Deworming. Every horse owner has done it, but there is often confusion surrounding when to do it, how often to do it, and what product to use. SmartPak has heard some of the most common myths surrounding this common practice and offers the following advice to help clear the air and demystify deworming.

“Many horse owners have been deworming their horses the same way for a long time, based on recommendations from years ago that no longer apply,” said Lydia Gray, DVM, MA, SmartPak’s Staff Veterinarian and Medical Director. “By taking a more modern approach to parasite control that is based on the latest science, we can do a better job of protecting our horses from damage due to internal parasites.”

Myth: Rotating dewormers prevents resistance and is still the best way to protect against parasites.

Of the three chemical classes that horse owners were advised 30 to 40 years ago to rotate between, parasites have become widely resistant to one of them (benzimidazoles), somewhat resistant to another (pyrantel), and are showing emerging resistance to the third (macrocyclic lactones like ivermectin and moxidectin). When horse owners give a benzimidazole like fenbendazole or oxibendazole, few, if any, worms might be killed. The best way to protect your horse is by only using dewormers that are effective against parasites.

Myth: Targeted deworming is a ton of work (and expensive!).

The fact is, targeted deworming is actually less work and less expensive … and it’s more effective! If a horse’s fecal comes back less than about 200 eggs per gram of feces, then the horse is likely a low egg-shedder and only needs to be dewormed twice a year. If the results show more than 500 eggs per gram, then the horse is likely a high egg-shedder and needs to be dewormed more often, maybe four to six times during the grazing season in your area. Consult your veterinarian to schedule fecal egg counts and determine the best deworming program for your horse.

Myth: A horse doesn’t need to be dewormed because the fecal always comes back negative.

It’s critical to realize that a negative fecal egg count test does not mean a horse is parasite-free. Believe it or not, there is little correlation between fecal egg count results and a horse’s parasite load. A horse with a negative fecal still almost assuredly has intestinal parasites—those parasites simply are not actively shedding eggs. Failing to deworm based on a negative fecal could have serious health consequences. The American Association of Equine Practitioners recommends that even horses with a negative fecal, or those categorized as low shedders, be dewormed once or twice annually.

Myth: Horses that never leave the barn don’t need to be dewormed.

While horses do technically get “infected” with parasites, it doesn’t happen exactly like getting infected with a contagious disease like influenza or rhinopneumonitis (equine herpesvirus). With parasites, a horse can reinfect himself with his own intestinal worms (yuck!). So even if you have just one horse that never goes off-site, he could still have quite a parasite load just from the eggs he himself passes and reingests.

Myth: Horses should be dewormed regularly year-round.

An expert in parasitology once compared deworming horses to mowing your lawn. In the North, you wouldn’t mow your lawn in January, as the grass doesn’t grow then. And in the South, you wouldn’t cut grass in August because, again, it’s probably not actively growing then. So, if you’re in a more northern climate, you might be able to refrain from giving dewormers when parasites aren’t active.

“There are factors such as geographic location and your horse’s parasite egg shedding status, just to name a few, that should be considered when developing a parasite control plan,” added Gray. “It’s important to remember to work alongside your local veterinarian, as they know the area and your horse’s health best.”