AgWatch

Fly Control On Cattle Is Critical

NASHVILLE, TENN.
   The economic loss due to fly infestation in cattle herds has been well documented. Depending on the type of fly and class of cattle, reported economic losses vary but the consensus is that the problem can result in millions of dollars lost to decreased weight gain and health treatments. There are three major ways that flies reduce performance: through reduced grazing (because cattle are searching for a way to ease the irritation), as a result of sucking blood from the cattle, and through spreading disease.
   Horn and face flies are the two major flies that cause problems for Tennessee beef cattle producers. Horn flies are small, about half the size of a housefly, and usually concentrate on the withers, back, sides and the underline (where most of the biting occurs). Reduced weight gain from horn flies is caused by irritation (and the resulting decreased grazing time) and blood loss.
   Normal populations of horn flies usually average several hundred, but as few as 50 flies per animal can be enough to negatively impact performance. Thousands can occur and that many can consume enough of the cattle’s blood to make it become anemic. While most of the discussion around horn flies focuses on irritation and blood consumption, they can also transmit causes of blood-borne diseases like anaplasmosis.
   Face flies more closely resemble houseflies. They concentrate around the eyes, nose and mouth where they feed on the mucosa found in those areas. Since face flies congregate around the eyes and can carry the causative agent of pinkeye, controlling them can help slow or limit the spread of pinkeye. The spread of pinkeye by face flies makes their economic impact two-fold. The disease reduces average daily gain in calves and performance of cows but also reduces the value per pound of calves at marketing due to eye problems.
   Several methods, and many products within those methods, are available to control flies. These methods include slow-release ear tags, sprays, rubs, dusts, feed through and boluses. The most common methods in Tennessee seem to be ear tags, sprays and rubs. The chemicals that these methods deliver include pyrethroids, organophosphates (OPs), organochlorines and endectocides.
   Consider these factors when choosing a fly control program:
   • Young cattle require more attention than cows and bulls because prevention has a direct economic affect through average daily gain. They also are more susceptible to pinkeye.
   • Fly tags are convenient but should be used in combination with other methods to achieve full-season protection. – Use sprays or rubs early in the season and ear tags as late as economically reasonable.
   • Self-applicators (face rubs and mops) can be effective ways to deliver concentrated doses of insecticide.
    – These methods should be located in an area where the cattle come in frequent contact with them.
   • Horn flies quickly develop resistance to first generation pyrethroids.
   – New formulations are slower to build resistance.
   – Alternating with OPs can mitigate resistance. Δ
   DR. JUSTIN RHINEHART: Assistant Professor and Extension Beef Cattle Specialist, University of Tennessee

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