"Flies are the biggest cost to the industry - even larger than respiratory disease," reports Marc Campbell, a Technical Services Veterinarian with the Cattle Business Unit of Huvepharma, Inc.
Campbell explains that the cost to the industry is mostly due to loss of gains - as much as 12 to 15 pounds/animal - on pastured cattle, where flies can be challenging to control because fly eggs are continually being laid and hatched in the cattle manure.
Campbell advises, "It is impossible to completely eliminate horn flies and face flies, but you want to reduce their numbers so you can minimize their impact to cattle performance." The economic threshold is to strive for fewer than 200 flies per animal.
Campbell acknowledges that fly tags and chemical control - via pour-ons, cattle rubs, and sprays - are common fly control methods with merit. But they also have some drawbacks. Fly tags can be expensive and labor intensive to run cattle through the chute and administer - and later remove. And, because there are only three classes of approved active ingredients among chemical fly control products, resistance to these products is a growing concern.
Additionally, with regard to face flies, Campbell points out, "Dewormers don't affect the face, so they are not effectively controlling face flies. And fly tags don't necessarily kill face flies, they just ward them off."
Thus, Campbell encourages producers to consider utilizing feed-through fly control products, which are additives that contain an insect growth regulator (IGR). These products can effectively be fed to cattle on grass with a free-choice mineral or feed supplement. "Feed-throughs control horn flies and face flies in the cattle dung where flies are laying their eggs. These products kill the fly larvae or prevent the larvae from maturing depending on the mode of action," he explains.
Because feed-through fly control products use a different mode of action (diflubenzuron) than fly tag and other chemical fly control products, Campbell also notes, "Feed-throughs have no known resistance."
Campbell underscores that using a combination of fly control methods can help provide the most effective results. As well, for fly control to be effective it needs to be a season-long effort.
In short, fly control is about more than just eliminating a nuisance. With flies being one of the biggest costs to the industry, control is key to avoiding loss in gains, preventing pink eye and ultimately increasing profits.