When I take on new clients, I always ask them their short- and long-term goals. One producer stated his long-term goal as, “I want you to eliminate fly problems in my herd.”
I appreciated his frustration with flies, but his request was impossible. I simply replied, “I will fail in your quest to eliminate fly problems.”
Biting flies are carriers of such diseases as anaplasmosis and bovine leukosis virus. Face flies can spread Moraxella bovis, which causes pinkeye, from animal to animal. The economic loss from each horn fly biting an animal 30 times/day can also be substantial.
But flies have adapted to the environment for many, many years; realistically, there is zero chance that we’ll completely win the battle. I did, however, outline a multi-pronged approach for this producer to lessen flies’ impact.
Feed a larvicide or an insect growth regulator like Altosid® (labeled for horn flies) or Rabon™ (labeled for horn, face, house- and stable flies) to cows, starting 30 days before flies typically emerge. Continue until 30 days after a killing frost.
ClariFly® is also an option, but is mainly used for confinement cattle. If an adjacent property also has cattle, the owners of those cattle also need to feed the product to their cattle or you might inherit some of the neighbor’s flies. Horn flies don’t travel long distances, but face flies may travel 1-2 miles.
Fly tags. Newer-generation fly tags that contain a higher concentration of insecticide are quite helpful in quite helpful in controlling fly populations. Use pyrethroid tags for two consecutive years, then switch to an organophosphate tag for one year to reduce pyrethroid resistance. Follow label directions on the number of tags/cow.
Many tags require two tags/adult animal, and one tag/calf for optimum control. The key to using tags is to wait until you have 200 flies/cow to place the tags. If you apply the tags too early, you’ll have decreased efficacy. And be sure to remove the tags in 3-5 months, in order to prevent the release of minute amounts of insecticide that can lead to resistance issues.
When you walk cattle through the chute to fly-tag them, it’s also an ideal time to give initial vaccinations for bovine respiratory disease (BRD) control in calves. Calves can also be castrated, hot-iron dehorned and implanted at this time.
Note that bulls and potential replacement heifers under 45 days of age should not be implanted; all other calves should be implanted. The profit/hour for implanting calves destined for the feedlot is about $1,800/hour — well worth it!
Pour-ons. Use a pour-on at the same time you fly-tag the cows. If it’s spring turnout time, you can use a product that also kills internal parasites, as these products also have efficacy against horn flies. Later in the year, use products only labeled for flies and/or lice. Using pour-on dewormers many times throughout the year could lead to internal parasite resistance issues.
Dust bags/cattle rubs. The advantage of a dust bag or rub is that, if placed at a site where all cattle must use it, it can provide very economical control of face and horn flies. Proper placement and keeping it charged with insecticide are the keys.
Sprays. Timely spraying of cattle throughout the year can be effective in reducing the fly population, but can be time-consuming if cattle are grazing an extensive area.
There are many products on the market for fly control. Sitting down with your Extension beef specialist and/or herd health veterinarian to develop a plan to control flies is the best recipe for success. Using just one strategy from the above list likely won’t give you the results you anticipate. A multifaceted approach is best for attaining your goal of “controlling” flies.
Remember, you can’t eliminate fly problems, but you can lessen their negative impact.
W. Mark Hilton, DVM, is a clinical professor of beef production medicine at Purdue University in West Lafayette, IN.
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