Ask The Vet

Fly Management Challenges

Image by Victoria G. Myers

Q: We use a feed-through fly control in our mineral, but I’m afraid we didn’t start it early enough. The flies seem to have gotten ahead of us. What is the best fly control to pair with a feed-through?

A: Every year is different, and weather patterns have a huge impact on fly control. I think we must have a realistic goal of control and not think of this as total elimination of flies.

Horn fly control is by far the most important because they can carry disease, and can drain enough blood through biting to cause a severe economic drain on a cattle production operation. Face flies do not bite but feed on secretions around the eyes. They are a significant factor in pinkeye transmission.

Even if you had started the feed-through earlier, in most cases you would have needed other control methods over the course of a season. Effective fly control utilizes an integrated pest management (IPM) program. Selection of the right class and application method are where professional advice is most valuable. Talk to your herd veterinarian, local extension agent or other experts to help develop a customized program specific to your operation.

I believe some type of feed-through (larvacide or insect growth regulator) should be part of every IPM program. There is little documented resistance to these products. Feed-throughs should ideally be started before flies emerge in the spring, and their use should continue until about a month after the first killing frost.

Insecticides can be incorporated into your IPM by various methods of delivery. Ear tags have been a mainstay of fly control for many years, but since they lose effectiveness over time it’s best not to apply them in the early spring. Rather, wait until horn fly numbers reach economic thresholds of about 50 flies per cow. Be sure to remove tags in the fall. Always follow label directions as to the number of tags to apply and whether calves also need to be tagged.

Pour-ons can also be effective in reducing fly numbers, but they do require working cattle through a chute. Pour-on dewormers provide some fly control and can be part of an IPM program, but they should never be used strictly for fly control. Many experts feel repeated, indiscriminate use of the generic ivermectin pour-on products, for example, have selected for resistance in intestinal parasites to this important class of dewormers.

Other options to manage flies include sprays, which may be less time consuming and less stressful than a pour-on because cattle only need to be penned to be treated. Some producers like the VetGun; I call it an insecticide paintball gun that delivers a dose of insecticide. Backrubs and dust bags are old standbys that can be quite effective, but cattle must be forced to walk under them to get to water or minerals, and they must be kept charged.

Lastly, parasitic wasps and fly traps are non-insecticidal concepts that may help in some operations. And don’t forget, pasture rotation and manure management around heavy use areas can go a long way in reducing fly populations by limiting breeding areas for the pests.

Readers Talk Back:

Wow, we asked for comments from readers on what they look for to identify a sick animal, and we got some great responses. Here are just a few:

> Watch for droopy ears or eyes.

> Note any cattle holding their heads down.

> A dry nose can indicate a problem.

> Discharge from cattles’ eyes or noses is never good.

> Pay particular attention at feeding time to cows or calves slow to come up to eat, or those that stand away from the herd.

> Healthy cattle should stretch when they get up. If they don’t, they may be in pain or sick.

> Have a good identification system to record sick or suspected sick animals, and to keep a close watch on them more than once a day. Communicate this to other family members or workers.

> Cows or calves last in line when the herd is on the move, as well as those on the periphery when loafing, may be sick.

> It’s a concern when an animal has a lack of “eye interest” when someone moves toward them. In healthy animals, eye contact should bring on a fight or fright response.

> Respiratory stress has a number of indicators, such as standing with the head down for extended periods, unusual extension of the neck to straighten airways, and/or exaggerated nostril flaring.

> Constant consumption of water can be an indicator an animal is overheating, but as its condition deteriorates it will often quit drinking like it should. That becomes another indicator of sickness.

> If there are any doubts, get the cow or calf up and check their temperature.

Please contact your veterinarian for questions pertaining to the health of your herd. Every operation is unique, and the information in this column does not pertain to all situations. This is not intended as medical advice, but is purely for informational purposes.

Write Dr. Ken McMillan at Ask The Vet, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email


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