Flies on Pastured Cattle

Face flies on a cow

With summer in full gear it is a good time to evaluate how your fly control program is working. When horn fly numbers are greater than 200 flies per animal we see significant production losses associated with blood loss and decreased feed consumption. Numbers of face flies and stable flies are harder to assess because they only spend a small amount of time feeding on cattle but are still significant pests.

Any pour-ons that were used at grass turn out are no longer effective and re-application could be beneficial. Fly tags should still be providing some protection but are probably about half way through their protection window. Feed through larvicide products if used should be continued but it is probably too late to start as there will have already a large number of larvae developing.

If cattle are being bothered by flies now an insecticide pour on or back-rubber would be most practical at this time. Back-rubbers are fairly easy to set up but will need to be recharged regularly to get the cows through the rest of the summer. Pour-ons will only be effective for a few weeks but can be useful to knock population of flies down rapidly. When pouring cattle this time of year it is a good opportunity to assess cows overall, is the bull still healthy and active, any disease issues such as foot rot or pinkeye in calves, are cows getting bred or are there still quite a few still cycling? This is also a good time to start calves preconditioning vaccines as long as they are at least 4 months of age.

Besides causing production losses flies can also transmit diseases which increases the importance of good fly control programs. Additionally, when cattle bunch up because of fly irritation they can damage pastures or facilities due to the heavy concentration of cattle. Injuries to feet or eyes can also occur when cattle bunch up. The Iowa Beef Center has a fact sheet available to help you manage flies on your farm, IBCR 204.