-0.709, P < 0.001). The number of insects in the stable also correlated with the incidence of mastitis in dairy cows on the monitored farm (r = 0.681, P < 0.001) during the summer season. The study shows that pest flies affect the behaviour of cows which is further reflected in their health, milk production and thus the overall farm performance.