The brown stomach worm (here a male and female) are one of the most important parasites in cattle. (Photo courtesy Dr. Tom Yazwinski, University of Arkansas, Fayetteville)
The brown stomach worm (here a male and female) are one of the most important parasites in cattle. (Photo courtesy Dr. Tom Yazwinski, University of Arkansas, Fayetteville)

Although specific estimates are not available, economic losses from worm parasite infections of cattle can be significant.

The extent of internal parasite problems is usually related to management practices that increase exposure, whereas ongoing preventive management practices will minimize losses caused by parasite infections.

Calves under one year of age are more susceptible than older cattle. Older cattle frequently have been exposed to the parasites and developed a degree of immunity, but the cow herd remains the major source of initial exposure of the calves.

Adult worms in the gut of cattle produce eggs that are passed in the feces. The eggs hatch, producing immature larvae that develop and move up onto the pasture grasses.

Infective larval forms of the worms may be present in large numbers on the growing forage. Some of the eggs can survive the winter and hatch out with warm weather.

Temperatures between 60° and 80°F and at least 2 inches of rainfall per month provide excellent propagation conditions. Feed bunks or waterers contaminated with feces can be a source of exposure to the larvae.

The need to deworm calves during the summer depends strictly on the degree of contamination of pastures or lots. Use of the same pastures year after year or high densities of grazing cattle can result in heavily contaminated forage. The number of times calves should be wormed during the spring and summer depends on the level of exposure and reinfection.

Deworming cattle when they enter a feedlot is cost-effective only if the parasite load they are carrying is great enough to reduce the rate of gain. The decision to deworm cattle can be based on finding large numbers of worm eggs by microscopic examination of feces (fecal egg counts).

Alternatively, cattle from the Southwest can generally be expected to have a heavier load of parasites than Western cattle. The parasite load of cattle from the Midwest will be variable.

Internal parasites have the greatest impact on rate of gain when cattle are on low energy levels, which are typical of receiving or backgrounding rations; therefore, deworming feedlot cattle when they are processed into the feedlot will give the best returns.

One of the most important parasites in cattle, the brown stomach worm, lives in the abomasum, the true stomach.

These worms are active during the grazing season, busily laying eggs. At the end of the grazing season, developing fourth-stage larvae (L4) bury themselves in the glands of the stomach and are dormant until spring when they emerge, become adults and start egg laying. Because of this, it is recommended that adults be removed to reduce the abomsasitis and that L4s be removed to minimize glandular damage and exposure to parasites in the spring.

Timely, “strategic” deworming prior to the grazing season will greatly reduce the subsequent contamination of pastures during the grazing season.

Pregnant cows can be dewormed in the fall. These cows can be expected to winter better, have a higher conception rate the next breeding season and wean heavier calves.

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