Ascarids, Strongyles, and Bots, oh my!

For horse-owners, spring means lots of things. Trails that were closed or impassable due to mud are open. The days are longer. Grooming chores are more intensive for a while, until all that winter hair sheds out. And it's time to think about worming, vet check-ups, and vaccinations, yet again. Because horse-owners just aren't happy unless we're obsessing over our equine pal's coat, weight, condition, and poop. As disgusting as it sounds to non-horse-owners, and to the inexperienced horse-owner, those piles of manure you clean out of his stall every morning can tell you a tremendous amount about his health and well-being, and you need to pay attention to them. For example, in especially bad parasite-infestations, those fecal balls may have actual worms in them. Horses that look quite wormy, thin with pot-bellies

When we worm our horses in the spring, we're primarily concerned with some specific varieties of parasites. As well, we're specifically interested in the life-stage of those parasites, because we have to worm our animals in a targeted fashion to design an effective worming program. Horses typically have to deal with tapeworms, bots, strongyles, roundworms (ascarids), hookworms, pinworms, lungworms, threadworms, and probably a few more varieties that I've forgotten to list. That sounds like a lot, I know, but the basic types of commercial horse-wormers available will effectively combat all those kinds of parasites: moxidectin, ivermectin, fenbendazole and mebendazole, praziquantel, and pyrantel pamoate. So most of the horse-owners I know have adopted a strategy of rotation of wormers throughout the year, to combat parasites more effectively.

If you suspect your horse is carrying an unacceptable parasite load in spite of your worming program, it's not that hard nor that expensive to find out for certain. You can simply scoop up a couple of his road-apples (fecal balls, for the technically-minded) into a ziplock baggie, and hand them off to your large-animal vet to be analyzed. If you happen to have a microscope handy, you can see for yourself what worm-eggs look like. Ascarids, ewwwww. But enough of them can kill your young horse

If you're not already on a regular deworming program, it's not too late to begin. Regular worming is extremely important to your equine-buddy's health and well being. Here's the thing, if you're noticing your horse's coat is a little dull and coarse, or seems especially shaggy and poor, and he's just not shedding out like he ought to; if he's got a pot-belly in spite of seeming sort of lackluster, and seems ribby and thin over his hips, withers, and neck; if he has bouts of mild colic or goes off his feed, if he seems depressed or dull in attitude; if he just doesn't seem to gain weight no matter how many groceries you're putting in front of him? He's very likely carrying a worm-load that his system just can't compensate for. (You should immediately get your pal's teeth checked by a vet, as well.)

Do be aware, by the way, that if you're just beginning a worming program with a horse that's in marginal condition and is carrying a significant parasite load, you need to watch him carefully after administering wormer. Dying parasites can release toxins, and the horse may colic or develop neurological symptoms as his system tries to handle those toxins. Large amounts of dead and dying worms must pass through the intestinal tract, and can cause a blockage, in extreme cases. If you've recently assumed care for a rescued animal, for example, this can be extremely important to monitor. Your local large-animal vet can give you even more detailed information.

I'll try not to gross you out with pictures and descriptions of the parasites your horse has (every horse has some worms—it's a natural state of being that we make worse with modern horse-husbandry practices.) Historically, the compounds we've used to combat parasites can become less effective, as the worms become increasingly resistant. We've seen this happen with both fenbendazole (Panacur or Safe-Guard) and mebendazole (another wormer in the benzimidazole family.) In the spring, you're especially interested in targeting tape-worms, as well as those parasites you need to be concerned about with every worming: strongyles, roundworms, and pinworms. If you haven't already wormed for any leftover bots, (usually done after a couple of good hard freezes) then you need to think about that, too. Now, moxidectin (marketed under the brand name Quest) kills both bot fly larvae and encysted small strongyle larvae, but is widely considered to be a wormer that you should use with extreme caution and strict attention to the dosage instructions. Many vets recommend a double-dose of one of the benzimidazole wormers, rather than moxidectin. Pyrantel pamoate (you probably know this wormer most commonly as Strongid) controls both large and small strongyles, in most of different phases of their life cycle. Since we're all about killing as many of the nasty little beasties as we can possibly kill, without causing our horses undue stress, pain, or illness, we're going to design a worming schedule that incorporates several different chemicals, to complement each other throughout the year; as well, we need a schedule that takes into account the various larval stages of the parasites we're targeting. Bots. Eww, again. These parasites have to be specifically targeted in your worming program

So the specific chemical thats going to be most effective for killing most of those specific parasite groups is ivermectin. Unfortunately, because ivermectin has become such an overwhelmingly popular horse-wormer, there's been a marked increase in incidences of tapeworms—ivermectin doesn't do anything at all to tapes, but it's the most effective thing going for most of the other parasites mentioned. So either you need to administer ivermectin earlier in the season, or at this point you need to give a wormer that combines ivermectin and praziquantel. No worries, there are several good brands on the market. The thing to be certain of, though, is that the spring parasite control schedule contains both ivermectin and praziquantel, whether administered together or separately.

Still with me? It's not as overwhelming as it seems, and unless your horse is traveling a lot, boarded in overcrowded conditions, or has constantly changing pasture-mates (all of those conditions demand extra attention and more frequent parasite-control) my worming schedule ultimately boils down to a rotation that looks something like this:

• February/March - double-dose of fenbendazole (Panacur)
• May/June - ivermectin with praziquantel (Equimax)
• July/August - double-dose of pyrantel pamoate (Strongid)
• November - ivermectin with praziquantel (Equimax)

Depending on your climate, the environment in which your horse lives, and your own vet's recommendations, you might want to make adjustments in rotation timing, dosages, and which wormers you administer. If I've been traveling with my horse more than usual and I don't know what he's likely to pick up from turnout in strange pastures, I'll usually worm more frequently, in which case the rotation looks more like this:

• February - ivermectin with praziquantel (Equimax)
• April - double-dose of fenbendazole (Panacur)
• June - double-dose of pyrantel pamoate (Strongid)
• August - ivermectin with praziquantel (Equimax)
• October - double-dose of fenbendazole (Panacur)
• December - either a double-dose of pyrantel pamoate (Strongid), or a careful single dose of moxidectin (Quest)

No matter what sort of program you and your Equine Vet devise together, you and your horse will both rest easier for having a plan and keeping to it. And you'll be much, much happier not having to poke through those road apples looking for evidence of crawly critters.