Don’t Let Flies Make Your Cattle Poor Performers

   If one pesky house fly can ruin a picnic or family evening, think how cattle must feel. “Imagine how cattle feel when several hundred, blood-sucking horn flies converge on them as they graze or rest in the shade,” said Eldon Cole, a livestock specialist with University of Missouri Extension.
   Horn flies contribute to poor performance that on yearling cattle may result in around a 0.2 pound per day reduction in gain.
   “Beef cows will also be affected by heavy fly populations although I don’t recall seeing estimates how much their nursing calves suffer due to reduced milk production. Nor do I remember any research blaming lowered conception rates on horn fly populations,” said Cole.
   There are numerous ways to reduce the aggravation of horn flies on beef cattle. For the most part, the controls are reasonably priced when compared to the value of lost cattle gains.
   “Methods of fly control seem to change over time. Spraying was the norm for years. It’s still effective, but does require repeated treatments and labor that many farms have trouble finding,” said Cole.
   After sprays, the self-treating systems, dust bags and backrubbers, were fashionable and still may be the most economical method to control horn flies. The main complaint is that cattle won’t always go under them regularly.
   “Most farmers can figure out a way to trick their cattle into moving under the devices every two or three days,” said Cole. “Locating the rub near mineral or salt, water, shade and pasture gateways usually work.”
   In addition, producers must be regular in applying the pesticide to the bag or rub.
   Insecticide treated ear tags came along in the late 1970’s and were very effective until the resistant fly buildup according to Cole.
   “They are still useful when the different insecticides are rotated and application instructions followed closely. Be sure and protect yourself when handling the tags by wearing gloves and working in a well-ventilated area,” said Cole.
   There is growing interest in using oral larvacides or feed through materials that prevent the development of horn flies in fresh manure. Including those products in minerals is the most used method to get the growth regulator in the animal.
   “The limitations are that all cattle may not consume an adequate amount of the mineral to control the fly population, cost may seem high and if neighboring cattle are not eating the product there could still be a big fly population on the cattle as they migrate across the fence,” said Cole. 
   No horn fly control method will be 100 percent effective, but most do help reduce the population to 200 flies per adult animal. Cole says that for some reason, horn flies seem to favor certain animals within the herd, more often adults, and they really like bulls.
   “You also find that certain colors tend to attract heavier numbers. Research is also being conducted to look at cattle’s genetic makeup that causes some to attract more flies,” said Cole.
   The secret to having good control of the troublesome horn fly is to get started early and keeping up the protocol. Cole says to supplement other treatments later in the season if the method you are using isn't working as well.
   “For example, some fly tags may lose effectiveness in late summer so consider a spray, pour-on or even set up a backrubber during that time,” said Cole.
   Small herd owners with gentle cattle often have great success hand-treating with dust or misters when the cattle gather for a few cubes or fresh salt.
   Persons who choose to not use insecticides may be interested in building a walk-through fly control device. It has been able to reduce fly numbers by 50 to 60 percent.
   “Feeder and breeding cattle prices promise to be high enough this year that an extra effort should be made to reasonably control fly numbers and avoid reduced animal performance,” said Cole. Δ

A portable backrubber that’s connected to a mineral feeder that’s designed to be pulled by a four-wheeler from pasture to pasture. Photo by Eldon Cole

One view of a walk-through horn fly trap referred to at the end of the article. Photo by Eldon Cole

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