Still On a Rotational Deworming Schedule? Check This Out

It’s now widely realized by most veterinarians and horse owners that rotational deworming is no longer the best practice for long-term parasite control. This visual should help show why.

As a relatively recent convert to the fecal egg count and targeted deworming strategy, I realize that I may be preaching to the choir — but for any readers who haven’t switched to this deworming method and are curious to learn more, I hope this article helps illustrate why rotational deworming should be rotated right out of practice.How does a fecal egg count work?

The process is fairly simple: a fecal sample is gathered and a specific weight or volume of the sample is mixed in a flotation solution, then examined under a microscope. The eggs of parasites in the intestinal tract are then counted and the veterinarian or lab technician can then calculate how many eggs per pound of manure are generated by the individual horse and by which types of parasites. The veterinarian can then develop a targeted deworming program with the owner to specifically work on the parasites each horse contains.

Ideally, a fecal egg count (FEC) is paired with a fecal egg count reduction test (FECRT) — the second test is taken 10 to 14 days after the horse is treated with the targeted deworming product to make sure that the product was effective. If you can only test once, test prior to deworming. Samples should be tested in the spring before horses are turned out on pasture and again in the fall.

The FEC measures the amount of eggs shed by a horse — which is not necessarily to say that the horse is “infested with worms.” A high shedder can and most likely will continue to look like a healthy horse at good weight with a shiny coat, all the while he continues to shed a high amount of eggs into his pasture to be picked up by his herdmates.

But rotational worming has worked for so long. Why shouldn’t we keep using rotational products?

Rotational worming — the traditional method in which horses are treated every two months or seasonally with a different class of dewormer — worked when over-the-counter deworming pastes first came on the market. However, the biggest threat has changed from large to small strongyles, and many parasites are now developing resistance to dewormers thanks to a constant use of these products. Targeting a deworming program for the type of parasite and amount of eggs shed can help prevent the over-use of medicines and increase the overall health of a herd and pasture. It also makes sure that owners are treating with the correct dewormer — not using a product that doesn’t even target the kind of parasites the horse might carry.

My horse looks healthy and he’s been on a rotational plan. Why change?

A fat, happy and shiny horse can still be a high shedder, and is continuing to release eggs into the pasture. All a rotational product does is band-aid the problem for a few months, rather than manage the parasites in a targeted fashion.

Here’s a visual that really drove home the point for me: I’ve been using a free traveling clinic that comes to our area in the fall and the spring to have fecal egg counts performed. I followed the attending veterinarian’s fall protocol with my six horses, and this spring got my father-in-law on board with his four horses, who live on a separate farm just a mile or two down the road.

My father-in-law’s horses, wormed with on rotation, are the first four horses on the list photographed below (Randy black, Chuck, Derek and Tyrone). My six horses follow after that (Winston, Red, Randy brown, Dutch, Skip and Rocky). Note the difference in egg counts after just one rotation of the prescribed protocol versus a rotational program:

Photo by Kristen Kovatch.

Seeing these figures side-by-side like this really drove the point home for me: what a difference can be made by changing tactics. Change can be hard, but it’s important to make these decisions based on what is truly best for your horses’ health.

Parasites can live in pasture for a long time — the presiding veterinarian told me up to a year; some sources state as long as a decade. It’s important to manage manure at home as much as it is to target the dewormer, but now both of our farms are on their way to managing parasites from an evidence-based perspective rather than long-standing common practice.

Further reading:

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