Parasite Control

For years, the standard practice for parasite control in horses was routine deworming with a rotation of the product used.

This is no longer the case. Today, due to serious concerns about resistance to the limited products available, veterinarians recommend routine fecal egg counts (FEC) instead to allow for targeted deworming.

In any herd of horses, there are generally a few animals who are considered “high shedders” – they routinely are more susceptible to the parasites and carry a higher worm load. Since they are home to more parasites, they also shed the eggs more, and can easily spread the issue to other horses if not more carefully managed. Other horses, however, have excellent resistance to parasites and do not need frequent deworming.

To determine which horses actually require treatment, a FEC is performed. Spring is the best time, but summer and early fall work as well. Don’t try to do a FEC in the winter, as many of the parasites will become encysted and don’t shed any eggs during the winter months. To have a FEC done on your horse, simply collect a fresh fecal sample – 2 or 3 balls will do – and put it in a plastic bag labelled with your horse’s name, age, date of collection and date/product of previous deworming. Keep the sample cool in a fridge or cooler and deliver it to your veterinarian within the day so they can get the most accurate count possible. Give your clinic a call before you collect the sample, as some clinics may have certain days they accept samples for FEC.

Horses who show less than 200 eggs per gram (epg) on FEC are considered low shedders and do not need to be dewormed at this time. Horses with 200-500 epg on FEC are moderate shedders and should be dewormed. Any horse with a FEC over 500 epg is a high shedder and should be dewormed, and rechecked in two weeks to ensure the product used was effective. If the product you’re using is effective (ie – you recheck your high shedders 2 weeks post deworming and they now show no ova seen on FEC) then DO NOT rotate dewormers. Introducing another product just gives the parasites in your herd the chance to become resistant to it. If you have a product that works, continue to use it. If, in the future, you did end up with resistant parasites, you’d then be able to switch to another product that those parasites have not been exposed to for many generations.

All horses should be dewormed once annually in early winter, once everything is good and frozen, because not all parasites are detectable on FEC and an annual deworming is good insurance.

As I’ve been doing FECs at work for the past year, I decided it was probably worthwhile to get the equipment here at home to be able to monitor my own herd. Our results pretty typical of any average herd – for example, of our 17 horses, on this round of FECs we had 3 moderate shedders and 2 high shedders who need deworming, and the rest of the herd had little to no parasite activity and don’t need to be dewormed right now. In a couple months, when the freeze has settled in and killed parasites in their environment, we’ll do a blanket deworming of everyone.

Worth mentioning is that of the horses that do need deworming, 2 of them are the 2 chubbiest horses on the place – if you wait to treat for parasites until your horse is showing symptoms, they have a very serious health risk.

Discuss with your equine veterinarian what products they recommend for your area/herd. Remember that if you’re dealing with Miniature Horses, Quest isn’t a recommended dewormer as it’s very difficult to safely dose for small and young animals.

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