The risk of deworming by rotation drives change

Dr. Tony Hawkins Valley Vet Supply

While word can travel fast, change can sometimes happen a little more slowly. This is the case with rotational deworming – an outdated approach that is still used, though less so than studies indicate.

The rotary deworming approach dates back more than 40 years. The thinking at the time was that horses should have zero parasite eggs in their faeces. So the owners incorporated deworming every 60 days, using a different deworming product each time. An effective approach then decades later created parasite resistance in horses; the practice inadvertently selected for parasites resistant to every deworming treatment.

When dewormers came out, they worked well against everything. We managed to deworm every animal with great success. But since then, with the introduction of rotational deworming practices, small strongyles have grown to become the bigger problem. They develop resistance more easily. To avoid contributing to additional resistance, deworming recommendations had to be changed.

The American Association of Equine Practitioners’ Parasite Control Guidelines—an important resource for horse owners to review and discuss with veterinarians—states, “The true goal of parasite control in horses (and other equids) is to limit parasite infections so that the animals remain healthy. and clinical disease does not develop.”

The goal is not to eradicate all parasites from a given individual. Appropriately timed treatments with effective anthelmintics – given at the right time of year – are needed to match epidemiological cycles of transmission and relative parasite burdens in individual horses.

Discuss the end of rotational deworming

After learning that a trainer, barn manager, or riding friend is still consistently following a rotational deworming program, consider the best way to start a conversation. Start by asking why I think rotational deworming is a good idea—and know that “because that’s the way we’ve always done it” is probably not the best answer anymore.

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If she or he is open to having a discussion, follow up with, “Recent work has shown that rotational deworming promotes resistance to these parasites. To ensure long-term success with our deworming program, we may want to consider doing fecal egg counts and deworming horses more selectively based on the results. This will mean less dewormers to buy and give an idea of ​​the parasite population on the farm. It gives us a lot of information. And at the same time, it allows us to worm the horses at the frequency that they really need to be wormed and with the appropriate products that we need to use.”

American Association of Equine Practitioners guidelines recommend deworming when parasite levels may be highest, during the spring and fall. The bot and tapeworm treatment should be timed to coincide with the end of the bot fly season and the end of the tapeworm pasture season, usually in late fall or early winter.

For puppies, I recommend deworming every two months until they are one year old. Foals are prone to roundworms from the start; Benzimidazole dewormers – also known as “white dewormers” – are recommended. Yearlings and two-year-olds should be dewormed an average of three to four times a year – based on faecal egg count results – with either ivermectin or moxidectin and praziquantel for tapeworm control in the fall.

As a general practice, adult horses should be treated twice a year, during spring and autumn. Adult horses should be dewormed with either ivermectin or moxidectin and praziquantel for tapeworm control in the fall.

Many older horses become heavy feeders as they age, which is to be expected due to decreased immunity. It’s ideal to treat them like a normal adult horse – do a faecal egg count and worm them two to four times a year based on that.

A Fecal Egg Count Reduction Test Ask a veterinarian about doing an annual fecal egg count, which will help guide the frequency of deworming treatments a particular horse needs. Perform a fecal egg reduction test on both foals and adult horses every two years. In herds with a large number of horses, it is not necessary to perform a faecal egg reduction test on all horses; six is ​​the recommended number.

Always dose dewormers to the actual weight of the individual horse. Many horse owners do not; they just give it their all. They think “If less is better, more is better, right?” It is important to weigh them or use a weight tape to dose accurately.

Talk to a veterinarian for more information tailored to your horse’s individual needs.

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Dr. Tony Hawkins is a technical service veterinarian for Valley Vet Supply. He attended Kansas State University-College of Veterinary Medicine where he focused on mixed animal practice. Prior to joining the veterinary team at Valley Vet Supply, Hawkins practiced veterinary medicine in Marysville, Kansas, where he was involved in cattle health – including processing, obstetric work and serving the local sale barn. He is valued by the community for caring for horses and pets through wellness appointments and surgeries.

Valley Vet Supply was founded in 1985 by veterinarians to provide animal health solutions to clients. Drawing on more than half a century of experience in veterinary medicine, Valley Vet Supply serves equine, pet and livestock owners with thousands of products and medications selected by Valley Vet Supply’s Technical Service veterinarians and team of professionals from industry. With an in-house pharmacy that is licensed in all 50 states and verified through the National Association of Boards of Pharmacy, Valley Vet Supply is your go-to source for equine, livestock and pet supplies. Visit for more information.

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