Dealing with summer external parasites


MOUNT VERNON, Mo. — During a year’s time, beef cattle are exposed to a variety of insect pests that may impact their performance, according to Eldon Cole, a livestock specialist with University of Missouri Extension.

Examples include the common horn fly (which shows up in huge numbers in mid- to late-summer if not treated against) and other fly insects like stable flies, horseflies and face flies.

“Each of these flies requires a different situation in which they thrive and do economic damage to cattle. Controls vary in effectiveness and cost as well as application methods,” said Cole.

Ear tags

The blood sucking horn fly is not viewed as an economic problem until numbers approach 200 per animal.

At that time there are many routes to follow. Insecticidal ear tags have a good track record and can still be used, but do not apply too early in the season.

Companies that make this product claim three to five months of control. Tags applied before May will be giving less than desired control during the peak fly season.

“The other concern with the fly tag is their resistant fly control. Some flies have developed a tolerance to the pesticide used in them,” said Cole.

Several different products are now incorporated into the tags and rotating tag types from year to year is helpful.

Cost of the fly tags vary from 75 cents to $2 per tag. Some brands recommend one tag per ear, thus doubling your cost.

“The older tags are pyrethroid or organophosphate and there is a new compound out this year that shows promise,” said Cole.

The fly tags must be removed at the end of fly season as the low level of tag activity can contribute to the development of resistant flies.

“These tags also are not as popular in herds where numbered ear tags are used in both ears for identification purposes,” said Cole.

Feed products

Feed-through products or oral larvacides also are popular because they do not require handling of the cattle through a chute.

According to Cole, feed products do come at a cost and may not provide adequate control if herds across the fence are not being managed to control their horn fly problem.

Periodic spraying is effective, but may not be practical.

Self treating

Year in and year out, self-treating devices such as back rubbers or dust bags receive the highest marks for economic control of horn flies, according to Cole.

“The device does require regular attention to be effective. Regular contact with the pesticide is required with locations in gates leading to and from water, mineral or shade is helpful,” said Cole.

The insecticides used for back rubbers are usually mixed with diesel fuel, kerosene or special livestock grade mineral oil.

The latter does not evaporate as quickly and is less likely to irritate the skin than diesel. Under no conditions should cattle be allowed to use rubs that are dripping with insecticide mixes.

Face flies

“Face flies normally are a mid-summer or later problem. They’re associated with the spread of pinkeye, but they do not bite or suck blood,” said Cole.

Control of face flies is difficult. Ear tags offer the best measure available. Regular spraying or specially designed face mops, or face dusters that require almost daily use offer some control.

Other pests

Ticks typically are seen this time of year on cattle that have wintered in brushy, timbered pastures. Ticks are difficult to control unless sprays or dips are used.

“Aids-in-control statements are used on several products. Some fly tags do carry control statements,” said Cole.

Cattle grubs are not nearly the problem they were before injectable products were introduced for internal parasite control. Grubs are the result of heel flies that annoy cattle in the early spring.

Heel, stable, horseflies

The heel fly resembles a honey bee and does not actually bite cattle as it deposits eggs on the hairs of the legs.

“The fly does excite cattle and you’ll see the cattle running in the pasture this time of year with their tails twisted up over their back when the flies are laying their eggs,” said Cole.

The heel fly larva bores into the skin and migrates through the body. They will appear under the skin along the topline of the cattle as they become mature grubs, usually in January to March in southwest Missouri.

Control by spray, dip, pour-ons or injection in late summer or early fall.

“Stable flies may also present a problem on certain farms. They appear to be gaining numbers thanks to our large round bale management. They particularly like to breed in areas where hay and straw have accumulated and been tromped into the mud and manure,” said Cole.

The adult flies can cause serious gain losses on affected cattle. Sanitation is key to protecting against those losses.

Burning old hay or better yet move bale rings regularly, reduce breeding areas.

“Spraying around the source of the stable fly is suggested. Direct spraying on the cattle is viewed as inefficient. Oral larvacides are not that helpful with stable flies since they do not breed in fresh manure,” said Cole.

Horseflies also create a lot of discomfort and weight loss with their blood-sucking activities. Good horn fly control measures tend to be the most effective means of combating them.

Bottom line

The bottom line, said Cole, is that there are numerous external parasites that annoy cattle.

“Every farm has a different situation so you won’t be hit with all the pests every year. Be alert at various seasons and remember healthy, well-fed cattle can tolerate a certain level of parasites before they dig into your pocket book,” said Cole.

According to Cole, there are also research efforts to find cattle that are somewhat resistant to many of these fly pests, thanks to their genetic makeup.


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