Why You Should NOT Rotate Horse Dewormers
Deworming your horse is crucial, but it turns out we've been doing it wrong.
Horse deworming isn't optional. It's crucial.
Why does your horse need it? Because all horses are at risk for parasite infection, even those that rarely leave home. As a conscientious horse owner, you probably have always made sure to rotate medications in order to protect your horse from these nasty parasites. You probably give your horse Ivermectin and Strongid on a rotational basis every 2-3 months, thinking this is a really great regimen.
Bad news! In recent years, veterinarians have been seeing more and more resistance to these medications: They are just not as effective as they used to be. Rotation is no longer considered a guarantee against infection. And over-use is thought to be a main contributor to resistance.
The American Association of Equine Practitioners puts it bluntly:
Why does your horse need it? Because all horses are at risk for parasite infection, even those that rarely leave home. As a conscientious horse owner, you probably have always made sure to rotate medications in order to protect your horse from these nasty parasites. You probably give your horse Ivermectin and Strongid on a rotational basis every 2-3 months, thinking this is a really great regimen.
Bad news! In recent years, veterinarians have been seeing more and more resistance to these medications: They are just not as effective as they used to be. Rotation is no longer considered a guarantee against infection. And over-use is thought to be a main contributor to resistance.
The American Association of Equine Practitioners puts it bluntly:
Discontinue deworming all horses
with fixed intervals year-round (e.g., every 2 months), and stop blindly rotating anthelmintic classes.
with fixed intervals year-round (e.g., every 2 months), and stop blindly rotating anthelmintic classes.
Here are the complete current American Association of Equine Practitioner recommendations for deworming horses:
Why Do Vets Now Tell Us To Stop Rotating Dewormers?
The problem is that we are giving Ivermectin or Strongid to horses that aren't infected, and giving them too often. This is the same problem doctors are worried about with respect to antibiotics. We've unwittingly bred some super-bugs by over-using antibiotics!
So just as physicians now are writing prescriptions for antibiotics only when they are absolutely necessary, veterinarians recommend using these parasite medications more sparingly.
This means most horse owners have to forget everything they thought they knew about this aspect of horse care. Instead, we need to adopt new regimens to keep our horses healthy.
Here is an excellent brief video in which Dr. Janice Posnikoff demonstrates how to deworm even the finickiest horses.
- Perform fecal egg count reduction tests (FECRT) annually to ensure that you are using effective dewormers in every herd or barn. (This is a test where your horse’s manure is examined to check for parasite eggs.)
- Recognize that no anthelmintic will eliminate all parasitic stages from a horse.
- Continue using fecal egg counts (FEC) once or twice a year to stratify horses into low, medium, and high shedders to reduce pasture contamination.
- Deworm all horses at a baseline rate (once or twice a year) and target selected horses more often based on FEC (strongyle high shedders).
- Do not use FEC to diagnose disease in horses; there is no correlation between FEC and disease-causing parasite life stages.
- Discontinue deworming all horses with fixed intervals year-round (e.g., every 2 months), and stop blindly rotating anthelmintic classes.
Why Do Vets Now Tell Us To Stop Rotating Dewormers?
The problem is that we are giving Ivermectin or Strongid to horses that aren't infected, and giving them too often. This is the same problem doctors are worried about with respect to antibiotics. We've unwittingly bred some super-bugs by over-using antibiotics!
So just as physicians now are writing prescriptions for antibiotics only when they are absolutely necessary, veterinarians recommend using these parasite medications more sparingly.
This means most horse owners have to forget everything they thought they knew about this aspect of horse care. Instead, we need to adopt new regimens to keep our horses healthy.
Here is an excellent brief video in which Dr. Janice Posnikoff demonstrates how to deworm even the finickiest horses.
Happy riding!
As long as you’re here, check these out!
Equestrian Products That Make Your Riding and Horse Care Easier and Better!
What to Feed A Horse
Six Vital Horse Facts That Every Horse Owner Absolutely Must Know
Common Horse Ailments and How to Treat Them
Copyright Denise Cummins, PhD March 3, 2016; Updated May 31, 2024
The Thinking Equestrian
