A fence for cows on the American farm. Author: kavaram

Practical Parasite Control and Prevention of Resistance

Julia Herman, DVM, MS Beef Cattle Specialist Veterinarian, NCBA, a contractor to the Beef Checkoff | July 19, 2022


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Summer brings new challenges to the cattle herd as temperatures and humidity increase. One influence of this weather change is parasite growth and its potential effects on all classes of cattle. Parasite management does vary by region with differences in climate, environmental conditions, host susceptibility, and farm/ranch management practices. With proper nutrition and grazing management plans, many parasites can be controlled through environmental management. What does not vary by region is anthelmintic resistance, where internal and external parasites have developed resistance to the animal health products and dewormers readily available for parasite control.


Anthelmintic resistance has been recognized in small ruminants for many years, but the beef industry is not immune. Resistance in intestinal worms of cattle have been documented for over twenty years1. John Gilliam, associate professor and clinical veterinarian at Oklahoma State University realizes the beef cattle industry needs to recognize that anthelmintic resistance is present and is becoming more of concern. Anthelmintic resistance has been documented in multiple parts of the United States, not just the Southeast region2

Promotion of resistance comes from misuse of the products available. There are a few common ways that misuse could occur: 

  • When groups of animals are dosed to the average weight of the group, the heavier animals are likely underdosed, meaning worms are not completely killed and resistant worms have a higher chance of surviving.  
  • Certain products, like pour-on dewormers, may increase resistance more than other products due to underdosing or inappropriate application (i.e., not applying along the back from head to tail). Squirting cattle with dewormer as they run by is a great way to waste product, waste money, and increase anthelmintic resistance.  
  • Using anthelmintic products for parasites not on the label, such as using a dewormer for flies. The Environmental Protection Agency has specific labels and regulations for each topical anthelmintic. Be sure to read the label of each product and use it for its intended parasite. 

Preventing resistance in the animal health realm can apply to both antimicrobial and antiparasitic products. Because of anthelmintic resistance, treatment protocols have become more complex than giving a single product and necessitate veterinary consultation. As discussed in the Beef Checkoff-funded Beef Quality Assurance (BQA) Program, proper dosing to bodyweight of the animal plays a role in effectiveness of the medication. While much focus is placed on withdrawal times for antibiotics, do not forget that many topical and injectable parasite treatments have withdrawal periods to adhere to. Beyond anthelmintics, which can be very effective when used properly, alternative methods to managing internal parasites can be effective adjunct strategies.  

To effectively treat or control parasites in the herd, it is important to know exactly which ones are a problem. This can be challenging at times, so it is critical to have a resource team ready to assist. Working with your local veterinarian and extension agent will help tailor a strategy to the specific operation, using multiple modalities to protect your herd. Coordinating with neighboring ranches on parasite control would also improve overall success of the program. 

Every producer has a parasite control program but may not be assessing the efficacy of their program. Gilliam reminds producers there is no way to know if your herd has resistance without looking for it. This is where the Fecal Egg Count Reduction Tests (FECRT) can play a key role3. These tests can be run as a screening test with the help of your veterinarian and are designed to measure the efficacy of the anthelmintic treatment.  

The FECRT requires a sampling of a group of animals at the time of treatment followed by a second sampling 10–14 days after treatment2. This test can be used for any oral, injectable, or pour-on anthelmintic products. Labor and cost will need to be evaluated for each operation since cattle will need to be handled at least twice for sample collection and potential treatment. Testing around 20 randomly selected animals within the herd has been shown to be a representative sample for detecting resistance at the herd level. If a herd has less than 20 animals, all of the would need to be tested.  

Another way to monitor, Gilliam adds, is completing routine surveillance of fecal samples which can be a strategy to count the number of parasite eggs to see if deworming is needed for an individual animal. Different diagnostic laboratories and veterinary clinics will use different tests for determining fecal egg counts, so it is important to plan ahead and have that conversation before collecting samples. Some laboratories will accept composite sampling, which means combining multiple samples into one sample in a standardized manner, which can save on costs. Parasite control programs, whether completing surveillance or treatment, can be complicated to develop so working with your herd veterinarian is vital.  

Parasite prevention programs are an essential part to the herd health plan and should be re-evaluated on an annual basis. The significance of considering the cattle’s entire environment – from optimizing nutrition, having a solid herd health program, using low stress handling, etc. to provide the foundation for a strong immune system and healthy cattle – cannot be emphasized enough. Reviewing the BQA principles will help cattle producers focus on these preventive practices that will improve animal health, optimize productivity, and reduce management costs. 

1 Gasbarre 2014. Anthelmintic resistance in cattle nematodes in the US. Vet Parasitology 204 (2014) 3-11. https://doi.org/10.1016/j.vetpar.2014.03.017 

2 Gasbarre et al. 2015. Effectiveness of current anthelmintic treatment programs on reducing fecal egg counts in United States cow-calf operations. Can J Vet Res (2015) 79:296-302. PMID: 26424910; PMCID: PMC4581674.  

3 American Consortium for Small Ruminant Parasite Control. Fecal egg counting. https://www.wormx.info/fecal-egg-counting. (Accessed June 9, 2022). 

 This article was originally published in the July 2022 issue of NCBA’s National Cattlemen newspaper.