An abundance of rainfall in Arkansas has created ideal conditions for the development of internal parasites of cattle, according to Tom Troxel, animal science section leader for the University of Arkansas Cooperative Extension Service.

“Throughout the early summer, most of Arkansas has received an above-normal amount of rainfall plus cooler-than-normal temperatures,” Troxel said. “This weather is favorable for growing grass for pastures and hay, but it also favors the life cycles of internal parasites that infect cattle.

“Because of these conditions, internal parasites or worms that infect beef cattle are probably more numerous and more active than normal.”

The effect of internal parasites in cattle vary with the severity of infection as well as age, nutritional status and stress level of the animal, Troxel noted. Usually, younger animals are most adversely affected. Parasites can cause reduced weight gain, roughness of coat — which can affect selling price — anemia, diarrhea and lowered feed efficiency.

Troxel said roundworms are considered the most economically devastating internal parasites of Arkansas beef cattle. Roundworms such as the brown stomach worm can be in an active or inactive, or inhibited state, during summer. Inactive roundworms are a concern because they too have likely increased in numbers, according to Troxel.

The major impact of inactive worms will be in mid-August, said Troxel. That's when they become active, further debilitating cattle and increasing contamination in pastures through their feces.

“When cattle graze, they pick up the parasites from contaminated pastures,” he said.

Troxel recommended that cattle producers consider deworming their replacement and growing stock during midsummer.

Tom Yazwinski, University of Arkansas professor of animal science, said an effective treatment for inactive parasites is a macrocyclic lactone product.

“That means the active ingredient in the dewormer should be an ivermectin, doramectin, eprinomectin or moxidectin. These ingredients provide excellent control of both active and inactive forms of internal parasites. By treating the cowherd in July with one of these medications, the active and inactive internal parasites will be killed, which will, in turn, reduce pasture contamination for the late summer and early fall.”

When you select an animal health product, be sure to read the label and select the product that is approved for the type of animal being treated. Always read and follow the instructions, Yazwinski said.


Lamar James is an Extension communications specialist with the University of Arkansas.