Flies, primarily horn flies, cause a loss in animal performance. We usually say the economic threshold for flies is around 200 per head. I’ve seen data supporting the fact that steer gains can be improved around 0.2 lb. per day when effective fly controls are used versus none. A recent Arkansas Beef Cattle Research Update reported on cow milk loss in a cooperative study in Arkansas and Oklahoma.
The trial compared several different breeds. The study had fly counts ranging from 94 per head early in the season to a peak of 503 flies in August. They did see milk yields drop, especially in some breeds, as fly counts increased. This would seem to affect calf weight gains. They suggest that selecting cattle for parasite resistance may be a consideration in the future.
Selecting for resistance is a very long-term project, but keep it in mind as you observe your cattle this summer. You may even make some notes about which animals in your herd appear to be fly magnets. Short-term control of horn flies has several options. I’m still pretty biased towards the use of back rubbers or dust bags for economical fly control The rub needs to be located so the cattle pass under it daily.
Fly tags still offer help for fly control if they’re applied around this time of the season. Often they are applied in early April and their effectiveness diminishes by the time big fly number occur. An animal’s ears also only can accommodate so many tags over time without appearing to be mutilated.
Last year Kansas State animal scientists conducted a 77-day grazing trial comparing no fly tags, 1 fly tag per animal or 2 tags per steer. The study was done in the Flint Hills and due to the dry weather the trial stopped early. Numerically there were differences in daily gain (1.45, 1.53 and 1.58 lbs.) going from 0 tags, 1 tag and 2 tags. However, the differences were not considered statistically significant.
Feed thru or oral fly controls seem to be gaining in popularity. They are effective if started early in the season and your cattle consume the adequate amount of mineral. We do caution that cattle across the fence on the neighbor’s place that doesn’t use the oral product can have flies that find your cattle. Get your pencil out and look closely at the comparative cost, convenience, etc. of the various methods of control.