Head fly raises summer mastitis risk

SUMMER MASTITIS  could be a big threat in dry cows and heifers this year as an explosion in head fly numbers is predicted following mild winters in many regions.

Higher fly survival rates will produce higher populations earlier in the season, warns the VLA’s head of entomology Peter Bates. “June and July is the start of the danger period when the adults emerge and lay eggs. They tend to be gone by September. So if head fly is a problem, start to treat now.”

Head flies lay eggs on dead and decaying vegetable matter – such as pine needles – and one breeding cycle is enough to produce large swarms for the whole summer, says Dr Bates. Although they feed on body sweat and secretions from eyes and udder, not blood, they transmit summer mastitis.

Don’t wait until flies appear to apply insecticide, advises Schering-Plough vet Paul Williams. “Treat cows now to keep the fly population low and prevent it building up. Reducing adult numbers before they lay eggs will also lower fly numbers next year.

“Head flies spend less time on an animal compared with a resident fly. Insecticides can have 8-10 weeks duration of activity, but trials show monthly applications of a deltamethrin-based insecticide had the most significant reduction in fly numbers. Flies need to take up a lethal dose.”

Somerset-based vet Peter Edmondson has seen cases of summer mastitis drop significantly since producers grazed dry cows and heifers away from woods and stagnant watercourses. “They are also controlling flies and separating any infected stock. Housing also helps as the head fly doesn’t go into buildings.”