Horses are born with internal parasites making parasitism one of the most, if not the most, common equine disease. Additionally, horses ingest and shed parasites throughout their lifetimes. Whether your horse is mostly confined, lightly grazed, or exposed to full-time pasture access, understanding your horse's level of parasite burden is critical in managing their overall healthcare.

Since you can't "see" inside your horse, you need to examine the parasites that come out of your horse (more specifically, the parasite eggs.) A Zero Egg Count fecal egg count (or parasite) test is a quantitative assessment and identification of how many parasite eggs a horse is shedding at the time of the test. In order words, a fecal egg count test tells you what type and how many parasites are potentially inside your horse’s digestive tract. Several factors can influence a fecal egg count test result, including:

• Age - foals and young horses are more susceptible to certain parasites
• Location - certain parasites are more common in some geographical areas or climates
• Season - some parasites are only active during particular seasons
• Travel – potentially exposes your horse to other parasite-infected horses
• Pasture Load- horses continually grazing in a given area may increase parasite exposure
• Pasture Mates - other animals can carry parasites that may infect your horse
• Stress - may compromise a horse’s immune system
• Health - horses with infections or certain metabolic diseases may be more susceptible to parasites
• Treatment - the residual effects of any recent deworming treatments.

Fecal egg count testing has become a recognized method for assessing a horse's egg shedding potential (a.k.a. parasite burden.)

In 2013, a subcommittee of the American Association of Equine Practitioners (AAEP) published an Equine Parasite Control Guideline and reviewed and updated those same guidelines in 2019. The guidelines state that "in order to determine the egg shedding potential for an individual horse, it is necessary to collect a fecal sample and perform a fecal egg count (FEC) ..."

Besides identifying the types and number of parasites that may be lurking inside your horse, fecal egg count tests can also be used for:

• Assisting in evaluating whether a dewormer is effective
• Establishing a burden/shedder classification (high, medium or low)
• Forming a baseline for future test comparisons
• Preparing individualize deworming treatment plans per horse

Fecal egg count tests are performed on a sample of your horse’s manure (the fresher, the better). For additional information on the collection, packaging, and shipping of equine fecal samples, check out Zero Egg Count’s Sample Shipping and Collection Instructions.

After a manure sample is collected and sent into the laboratory, it is measured and mixed with a solution to prepare the manure sample for examination under a microscope. The examination consists of counting the number of parasite eggs visible in the prepared sample. Fecal egg count tests primarily identify small strongyles (redworms) and ascarids (roundworms). The number of parasite eggs visible is reported on an eggs per gram basis (e.g., Small Strongyles at 200 EPG).

Eggs per gram is a standard measure for fecal egg counts, so you can compare your current findings to previous testing results. The higher the EPG count, the higher the number of parasites in your horse’s digestive system. The parasite EPG calculation is often referred to as a horse’s parasite load or worm burden.

A parasite load or worm burden can be used to classify a horse into a shedding or contaminator category. The AAEP classifies horses into three different levels of egg shedding categories – Low, Medium and, High.  

A horse with a fecal egg count result between 0 and 200 EPG is classified as a low shedder. A medium or moderate shedder has an EPG between 201 to 500, and a high shedder has an EPG of above 500. Fecal egg counts are an estimate of your horse’s parasite burden or worm load. The more fecal egg count tests performed on your horse, the more confident you can be about its shedder classification. Knowing your horse’s shedder classification helps you determine an appropriate deworming treatment protocol. A low shedding horse will typically need less deworming treatments than a medium or high shedder (see Table 1 for more information on classifications based on a horse's EPG test results.)

The most common internal parasites shed in seasonal patterns. As a result, EPG testing values increase in the Spring for horses living in the colder climates like the northern United States with EPG values peaking in the late Summer/Autumn and declining in the Winter months. While in the warmer milder climates like the southern United States, the opposite pattern occurs, with the peak occurring in the Winter months.

Two fecal egg count test cycles should be performed annually. One set of tests in the Spring and another set of tests in the Fall. Each set consists of a fecal egg count test before any deworming treatment and another fecal egg count test 14 days after your deworming treatment. The before-treatment test identifies your horse’s worm burden and shedder category. The after-treatment test helps determine the efficacy of the anthelmintic (how well your dewormer is working). Regular fecal egg count testing avoids subjecting your horse to excessive chemical treatments and delivers valuable information to you and your Veterinarian, which may impact your horse’s health.  

Easy to use mail-in fecal egg count test kits are available at https://zeroeggcount.com/products/zec-kit