Flies cause significant welfare harm to livestock through biting, disease transmission, and myiasis, and effective control reduces suffering across all production systems.
Fly pressure on livestock is a welfare problem that is easy to underestimate because the harm is diffuse and chronic rather than acute and visible. Cattle under severe horn fly pressure spend less time grazing, more time bunching and seeking relief, and show reduced milk production and weight gain. The chronic stress of persistent biting activates immune and stress responses that have downstream health consequences. Effective fly control through manure management, biological control agents, and targeted insecticide application reduces this welfare burden while also reducing the risk of fly-transmitted diseases. Control methods that allow animals relief from fly pressure also demonstrate their welfare significance through the immediate behavioural improvement in treated animals.