What’s a “solid” deworming protocol?

Preventive Care

May 28

Short answer

Deworm all horses 1-2 times yearly and target your high shedding horses more often. If you deworm based on egg shedding in the manure, normal predicted parasite burden, and seasonal changes you are addressing pasture contamination, horse health, and targeting any encysted larvae that may be hiding from dewormer medications in your horse’s body.

1. All horses have worms (eww!) and it is important to recognize that no dewormer will eliminate all parasitic stages from a horse. Therefore, it is important to deworm all horses 1 - 2 times yearly.

2. Fecal egg counts (FEC) are how your veterinarian will determine if your horse classifies as a high shedder, a moderate shedder, or a low shedder. Fecal egg counts do NOT diagnose disease in horses. Typically horses will have a relatively consistent FEC value. It is recommended to have FECs performed 1-2 times yearly to stratify your horses in high/moderate/low categories for targeted deworming.

Fecal egg counts are determined using a small (single ball) sample of fresh (<24 hours) manure. The manure is mixed with a solution that causes worm eggs to float to the top, this fluid is examined under a microscope and the eggs per gram of manure is calculated based on counts. Horses with high fecal egg counts shed many eggs onto pastures, leading to contamination and infection of herd mates. Therefore, it is recommended to deworm these horses more often.

3. Deworming after a hard frost (in the fall) that kills bot flies will help clear your horse of stomach bots for the winter, while also killing other internal parasites. Deworming in the spring will kill any activated encysted larvae that may have been hiding in your horse’s intestinal wall over winter.

Note: A fecal egg count reduction test (FECRT) will help you and your veterinarian determine if you are using effective dewormers - this measures the difference between the initial fecal egg count, and a repeat fecal egg count 3 weeks later. If the two FECs are the same or there is only a partial reduction in egg shedding, the dewormer is not working properly.

Real-Life Example

It is early April and you run fecal egg counts on your herd of 5 horses. Everyone has a fecal egg count of less than 50 eggs per gram, except your young horse who has 600 eggs per gram. You deworm everyone with the product your veterinarian recommends. 3 weeks later you run another fecal egg count on 3 of the horses. The fecal egg counts come back as 0 eggs per gram & your veterinarian tells you the protocol has worked. You then plan to deworm your young horse again mid summer. The rest of the herd is dewormed in October, after a hard frost and when daytime temperatures are cooler (and the flies have died down).

Alternatively - if the second group of fecal egg count tests you submitted returned with results of 50 eggs per gram, 30 eggs per gram, and 300 eggs per gram (the young horse), your veterinarian may recommend a different product as the first recommended medication may no longer be working well against those parasites (resistance). This information can also be used to guide future deworming decisions and product selection.

It Depends

Parasite management varies based on:

• Region and climate - infection and survival rate of parasites can vary with temps and moisture levels
• Barn population density - more horses increase the variability of types of shedders parasite load
• Age (young horses often shed more)
• Weak immune status & dewormer resistance patterns - both can increase risk of infection
• Pasture management practices - Dragging pastures to break up manure to dry out on hot days
• Stomach bots (which cause ulcers through mechanical trauma) and encysted strongyles - important to deworm with appropriately dosed and appropriately selected anthelmintic drugs to kill these. At a minimum twice a year, in an average healthy horse.

Herbal products may be an effective part of some programs, but efficacy varies and should not completely replace evidence-based parasite control without veterinary guidance.