The Dreaded Horn Fly

 By Kit Pharo

 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:
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.  Within a breed, some individuals are much more resistant to horn flies than others.
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.
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.
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.
Bulls, because of their testosterone, will typically have two to four times more flies than cows.   Flies are attracted to testosterone.
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:  
• 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.
• Replace your bulls with bulls that have good ratings for fly resistance.
• 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.
In the last 12 years, Pharo Cattle Company has evaluated and scored over 10,000 bulls for horn fly resistance.   Our cowherds have gone two decades without any chemical treatments for parasites (internal and external).  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.