Five Myths of Internal Parasite Control

Identifying the misunderstandings of parasite control

It’s estimated that the cattle industry loses about $3 billion each year in lost weight gains, poor feed conversion and increased disease because of internal parasites.1 With the financial impact and animal welfare concerns on cattle operations, it is important for producers to understand parasite control, as well as the misconceptions about parasite control.

Here are five parasite control myths that might be putting a producer’s management program at risk.

Myth No. 1: All active ingredients in parasite control products have the same efficacy.
There are different active ingredients and different classes of dewormers, which should be used strategically on an operation for effective parasite control, advises Mark Alley, DVM, managing veterinarian with Zoetis.

Products such as DECTOMAX® Pour-On or DECTOMAX® Injectable provide both extended therapy and good efficacy against both adult and inhibited Ostertagia, the brown stomach worm. However, in populations of cattle where Cooperia, Nematodirus or Haemonchus are an issue, white dewormers such as VALBAZEN® Suspension may be a better selection. It is important that a producer has a discussion with his or her veterinarian or animal health provider to determine which is most appropriate.

Myth No. 2: My animals look fine, so I don’t have a parasite resistance problem.
“Parasitologists agree that no dewormer provides 100% effectiveness against parasites,” said Dr. Alley. “We make the assumption that all parasite control products are 100% effective, but even with 50% kill of parasites, producers will see a clinical improvement in the animals.”

Dr. Alley says producers can’t tell visually if there is a resistant parasite problem in the herd. They need to work closely with their veterinarian to diagnose resistant parasites and establish a strategic deworming program.

Myth No. 3: Parasites cannot withstand winter’s cold temperatures.
“It is a mistake to think it gets cold enough to kill parasites over the winter,” Dr. Alley said.

Parasites can simply overwinter in cattle or pastures. While winter may take its toll on many things, studies demonstrate that infective larvae were able to survive on pastures during winter months.2,3

Myth No. 4: Antiparasitics can be administered to work at a producer’s convenience.
Timing is critical for administering antiparasitic products. Often, producers deworm when it’s most convenient for them, rather than when it’s most effective to control parasites. Dr. Alley recommends year-round parasite control, both in the fall and again in the spring before summer pasture turnout.

Myth No. 5: Dosing to the average weight of the group is adequate.
It’s important for producers to not only match the dewormer to the type of parasite challenge but also to administer each dose per the animal’s calculated weight. Incorrect dosing has been identified as a major contributor to the development of resistant parasites. A common practice is to dose products to the average weight of the herd, rather than to the individual weight of the animal. In this case, half the herd could be underdosed.

For more information about parasite control, please visit with your animal health adviser or Zoetis representative.

DECTOMAX Injectable has a 35-day pre-slaughter withdrawal period. DECTOMAX Pour-On has a 45-day pre-slaughter withdrawal period. Do not use in female dairy cattle 20 months of age or older. Do not use in calves to be processed for veal. DECTOMAX has been developed specifically for cattle and swine. Use in dogs may result in fatalities.

Cattle must not be slaughtered within 27 days after the last treatment with VALBAZEN. Do not use in female dairy cattle of breeding age. Do not administer to female cattle during the first 45 days of pregnancy or for 45 days after removal of bulls.

About Zoetis
Zoetis (zô-EH-tis) is the leading animal health company, dedicated to supporting its customers and their businesses. Building on more than 60 years of experience in animal health, Zoetis discovers, develops, manufactures and markets veterinary vaccines and medicines, complemented by diagnostic products and genetic tests and supported by a range of services. Zoetis serves veterinarians, livestock producers and people who raise and care for farm and companion animals with sales of its products in more than 100 countries. In 2015, the company generated annual revenue of $4.8 billion with approximately 9,000 employees. For more information, visit

For more information, contact:
Leona Ling Ferguson

Aimee Robinson
Bader Rutter

1 Bagley C, Healey MC, Hansen D. Beef Cattle Handbook: Internal parasites in cattle. Accessed October 24, 2016.
2 Tritschler J. Internal Parasite Control in Grazing Ruminants. Petersburg, VA: Virginia State University.
3 Smith HJ, Archibald RM. On the Survival of Overwintering Bovine Gastrointestinal Nematode Larvae During the Subsequent Grazing Season. Can J Comp Med. 1969;33(1):44-47. Accessed October 24, 2016.



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