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Parasites discussed

by Wyoming Livestock Roundup

Ostertagia ostertagi, also known as the brown stomach worm, is the most economically important parasite in cattle, according to Boehringer Ingelheim Cattle Health. In fact, the agency notes an infection can reduce weight gain in cattle by up to 20 pounds per calf and is estimated to cost the U.S. cattle industry $2 billion each year.

Life cycle

            In order to control an infestation, it is important to first understand the parasite. Therefore, Boehringer Ingelheim Cattle Health explains the lifecycle of the brown stomach worm, which begins with an adult parasite laying eggs in the gastrointestinal tract of cattle.

            Eggs are expelled from the cattle through feces, later hatching and developing into infected larvae. Boehringer Ingelheim Cattle Health notes these infected larvae then crawl into the grass cattle graze on, are ingested by cattle, and the cycle starts from the beginning.

            “Parasites like the brown stomach worm place themselves in the best position to be ingested by cattle,” explains Boehringer Ingelheim Cattle Health Veterinarian Dr. Stephen Foulke. “They try to stay at the top of the grass blades during the day and migrate back down to ground level overnight.” 

            Foulke notes several factors including stocking density and weather conditions can influence the likelihood of the cycle and consequently the number of parasites at any given time. 

            “Overgrazing pastures forces cattle to graze closer to fecal pats, placing them at greater risk of being infected,” states Boehringer Ingelheim Cattle Health.

            The agency further notes, unlike other internal parasites, the brown stomach worm penetrates the lining of the abomasum, while simultaneously harboring the ability to become dormant, which allows the next generation to survive during extreme hot or cold. 

            “When conditions improve, the larvae can emerge all at once, causing severe inflammation and irritation, reduced feed intake and sometimes even death,” says Boehringer Ingelheim Cattle Health.

Management strategies

            “Producers often ask about the best deworming protocols, but unfortunately the answer is different for every operation,” says Foulke, noting deworming programs are going to differ between a cow/calf herd in Wyoming and a stocker operation in Florida.

            However, regardless of the operation type, Foulke reminds producers it is always important to ensure their deworming products are stored correctly and the doses they administer are accurate for the weight of the animal being treated.

            “A common practice is to dose dewormers according to average weight of the herd. While convenient, this can over or under dose a significant number of cattle and diminish the effectiveness of the drug,” explains Boehringer Ingelheim Cattle Health. 

            Therefore, the agency suggests operations invest in a scale, which can more accurately determine dosages and reduce product waste. Boehringer Ingelheim Cattle Health also encourages producers to seek assistance from their local veterinarians in order to determine parasite load on their operations and effectively manage brown stomach worms in their cattle herds.

            Hannah Bugas is the editor of the Wyoming Livestock Roundup. Send comments on this article to        

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