Why Doesn’t My Dewormer Work?

It’s easy to question the need for deworming. The damaging effects and severity of internal and external parasites are hard to see with the naked eye — especially when compared to other diseases that have obvious clinical signs. What you can’t dispute, though, is the years of research that underline the fact that parasites will rob your herd of profits.

Don’t assume that just because you’re deworming cattle with a product labeled to control internal and external parasites that you are 100 percent covered. Dr. Mac Devin, a Professional Services Veterinarian with Boehringer Ingelheim Vetmedica, Inc., says producers need to understand these products aren’t created equal and understanding these differences will help you effectively fight parasites.

Two different families 

Endectocide parasite control products fit in the broad category of chemicals known as macrocyclic lactones. Macrocyclic lactones are then broken-down further into two categories: avermectins and milbemycins.

Both of these groups have their own chemical structure and thus, behave differently when used for internal and external parasite control. “Avermectins include ivermectin, eprinomectin, abamectin and doramectin; milbemycins, a different molecular structure, has moxidectin,” explains Dr. Devin, when discussing the most common active ingredients found in parasite control products.

Dr. Devin says the structural differences of Milbemycins change the distribution of the drug in the animal. “Moxidectin, the active ingredient found in Cydectin®, has a much greater affinity for fat than other macrocyclic lactones.” “This affinity for fat means that the active ingredient will stay around longer,” says Dr. Devin. He adds, “This longer duration allows Cydectin to have greater persistency against some species of internal parasites.”

Dr. Devin references research conducted at Louisiana State University that compared the growth performance and persistent activity of the active ingredients. These trial results concluded that cattle treated with moxidectin achieved the greatest weight gains by the end of the study. Further, egg counts and percent reduction in egg counts were greater in moxidectin-treated groups than those treated with doramectin and ivermectin.1

Work gone to waste? 

The type of formulation utilized for animal administration may also make a difference in efficacy. The common formulations include injectables, pour-ons and drenches. Pour-ons can offer ease-of-use but many fear their efforts can go to waste in the event of rain. Dr. Devin says that’s where a lipid based pour-on formulation, as opposed to alcohol-based, can really be valuable. “Cydectin, being lipid-based, won’t wash off in the rain like alcohol-based pour-ons — it’s rain fast,” says Dr. Devin.

A research trial measured the lasting effects of Cydectin Pour-On after a simulated rain shower. After administering Cydectin Pour-On at the label dose, 48 cattle were exposed to simulated rainfall at 2 inches per hour at 2-, 6-, and 24-hours post treatment. Fecal egg count data was then collected on all groups. The data showed that efficacy was not impaired by the rain event when compared to control cattle.2 Additional research showed that at six hours post treatment, less than 2 percent of Cydectin Pour-On had washed-off.3

Dr. Devin recommends that producers work with their herd veterinarian to develop a parasite control program that works for their operation, and discuss the product types and formulations available.

Boehringer Ingelheim Vetmedica, Inc. (St. Joseph, MO), is a subsidiary of Boehringer Ingelheim Corporation based in Ridgefield, CT and a member of the Boehringer Ingelheim group of companies.

The Boehringer Ingelheim group is one of the world’s 20 leading pharmaceutical companies. Headquartered in Ingelheim, Germany, it operates globally with 145 affiliates and more than 42,000 employees. Since it was founded in 1885, the family-owned company has been committed to researching, developing, manufacturing and marketing novel products of high therapeutic value for human and veterinary medicine.

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1J.C. Williams et al., Veterinary Parasitology 85 (1999) 277-288

2 Fort Dodge Animal Health, new animal drug application, NADA 141-099, FOI Summary,
experiment B-92-13

3Fort Dodge Animal Health, new animal drug application, NADA 141-099, FOI Summary,
experiment B-US-4-95

Cydectin is a registered trademark of Boehringer Ingelheim Vetmedica, Inc. Ivomec and Eprinex are registered trademarks of Merial, Dectomax is a registered trademark of Pfizer Animal Health.