Every time we change clocks around here Dr. Lacher starts to go on and on about checking fecal egg counts on our patients. It always makes me wonder what happens when they clean my litter box but Dr. Lacher told me she doesn’t work on cats, only snuggles with us. I did get her to answer about fecal eggs counts on horses and thought I would blog about it this week so here goes:
Around the early 1980s a revolution happened in equine parasite control: Ivermectin. With the use of this drug, horse owners could easily and safely remove parasites from their horses on a regular basis. Doses of up to ten times normal would not cause problems and since it was a new class of drug parasites were annihilated. Horse owners were happy, horses were happy, drug companies were happy and veterinarians were happy they no longer had to tube deworm.
We traveled along in our little universe until the late 1990s thinking everything was great and fine. Worms were a thing of the past and we should keep our horses healthy by deworming every 6-8 weeks. Sure resistance could be a problem but we just rotated products and that was that.
And we were wrong, very, very wrong.
Dewormers all have what is known as an egg reappearance period. This is the time it takes to begin seeing parasite eggs in a fecal egg count after administering a product. For Ivermectin this is 6-8 weeks, fenbendazole and pyrantel 4-6 weeks and moxidectin 10-12 weeks. You should never administer a dewormer sooner than its egg reappearance period and ideally it should be at least double that time frame. So by using Ivermectin too often we were killing off any and all sensitive parasites and only allowing the ones resistant to treatment to survive. We were creating super worms!
Most of us do not have these super worms on our properties and can avoid their creation through intelligent deworming using fecal egg counts. And here is where we get back to changing your clock and checking a fecal. Turns out in Florida we kill off a tremendous amount of the parasite load during our very hot summers. Parasite eggs cannot survive prolonged temperatures over 85 degrees. Once temperatures have decreased below 85 degrees for about 7-10 days in a row we have the potential to drastically increase our horse’s exposure to viable parasites! This means that if we check a fecal now and determine our horse’s parasite burden we can ensure they are treated effectively through our prime parasite season. By checking their burden again in the spring we can maximize the effects of a final deworming before warm temperatures decrease the need for drugs. This allows us to deworm only the horses that need it when they need it with the drug they need.
The next way we minimize resistance among the wee beasites is by keeping a low worm burden in our horses. “Whoa!” you say my horse is not going to have any worms!! Our horses were designed to have a low parasite burden and do just fine as long as the numbers don’t get too high. In fact recent research has shown low levels of intestinal parasites to be important in combating diseases of the immune system. More importantly for this topic, by keeping a small amount of worms around we ensure that resistant and non-resistant parasites breed, creating offspring who are susceptible to our deworming drugs. So again, fecal egg counts help us identify only those horses with very high burdens and target only them for therapy. This reduces the number of parasites exposed to drugs unnecessarily. This is known as refugia for those scientific types who enjoy spending time on Wikipedia.
Fecal egg counts also allow us to check for resistance to drug classes. When performing counts we always recommend a recheck fecal on any high shedders 10-12 days after dewormer administration. This allows us to make sure there was a significant drop in egg counts. If there isn’t, we know resistant parasites are a problem and we can take steps to address this very serious issue.
Deworming has definitely gone from a one schedule fits all to a customized program for you, your horse and your property. The Doctors and Technicians at Springhill Equine have been great about answering my questions while I supervise from the counter and I’m sure they would answer yours as well!
That’s all from the countertop this week. May your litter box be clean and your food bowl full!!
