Q and A on Fly Resistance

Question: “In regards to fly resistance… since flies are attracted to testosterone, how do you ensure that in selecting for fly resistance in your bulls you are not inadvertently selecting low testosterone bulls?”

Answer: Good question. Several things come to mind. 1) How much testosterone is enough? Nearly all men with extra high levels of testosterone are behind bars. 2) We are evaluating and scoring young bulls. As bulls age, testosterone levels increase. 3) We have been at this long enough to know that bulls with good fly resistance scores can breed a lot of cows for many years. I am led to believe we can have both – fly resistance and adequate levels of testosterone.

I sent this question to Dayton Steelman, a retired entomologist at the University of Arkansas. He responded by saying, “In our studies we used bulls that had consistent low horn fly numbers and they did an excellent job of servicing cows. We collected no data on testosterone as we were getting excellent conception during each breeding season.

“Our research showed that horn fly resistance is genetically transferred by the bull to the female offspring. The use of the fly resistant genetics works by saving the resistant heifers as herd replacements and at the same time culling the mature high-fly cows. Then mate the fly resistant replacement heifers to a different fly resistant bull.”

“Generally, in a herd of cows there will be 25% that is fly susceptible (high-fly). There will be 50% that in times of high fly populations will be high-fly cows. The remaining 25% will have consistent low-fly numbers. By using fly-resistant PCC bulls, you can make big improvements in a relatively short period of time.”

Question: “I really enjoyed this week’s update! I was wondering what you use to judge the hair coat and fly resistance in your cattle?

Answer: Healthy, well-adapted cattle will have a lively looking hair coat year-round. During the winter months, the hair should have a soft “teddy bear” look and feel to it. In the summer, the hair coat should be short, slick and shiny – shiny enough to almost see your reflection. The presence of dull, dead hair will lower the hair coat score.

Evaluating and scoring fly resistance is not as difficult as some think. We simply assess how many flies each animal has. There is often a big difference between animals within the same herd. While a few animals are black with flies, others will have very few flies. In the cool morning hours, flies will be on the animal’s back. As the day warms up, the flies will move to the shaded areas of the belly and legs.