Test the Effectiveness of Dewormers

April 5, 2019



Help producers get the best results from their dewormer purchase.

“How do I know if my dewormer is working?” That’s a million-dollar question, according to Doug Ensley, DVM, technical marketing manager at Boehringer Ingelheim.

To test the effectiveness of your dewormer product, Ensley recommends that producers work with their veterinarian to perform fecal egg count reduction tests (FECRT). 

FECRTs assess the effectiveness of products being used and can help detect if producers have parasite resistance in their herd. Begin by taking two sets of fecal samples:

Sample 1: At the time of treatment, or according to the veterinarian’s recommendation. Be careful to dose the animal correctly. Underdosing can show resistance when it may not exist.

Sample 2: 14 to 28 days later (depending on the treatment dewormer), from the same animals.

Image of Dr-Doug-Ensley
Dr. Doug Ensley

“Do this test on 20 percent of your herd, or 20 animals, whichever is fewer,” Ensley says. “Then, count the reduction in egg counts. We want to see a 90-to-95 percent fecal-egg-production reduction.” Less than that would suggest a resistant population is present.

From there, a veterinarian can help producers determine the predominant worm species present in the herd and the right dewormer to ensure the herd is protected. 

“Cattle can be exposed to parasites much longer than the 14 to 42 days of protection offered by conventional dewormers. This means herds can go through grazing season with little protection against parasites.”

Resistance is not a common problem across the country, but it can vary from herd to herd based on the location and deworming practices, Ensley says. 

It is likely resistant parasite populations are present in herds that don’t use dewormers according to the product label or don’t focus their efforts on proper management practices. Operations that often apply dewormers off label for fly control are also more likely to have resistance issues.

Spring deworming is critical

In most parts of the country, spring is when the highest parasite load on the pasture – and in the animal – will occur. 

The most economically important parasite, Ostertagia, overwinters in the animal. In the spring, this parasite becomes an adult and sheds eggs on pasture. Other parasites overwinter in the soil and fecal pat then begin to become infective in the spring.

“Spring deworming will help fight off this new contamination,” Ensley says. “It’s also, for a large part of the country, calving time. This will be when the parasite can inflict the most damage to the cow. We want the cow to be as clean as possible to help her milk and produce a great calf. This gets her ready to breed and reduces the impact of parasites on breeding. We also want to reduce contamination to give the newborn calf the greatest opportunity for reaching its genetic potential.”

Distributor support

Distributors can help support their producers and veterinarian customers in the FECRT process. If a producer would like to perform a test, distributors can connect with their local manufacturer sales representative.  

FECRTs aren’t complicated or costly and provide an opportunity to build trust with a customer, Ensley notes. 

“As the distributor rep builds confidence in the customer, more products will be sold,” he adds. “The customer is also going to benefit by getting healthier, stronger calves, which will put more money in their pocket. Teaching the client about proper dewormer management practices will help the product perform at its highest efficacy and be a product that the distributor can continue to sell.”

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