In heavy infestations, losses in the lactating herd can result in decreased milk production and increased mastitis. Flies can also transmit anaplasmosis. In heifers, fly infestations can result in less than expected weight gain as well as increased incidence of pink eye or conjunctivitis. Flies can also cause mastitis in heifers. There are two types of flies that create a nuisance for cattle.
Heavy infestations can result in significant blood loss.
Adults lay their eggs in fresh manure where the larvae can feed until they reach adulthood and subsequently parasitize the animal host. They cannot complete their life cycle without fresh, undisturbed manure. For this reason, face flies and horn flies are not found frequently on animals that are confined to free stalls or tie stalls because the fresh manure is constantly disturbed or removed. Rather, they are found on heifers, dry cows, or lactating cows in operations where pasture forage is utilized as a major portion of their nutrient intake and the manure patty remains intact. The second type and most obvious fly found around the dairy is the house fly.