The Dreaded Horn Fly

Many of the problems we encounter in the cow-calf business have a genetic factor.   Genetic selection is the only way to provide a permanent solution to many of our problems.   Horn flies are no exception.   It doesn’t take a genius to see that some cows have a fraction of the horn flies other cows have.   For one reason or another, some animals have a genetic resistance to the dreaded horn fly.

Dayton Steelman, a retired entomologist at the University of Arkansas, believes the heritability for fly resistance is 58% – which is very high.   With this in mind, we believe fly resistance is a trait all seedstock producers should be monitoring and selecting for.   Steelman studied horn flies and their effect on beef cattle for over fifteen years.   His research led him to the following conclusions:

  1. Some breeds, such as Brahman, are more resistant to horn flies.   They have a higher number of hairs per unit of surface area than do British and Continental breeds.
  2. Within a breed, some individuals are much more resistant to horn flies than others.
  3. Smaller framed animals have significantly fewer flies than larger framed animals within the same breed.   Cattle of the same breed seem to be born with approximately the same numbers of hairs.   When you enlarge the frame size, you have fewer hairs per square inch.   The taller the animal, the greater the distance between hairs.
  4. Every hair follicle has two sebaceous glands that secrete a substance that reflects sunlight (heat) and provides a natural resistance to insects.   The more hairs, the more secretion.   Cattle that have a very slick and shiny summer hair coat seldom have much in the way of fly problems.
  5. Horn flies have an anti-coagulate factor in their saliva that prevents blood clotting while they are feeding.   Some beef animals have a higher level of a natural chemical called thrombin that works to counteract the fly’s anti-coagulate.
  6. Bulls, because of their testosterone, will typically have two to four times more flies than cows.   Flies are attracted to testosterone.

Bred-in parasite resistance is one of many areas in which Pharo Cattle Company has assumed the leadership position.   We have evaluated and scored hair coat for many years.   In the last 12 years, we have evaluated and scored over 9,000 bulls for horn fly resistance.   As Steelman suggested, there seems to be a relatively high correlation between hair coat score and fly resistance score.

Most of our PCC cowherds have gone two decades without any chemical treatments for parasites (internal and external).   We have cooperative cowherds in a variety of environments from Minnesota to hot, humid, fescue country in Missouri and Mississippi and all the way to the high-plains desert.   We also have cooperative herds from the southern plains of Texas all the way to the northern plains of Montana and North Dakota.   We are doing what members of the status quo herd say cannot be done.

NO ONE has as much bred-in parasite resistance as Pharo Cattle Company – because no one else has ever tried to select for genetic parasite resistance.

Horn flies cost beef producers over $800 million every year in production losses.   Research has shown horn flies can reduce daily gains by as much as ½ pound per day.   That could amount to 100 pounds per calf at weaning.   Do the math!   At $1.80 per pound, that is a loss of $180 per calf.   What’s a bull worth that can genetically improve the fly resistance of your herd?

Horn flies are becoming more and more difficult to control with insecticides because the flies are able to develop a resistance in just a few years.   The end result of using chemical insecticides is the creation of genetically superior flies – and genetically inferior cows.   Chemical insecticides are also responsible for killing a multitude of good bugs and organisms.   Dung beetles, for example, are nearly extinct on most farms and ranches.

How are you going to solve your fly problem?   Will you continue to spend money on toxic chemical solutions that only provide temporary relief – or will you permanently fix the problem with genetics?   If you are serious about eliminating the need for fly control, here are three simple steps:

  1. Identify the 25% of your cowherd that has the least fly resistance.   Cull and replace those cows as soon as possible.   They are your least profitable cows.
  2. Replace your bulls with bulls that have good ratings for fly resistance.
  3. Repeat number 1 above for three or four years.

With the heritability of fly resistance at 58%, you will make big improvements in a short period of time.


NOTE: We have been sharing our hair coat and fly resistance data with the U.S. Meat Animal Research Center in Nebraska in hopes that they will be able to identify some DNA markers for these traits.

One response to “The Dreaded Horn Fly

  1. Very interested in one of your bulls, Red Angus..  I am in NW IL. Where is the closest of your affiliated farms to me?  Thanks

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