Despite the fact that deworming is such an economically sound practice, nearly 40 percent of cow-calf operations only treat their cows once a year. While the belief may be that this saves on treatment input costs, choosing not to deworm could, in fact, potentially cost producers as much as $200 per head per grazing season.

To achieve an optimal return on investment, producers need to take several factors into consideration, including how long a product works and which parasites it treats, timing and pasture management to avoid recontamination of the grazing land.

Joe Dedrickson, DVM, Merial Veterinary Professional Services, says that it is a common misperception that parasite control products protect cattle against parasites for the entire season. “Most products work, on average, 14 to 28 days, depending on the product and the parasite. White drenches and pastes kill only what is present in the animal at treatment with zero persistency,” Dr. Dedrickson says.Studies show that there needs to be persistent parasite control for at least 100 days to break the parasite life cycle. Thus, one fall or spring deworming will simply not provide seasonal protection in your herd or on your pasture and opens up your operation to continual parasite reinfection.

According to a strategic deworming study, timing is also critical to the success of any deworming program. 8 It states that, “It is important not only to treat when cattle are worked, but to time treatments to kill these parasites before they have time to develop into an adult parasite, producing eggs within the animal, which could lead to reinfection.”

Because every producer’s situation is unique, Dedrickson recommends consulting with your veterinarian when developing a deworming strategy, and suggests keeping the following in mind: “The time of year when grazing season begins, age and category of the animals, type of operation and grazing history of the pasture are all considerations to discuss.”