Calves and Flies Don’t Have to Coexist
Summertime is fly time, and calves are a popular target for fly breeding grounds. Their bedding and feed provide the perfect haven for flies to set up shop and multiply in mass.
Left unchecked, fly populations can double every 40 to 60 days in the spring and fall, and as rapidly as every 2 weeks in the hottest summer months, according to University of Minnesota entomologist Roger Moon. That’s bad news for calves and young heifers, whose growth can be delayed by the stress that flies create. Flies also can serve as vectors to spread diseases like salmonella, E. coli, and pinkeye between calves.
Moon told the audience of a recent webinar sponsored by the I-29 Dairy Coalition that the two most common types of flies on dairies are stable flies and house flies. Stable flies bite, draw blood, and are a painful stressor to animals, including calves and their caretakers. House flies are more of a nuisance, but are more likely to spread pathogenic bacteria.
According to Moon, fly maggots need organic matter, moisture, and warmth to survive. “Fibrous plant material, enriched with manure and urine, is the perfect breeding ground for flies,” he shared. “Fresh manure is too young and too wet for fly breeding.” He said soiled calf hutch bedding is a common fly-breeding medium, as is spilled or wet, leftover feed.
Chandler, Minn. dairy producer Merri Post shared the measures she takes to limit fly populations on her dairy, which include:
1. Fresh bedding and manure management – The Posts strive to clean out their tunnel-ventilated calf barn every 2-3 weeks in the summer, and haul away any piled manure around the farm by early May.
2. Scavengers – Free-range chickens comb the farm’s environment and routinely thin the population of maggots in old manure piles.
3. Fly traps – Post places traps away from livestock barns to draw fly populations to more remote areas and suppress them. These bait traps catch house flies and metallic blow flies, but not stable flies.
4. Feed-through larvicides – Starting in April, Post switches her calves to a milk replacer supplemented with a feed-through larvicide that contains an insect growth regulator (IGR), diflubenzuron, and incorporates the same additive into all feed rations for older animals on the dairy as well. When it passes through the animals, it is dispersed via manure into their bedding, where it helps to break the fly life cycle and reduce populations. She continues to feed it until the weather freezes in the fall.
5. Insecticide sprays – Fly pressure often requires that Post sprays for flies in her calf barn feeder room, and sometimes the milk house. Since they switched to tunnel ventilation in their barns, these enclosed rooms are the only areas on the farm that need spray for back-up fly control.
6. Vegetation management – Post mows faithfully throughout the summer around all outbuildings and the manure lagoon. While it keeps their place looking tidy, it also removes a haven for flies to breed and develop eggs.
This year Post plans to also experiment with releasing predatory wasps to manage fly populations, which Moon predicted would work well because of the overall cleanliness of the Posts’ farm site. “On the other hand, if you have tons of breeding matter, like a lot of manure piled around, you can’t release enough wasps to stay ahead of the flies,” he advised.
Post said she believes the combination of the multiple steps they take to control flies are necessary to be successful. “In the past, we’ve had a couple of extra-busy years when we didn’t stay on top of these details as well, and by the end of the summer, we were paying for it with stressed animals and a lot more pinkeye in older heifers,” she shared. “It’s truly a situation that is much easier to prevent than to cure.”
