Effects Of Biting Flies On Cows

By Dr Jolly Kabirizi

Biting flies, including stable flies and horn flies on a dairy farm are more than an irritation for animals, workers, and neighbours. They affect the health and comfort of animals and reduce feed intake impacting weight gains, milk production and milk fat content.

• Cows become restless and spend less time lying down when under heavy fly pressure.
• High levels of biting activity of stable flies and horn flies can reduce cattle weaning weight, feed conversion efficiency, weight gain, milk production, and overall farm profitability. 
• Biting flies elevate physiological stress of animals as indicated by increased cortisol levels. Stress responses are associated with animal age with younger cattle reacting more strongly to biting flies than older animals, potentially resulting in greater economic damage as young cattle are in a period of rapid growth. 
• Some filth flies have painful bites resulting in animal disturbance, alteration of normal animal behaviours or self-inflicted wounds as animals attempt to avoid or evade pests. Irritation caused by biting flies can cause animals to express fly-repelling behaviours such as head shaking, ear flicking, leg stamping, skin twitching, tail swishing, or scratching. Incidence of these fly-repelling behaviours is generally related to the number of flies on the animal.