Test deworming program | Fecal samples will determine which horses are low shedders and can be treated less frequently
SASKATOON — Internal parasites can present risks to horses’ health, including colic, diarrhea, respiratory disease, decreased performance, rapid weight loss, loss of body condition and even death.
But many horse owners may not realize some traditional deworming practices are making parasites immune to the treatments.
Parasite resistance results from improper dosing, incorrect administration of medication and over-treatment by deworming too often or deworming horses that don’t need it.
While rotating different classes of dewormers was once thought to slow or prevent resistance, evidence shows this is not the case.
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Exposing parasites to more kinds of dewormers, more often, gives them more opportunities to develop immunity.
Resistance affects entire farms, not just individual horses. Because resistance to all classes of dewormers has been documented, horse owners are advised to rethink deworming practices before anti-parasite drugs become ineffective.
Strategies like good pasture management and intelligent use of rotational and interval deworming has proven merits.
However, veterinarians now recommend incorporating simple tests to gauge how well a deworming program is working, and avoid administering ineffective treatments that promote further resistance.
Veterinarians use a fecal egg count test (FECT) to identify the type and quantity of parasites in a horse.
Fecal samples are examined under a microscope and a horse that consistently produces samples containing more than 200 parasite eggs per gram is classified a high shedder. One that produces fewer is a low shedder.
Though only 20 percent of the horses in a herd typically harbour 80 percent of the worms, all horses have been traditionally treated the same.
Veterinarians now recommend deworming low shedders less frequently than high shedders, or sometimes not at all.
This retains a population of parasites that are not yet resistant to de-wormers and can dilute the population of resistant worms by breeding with them. Plus, treating the low shedders less often saves money.
“When first instituting fecal egg counts in your herd, each (adult) horse should be tested once in the spring and again in the fall,” said Dr. Katherine Robinson, the equine field service resident at the Western College of Veterinary Medicine in Saskatoon.
“A third test may be recommended the following spring, depending on the findings for the individual horse.”
Horses less than a year old should be monitored more frequently.
Once a horse is dewormed following a FECT, a fecal egg count reduction test, or FECRT, can be performed 14 days later to determine the efficacy of the dewormer.
An egg count reduction of 95 percent means the dewormer was effective. If the count is reduced by less than that, resistance is a concern.
To collect and prepare samples:
- Watch each horse defecate.
- Wearing latex gloves, take one or two fecal balls per horse from the top of the pile, avoiding samples that have touched the ground.
- Place each sample in its own zippered plastic bag or sealable plastic container, labelling it with the corresponding horse’s name.
- Refrigerate or transport in a cooler if samples cannot be taken to a veterinary lab within about 45 minutes after collection. Hatched eggs cannot be identified under the microscope so the results would falsely show a lower egg count for that horse.
Robinson cautions against purchasing do-it-yourself kits because of the challenges involved with handling a microscope and correctly identifying egg species.
“There is potential for much to be either missed or over-interpreted when owners do fecal egg count tests themselves, leading to inaccurate counts,” she said.
“Most veterinary labs charge be-tween $15 and $40 to run a FECT.”
Depending on herd size and test frequency, this may prove more economical than a kit that can cost up to $700. Taking samples to a lab also provides greater confidence in test results.
Ideally, the whole herd should be tested at the same time.
“It is probably more important that when horses are dewormed, the entire herd (or horses that need to be done, based on fecal egg counts) is done at once. This … will help increase the efficacy of other management practices, such as manure removal, rotation of pastures and harrowing of pastures,” said Robinson.
FECT and FECRT take the guesswork out of deworming. Tests are simple, cost-effective and can benefit animal health.
