As more cases of parasite resistance are documented in our country’s beef herds, industry experts are finding management inspiration in their crop protection counterparts’ resistance management playbook. Refugia, multiple modes of action, pest identification, application timing and use rates are cornerstones to managing resistant pests in crops, and those principles can be applied to the beef industry, as well. Of those principles, refugia may be the biggest game changer.

“A study¹ in Georgia looked at 12 cow-calf operations and saw resistance in 11 out of the 12 operations,” explained Jody Wade, DVM, Boehringer Ingelheim. “The only farm that didn’t experience resistance was a farm that was incorporating refugia into their deworming program.”

The concept of refugia is grounded in leaving a population of parasites unexposed to the dewormer treatment to slow down the development of resistance. “The biggest concern we’ve received from producers about leaving a group of cattle untreated is that they’re not going to gain weight like the calves we treated because parasite issues can decrease weight gain,” Dr. Wade reported. “But we haven’t seen a significant negative effect in the studies² we’ve done so far. The refugia calves have done as well as the calves we’ve dewormed.”

Choosing refugia candidates

Dr. Wade pointed out that choosing the right animals to leave as refugia makes a big difference. “Choose the biggest, heaviest, healthiest ones that don’t look like they have parasite pressure,” he advised. “The ones that are thin and unthrifty, you definitely want to deworm them.”

Christine Navarre, DVM, MS, DACVIM, extension veterinarian with the Louisiana State University AgCenter, agreed, and added there are many variables to consider when adding refugia to a management program.

“A lot of it starts with the animals and using data,” she said. “One thing we need producers to do is take fecal egg counts throughout the season and at different ages to better understand the dynamics within their herd.”

Fecal egg count tests are the window into understanding which parasites are present in a herd and at what levels. Initial tests should be followed by fecal egg count reduction testing 14–21 days after administering the dewormer treatment to gain visibility into the effectiveness of the protocol.

“Take fecals and look at the parasite load,” Dr. Wade stressed. “If those cattle have a heavy parasite burden, then we know we need to reassess our deworming program.”

Consider contributing stressors

Dr. Navarre likes to include a grazing specialist and/or nutritionist when creating a refugia and parasite management program because nutrition and pasture management are also critical factors. “We don’t want parasites to take advantage of other stressors, so we want to manage pastures for the health of the grass and nutrition of the cattle,” she explained. “If cattle stay in good shape nutritionally, that helps keep parasites that are on pasture from impacting cattle as much. And it allows us to utilize a more aggressive refugia program.”

Generally, the refugia target is 10% of the herd, and Dr. Navarre emphasizes using data, particularly fecal egg count reduction tests, in determining the right refugia target for your operation.

In addition, she and Dr. Wade advise administering a combination of products from different classes of dewormers, rather than switching to a different class of dewormer each time you treat your cattle. “Using the same product over and over again can open the door for more parasites to survive,” said Dr. Wade. “By administering dewormers from different classes, you target parasites in different ways — reducing the risk of developing parasite resistance in your herd.”

Incorporate other important practices

Beyond implementing refugia and treating with more than one class of dewormer, other critical components of a successful parasite management program include:

Creating an effective parasite management program involves melding many variables into a cohesive, holistic protocol grounded in data specific to your operation. Taking a page from the crop protection resistance management playbook by incorporating practices like refugia, multiple modes of action, timing and use rates can help fend off resistant parasites and set up your herd for a more sustainable future.

¹ Paras KL, George M, Howell S, Collins J, Storey BE, Kaplan RM. Prevalence of gastrointestinal nematode resistance to avermectin anthelmintics on beef cattle operations in Georgia. American Association of Veterinary Parasitologists Conference 2017. Available at: https://www.academia.edu/80467725/Prevalence_of_gastrointestinal_nematode_resistance_to_avermectin_anthelmintics_on_beef_cattle_operations_in_Georgia?f_ri=657

²Kipp K, Cummings DB, Goehl D, Wade HH, Davidson JM, Renter D, Verocai GG, Rash L. Evaluation of a refugia-based strategy for gastrointestinal nematodes on weight gain and fecal egg counts in naturally infected stocker calves administered combination anthelmintics. Veterinary Parasitology, Volume 319, 2023, 109955, ISSN 0304-4017. Available at: https://www.sciencedirect.com/science/article/pii/S0304401723000869?via%3Dihub

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