To people, time flies when you're having fun. To frogs, time's fun when you're having flies. To cattle producers, however, "fun" and "flies" are never used in the same sentence. These pests cost the livestock industry hundreds of millions of dollars every year.
Consider horn flies — each one will take 20 to 30 blood meals each day and may travel a couple of miles to do it. They have been implicated in the spread of blood-borne diseases. Adults live almost two months. The 300 to 500 eggs the female horn fly lays can mature to adults in two weeks. Face flies reproduce even quicker (8 to 10 days) and in equal numbers. Face flies aren't "out for blood," but instead feed on the moisture around their hosts' eyes, nostrils and mouths. Face flies are one of the main means of spreading pinkeye. Then there are stable flies, horse flies and heel flies (the larval stage is the cattle grub).
The biggest cost of fly infestations is not disease or blood loss; it is the constant irritation and aggravation they cause cattle. Cattle will expend tremendous energy stomping and swishing, they'll head for the shade to lie down, stand belly deep in the pond or bunch up in groups to try to get some relief from the constant onslaught of flies. Horn flies, for instance, stay on cattle 24 hours a day. It follows that performance is going to suffer, and it doesn't take large numbers of flies to get into your pocket book. Most research has shown that the economic threshold is 100 to 200 flies per side, or 200 to 400 per animal.
That's not many flies for a significant loss in production. Threshold levels can reduce summer stocker gains by as much as 50 to 70 pounds over the season. Lower milk production in the cow and growth in the calf can reduce weaning weights by 20 pounds or more in the fall. So, fly control is a critical aspect of late spring, summer and early fall management and offers a cost:benefit ratio equal to implanting or internal parasite control.
There are many choices of control methods and products: sprays, pour-ons, dusters, rubs, ear tags, mineral and feed additives, dips, traps and boluses. The right one or combination depends on your own situation. Regardless of which you use, though, the fly population must be susceptible to the product. Regular monitoring and adjustments are needed to ensure adequate control during the season. It is a fact that fly populations can build resistance to any of the chemicals in these products, both the pyrethroids and their synthetics and the organophosphates. A standard recommendation is to rotate the class of product used each year to minimize this problem. Here are a few considerations associated with some of the methods.
Quick knockdown with some residual for 2 to 6 weeks depending on rainfall; several applications may be necessary; works well in combination with other methods.
Good knockdown as initial treatment; some only get blood feeders (systemic) so face flies aren't affected; others are topical (contact); generally limited to a month or so of control, so must be repeated or used with another method.
Can be effective as a stand-alone control for up to 5 months; don't apply until flies are present in near threshold numbers in late spring or early summer; use recommended number, usually two per animal; remove after 5 months of use (earlier if effectiveness declines); consider knockdown with spray or pour-on when tags are applied.
Can be effective as stand-alone control, especially if forced-use is possible; should be re-charged regularly, after each rain event or every 2 to 4 weeks.
Can be effective if maintained regularly and forced-use is possible; usually must be protected from weather to prevent caking
Available in mineral, block or feed additive; individual intake can vary with any self-fed product; does not control migrating adults from neighboring ranches or herds, so probably should be used with another method.
Most of the fly-control products have no withdrawal time, but some do. Most will also recommend a minimum treatment interval. As always, read and follow label directions.
Fly control is critical to the health and performance of cattle. While some methods and products may seem expensive and/or labor intensive, it is a practice that will more than pay for itself during the season. If you have any questions, call one of the livestock specialists at (580)224-6500.