May 23

Written by: Surgi-Care Center for Horses
5/23/2011 3:50 PM 

It is critical to understand the importance of controlling parasites as part of routine equine health care. There are more than 150 types of parasites that can infect the horse. The most common and well-known parasites are the large and small strongyles, ascarids, tapeworms, pinworms, and bots. Most internal parasites have a life cycle involving the egg, larva (immature worm), and adult (mature worm). The egg or larva is passed in the manure of an infected horse and develops in the environment. The horse then grazes and consumes the larva. The larva develops into an adult in the gastrointestinal tract of the horse. Then, the cycle starts again, with the adult worms producing eggs, which are passed in the feces.

Horses with internal parasites can appear relatively healthy. However, there are common signs of parasitism that suggest infestation. Signs include a dull, rough haircoat, lethargy/ depression, unthiftiness, pot belly, colic, and diarrhea.

A useful tool for determining the extent of parasite infection on a farm is fecal egg count. A fecal egg count requires 2-3 fresh manure balls from several horses on the farm and submission to a veterinary diagnostic laboratory. The laboratory examines the fecal sample under a microscope and determines the identification and quantity of parasite eggs. Unfortunately, a negative sample does not guarantee a parasite-free horse. Some types of parasites shed intermittently. In addition, larvae do not produce eggs, so a heavy burden of larvae would yield a negative parasite count. Therefore, it is best to collect fecal samples from several different horses on the farm.

Most dewormers are broad-spectrum, meaning that they are effective against several different types of parasites. It is typically best to use broad-spectrum products, unless tapeworms or encysted small strongyles are identified, in which more specific dewormers are required. There are three basic types of deworming programs. The first type, a continuous program, involves feeding a daily dewormer year-round or throughout the grazing season. The second type, an interval program, involves deworming at regular intervals of 1, 2, or 3 months, depending on the product and the management system. The final type, a strategic program, involves deworming only at certain times of the year or when fecal egg counts rise. Individually or a combination of these programs can be used to effectively minimize parasites on your farm. It is best to have your regular veterinarian help establish an appropriate deworming program based on the type, number, and ages of the horses on the farm, pasture management, and the geographic location.

In addition to dewormers, there are several steps to take on the farm to reduce and prevent parasite infestation. It is important to pick up and dispose of manure regularly. Also, it is beneficial to minimize the number of horses per acre, which minimizes pasture contamination. Do not spread manure in fields where horses graze, and mow pastures regularly to break up the manure piles. Separate the foals and weanlings from the yearlings and older horses because foals are more susceptible to some parasites. Finally, use feeders for the hay and grain as apposed to feeding on the ground.

Although no single dewormer or preventative measure will guarantee complete elimination of parasites on your farm, these steps are effective at minimizing parasite burden. Consulting your regular veterinarian and establishing an appropriate deworming schedule and effective management program for your farm will improve the health of the horses, minimize the risk of serious disease, improve feed efficiency, and reduce pasture contamination with parasite eggs and larvae.

Contact Surgi-Care Center for Horses at 813-643-7177 or email lkuebelbeck@surgi-carecenter.com with any questions regarding this topic.