The best way to deworm your horse
In the past, the idea of deworming a horse meant you rotated different worming medicines throughout the year. Common deworming ingredients include Pyrantel, Ivermectin, and Benzimidazole.
Here is a typically recommended deworming schedule:
| Jan/Feb | Pyrantel |
| March/April | Benzimidazole |
| May/June | Ivermectrin |
| July/Aug | Pyrantel |
| Sept/Oct | Benzimidazole |
| Nov/Dec | Ivermectrin |
This worming schedule has worked well for probably millions of horse owners over the years. But research is showing that some types of worms are developing immunity to what is only recently becoming understood as overuse of these ingredients. Other types of worms, such as large strongyles are often not present in well-managed herds, and using a dewormer for these is unnecessary. So what options do horse owners have?
Fecal Test
Zero Egg Count Equine Parasite Test Kit
The goal of using fecal egg counts is to understand what class of dewormer works well on your herd (immunity is not an issue) and to understand which horses are shedding the most eggs.
To start, have a fecal test done on each horse in your herd. This should be done 3 – 4 months after your last deworming. An alternative is the have the fecal test done two weeks after worming to determine if the class of dewormer you used is effective or if your herd is resistant to it. Your veterinarian can do the fecal examination to identify any worm infestations or you can purchase test kits online and mail the kit in for results.
Usually, 30% or less of horses in a herd are responsible for most of the egg shedding. By running a fecal egg count on each horse, you can identify high, medium, and low egg loads. Horses with high rates of sheddng will be wormed more often and horses with low counts may only need worming once or twice a year.
Most Common Parasites
Small strongyle populations
Jessie Evans, DVM @ Bend Equine Medical Center noted a study conducted in the Southwest United States found resistance to Ivermectin developing in some strongyle populations. More worrisome, it also found that nearly 95% of horse herds were resistant to Panacur, 53% were resistant to Anthelcide, and 40% were resistant to Strongid. If you are worming a horse with a strongyle population resistant to the class of wormers you are using, you are wasting your money.
A fecal test 2 weeks after deworming can verify the wormer used was effective. Before deworming, have a fecal test run. This gives you a base level of infestation to measure from. Treat the horses with the correct dose of one class of wormer. Then, have another fecal test run two weeks after deworming.
large strongyle populations
Treating all horses on the property with Ivermectin twice a year will eliminate any large strongyles on the property. When new horses are introduced they should immediately be dewormed with ivermectin and kept away from other horses for 4 days. the horse can then be included with the established deworming schedule on the farm.
Roundworms
Adult horses develop immunity to roundworms. But roundworm eggs can last for up to 10 years in the environment and can cause severe harm to foals. Foals should be started on a worming schedule at 6 months old and your veterinarian can suggest the best plan.
Pinworms
Does your horse rub his hind end raw? It’s possible the problem is pinworms. Adult pinworms crawl out of the horse’s anus and use a sticky substance to attach their eggs to the horse. This substance is what causes your horse to itch and itch and itch. Pyrantel pamoate is usually the best at eliminating pinworms. A repeat deworming about 2 months after the first is required to kill any eggs that have hatched and re-infested the horse.
