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Animal Health Notebook

The horn fly is summer enemy No. 1

Alan Newport Horn flies on cows
Horn flies drink large amounts of blood, and the larger the population the worse it is. Production suffers.
Despite its well-deserved and ugly reputation, management practices can help reduce horn fly pressure.

Back in early to mid-summer 2019 I remember a couple of days when several little winged guys (actually girls) with razors cut on me like I was in a back-Chattanooga neighborhood after midnight back in the late 60’s. I bled for several minutes and I’ve heard that giving blood is a good deal for health, but I don’t believe everything I hear. The razor-blade mouthpieces belonged to deer flies and I’ll take my pen to them later.

For now I am going to opine on horn flies, since they are likely the most costly parasite to North American beef producers. They are reported to cost producers in our country as much as $800 million dollars annually. There is likely well over $60 million being spent on their control every year. A lot of programs produce some degree of success. But it is often short-lived.

Horn flies are a problem mostly because of lost production from blood loss and irritation to the cattle. One threshold commonly used as a point where treatment pays is 150 flies and it normally means both shoulders are black with flies.

The horn fly’s No. 1 problem for cattle has to do with their blood-sucking meals that are performed as often as every 70 minutes. One horn fly removes in excess of 1cc of blood daily and at night. A load of 500 flies account for almost 1 pint of blood every 24 hours. A load of 1,000 flies can take a quart of blood daily in seven days. Yearling steers and heifers do not gain weight when donating a pint a day. A quart a day can take out a 1,000-pound cow in two weeks or less.

Horn fly facts

Here is part of what we know about horn flies. About 80% of the flies live on 20% of the cattle. Bulls are big attractors of horn flies. They love rough-hided, poor or doing individuals. Hormones are important. Taller cattle tend to have more flies.

Female horn flies leave the individual cow, calf, yearling or bull to lay their eggs in fresh manure then return quickly to the same animal.

Their life cycle takes seven to 21 days and their reproductive development requires non-disturbed manure that has a crust shortly after eggs are laid. Disturbance of the manure pats greatly reduces horn fly reproduction. Ground birds love fly larvae. Feedyard cattle don’t have problems with horn flies since the manure if disked by their hooves. Dung beetles and high-density grazing create similar benefits.

Horn flies favor moisture and warm temperatures and long growing seasons. With 25 inches of annual moisture and warm days and nights and you’ll have horn flies from late March through Christmas. The Gulf coast can raise them year around. That is a long season.

Horn flies do not like to fly. They can go considerable distances but it is not of their choosing. Long moves of 300 yards or more normally reduce fly numbers for one to three weeks.

Chemical control

Systemic fly control measures have caused problems. Chemical resistance is real. Further, there are a bunch of people that want a steak or hamburger that does not include bug dope. Fish kills following pour-on use also has been common for a long time. Horn flies quickly develop resistance to lots of insecticide compounds especially the synthetic pyrethroids of the earlier generation.

I run cattle in the lower mid-south. We average 50 inches and more of annual rainfall and it is usually well spread. We average warm temperatures and a growing season that has lasted all but 60 days for past 15 years. We’ve spent less than 25 cents per thousand pounds of cattle on fly control annually the past 10 years.

Eight management tips

Here are eight things we’ve done in central Tennessee to help with the horn fly problem:

  1. Herd the cattle in high densities of 70,000 pounds or more per acre
  2. Move cattle daily or more often and zig-zag most temporary poly wire fences. This increases cattle densities and trampling.
  3. Add calcium to the soil which has helped increase plant diversity and organic matter and life. Diverse life is a big deal and calcium is the mineral driver of life.
  4. We observe the cattle every day. We don’t count flies but we do pay attention. If a back is one-half black your animals has 400 flies and is losing 1 pint of blood daily.
  5. We allow pastures to recover completely before grazing. When we graze we mean to do so severely.
  6. We don’t declare war on a few bushes, weeds or a little brush. We like and need bird nests. Remember birds are your pasture first responders and cleaners.
  7. We spot spray cattle that need it with a non-systemic fly product that is “knock-down” but not a residual. We do this before a distance move. We do not spray or apply systemic insecticides or fly tags until there are lots of flies (mid-June). Truth is it has been over 30 years since I have used fly tags. We spray after and not before water.
  8. We work to eliminate cattle that can’t work at our place. Many are fly magnets.

I think there may be horn flies and several of their cousins around forever. But they do not have to cost us a bunch of money, health or production. The natural model can use them mostly for our advantage. Think about it. They help us locate the freaks and dogs. These are the cattle beef producers do not need and cannot afford. A few of us do this for a living and lifestyle.

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