In the 1960s, deworming was done by a veterinarian, who treated a horse by passing a stomach tube through his nose to deliver potent chemicals that killed everything that wiggled. Horses hated it, and so did owners.
It was considered a breakthrough when owners were able to avoid the stomach-tube experience by simply squirting gooey, over-the-counter deworming paste into their horses' mouths.
By the 1980s, more was known about parasite life cycles, and owners began faithfully following recommendations to administer medications on a six-to eight-week schedule.
If you're still following that or certain other protocols from that time, guess what? This is 2010. After the passage of decades, much more has been learned about equine parasites and how to control them.
As a result, owners are now being urged to make another change in how they think about and approach parasite control. The change is considered so important by the veterinary community that it's been addressed at the last several American Association of Equine Practitioners (AAEP) conventions.
The new protocol relies heavily on fecal-egg-count testing. You'll read more about that here. I've been helping my own practice's clients understand and adjust to the recommended new protocol, and now I'll pass the info on to you.
The goal: to keep you as up to date as possible on ways to protect your horses' health from the damages of internal parasites.
Change of Enemy
Common (older) plan: You've been deworming your horses every six or eight weeks. To help yourself stay on schedule, you may deworm each time your farrier comes to trim or shoe.
What's new? Over the years, shifts in the parasite populations have changed the way these pests respond to medications. In the past, the large strongyle was an owner's most serious concern. But in recent years, the small strongyle and the tapeworm have emerged as more significant threats.
Trouble is, the six-to-eight-week-interval deworming programs of years past were designed around the life cycle of the large strongyle—no longer the most important enemy in our war against worms.
Even more important, widespread and frequent use of deworming drugs has led to resistance within some parasite populations. While the drugs ivermectin and moxidectin remain effective against most parasites, and although praziquantel is still effective against tapeworms, overuse of these or other deworming agents risks further resistance. If we're not careful, we could be left without an effective parasite-control weapon.
What to do: It's now recommended that you deworm only when it's necessary—and with a medication that's effective against the right worms. This minimizes pressure on the remaining effective deworming medications, and ensures they continue working. With this protocol, your basic plan would be to deworm only twice a year, with fecal egg counts used to determine whether more frequent dewormings are required.
Common (older) plan: You've been rotating dewormers frequently to avoid resistance. This plan also allows you to take advantage of feed store or catalog sales.
What's new? Resistance to various deworming medications has become widespread. If you conduct random rotation of deworming medications based on what's on sale, you could be treating your horse ineffectively—thus putting him at higher risk for parasite-related health problems. If you're treating a group of horses in a barn or pasture, in-effective deworming means more eggs shed on the pasture, and an escalation of parasite burdens, even in less susceptible horses.
What to do: Use fecal egg counts to monitor the efficacy of your deworming program. There's no real need to rotate, as long as you're testing to determine whether resistance is an issue. But if you discover you have a resistant population of parasites to a specific dewormer, that dewormer should no longer be a part of your parasite-control strategy—even if it's on sale!