Cattle Fly Burden and Welfare in Summer

Fly burden in cattle during summer months causes significant welfare harm through pain, blood loss, reduced grazing, and behavioral disruption, yet effective management options exist.

Key Facts

Face flies and horn flies each inflict hundreds of bites per day on affected cattle
Fly-stressed cattle spend significantly less time grazing and more time bunching and head-throwing
Cattle with high fly burdens show elevated cortisol levels and reduced weight gain
Horn fly infestations can cause blood loss of up to 1 mL per fly per day — significant at high burdens
Effective fly management includes ear tags, pour-ons, traps, and biological control using parasitic wasps
Resistance to pyrethroid insecticides is increasingly common in horn fly populations

Welfare Considerations

Fly burden is a welfare problem that intensifies throughout summer and affects virtually all outdoor cattle operations to some degree. The visible behavioral responses — bunching, head-shaking, tail-lashing, running — represent attempts to escape from an incessant source of pain and irritation. Cattle cannot graze normally under high fly pressure, leading to welfare harms that compound reduced productivity. Integrated pest management combining targeted insecticide use, biological controls, and environmental management (manure management to reduce breeding sites) minimizes chemical resistance while maintaining welfare. Welfare-conscious producers monitor fly burdens regularly using standardized counts and intervene before burden reaches levels causing behavioral disruption.

What You Can Do

Monitor fly burdens on cattle using standardized counts and intervene early in the season
Implement integrated pest management combining multiple control strategies to reduce resistance development
Work with your veterinarian to select appropriate insecticide products and delivery systems
Use manure management and drainage improvements to reduce fly breeding habitat near housing
Provide shade and cool water during peak fly season to help cattle cope with fly stress