By Dr. Danielle Willenborg
“It’s spring, that means I deworm my horse, right? Maybe not!”
Intestinal parasites are something that horse owners have been concerned about for years. Many believe that they should deworm adult horses at least twice a year, once being in the spring of the year. That may not be the case anymore, and if you are deworming when it is not needed then you may be causing more harm than good.
The most common intestinal parasites we worry about as veterinarians are: large strongyles, small strongyles, and bots. The two most concerning in the springtime are the strongyles. Large and small strongyle larvae are picked up off the grass when horses are grazing, they are ingested and travel through the gut where they then reproduce and eggs are then shed into the environment through feces. Once eggs are shed they form into larvae where the life cycle then starts again.
There are other parasites such as round worms, tapeworms, lungworms, hairworms, stomach worms, and threadworms but these are not as common and therefore not as much a concern at this time.
Determining if you have a parasite problem is the first step, which you can do by bringing a fresh fecal sample to your veterinarian. We will then perform a test called a fecal flotation to look for parasite eggs.
If it is found that you in fact have a parasite problem, we will recommend a de-wormer based on the number of eggs and type of worms seen. We may also make recommendations about pasture decontamination ad deworming of other pasture mates or barn mates. In this way, we are able to treat the specific problem in a direct way, without guessing as to whether there is a problem or not.
If it is found that horses do not have a large parasite problem and you deworm anyway, then you may be aiding in parasite drug resistance. Resistant worm populations are not affected by the deworming drugs that are commonly used. This happens when we deworm when the problem is not severe or use the same medication over and over again year after year. If resistance continues to rise, one day our medications may no longer be useful with no new deworming medications on the horizon. This would then leave us with a large number of ill horses without much to do to help. This is why it is important to contact your veterinarian and bring in a fecal sample before you decide to deworm your adult horses this year. Help us to fight drug resistance by turning to us before you head to the store to buy that de-wormer.