Springtime brings more pasture turnout time for horses in many areas. Animals that graze on grasses, including horses, ingest parasite eggs that are found throughout the pasture environment. The actual parasite burden for any individual horse depends on its age, the number of horses on the same pasture, and the pasture’s size and quality.
Groups of flies on horse's face
The actual parasite burden for any individual horse depends on its age, the number of horses on the same pasture, and the pasture's size and quality.
© 2018 by Carien Schippers New window.
Internal parasites of horses can cause many intestinal problems, including gastrointestinal upset, diarrhea, and potentially colic.
Signs Caused by Common Parasites of Horses
The primary intestinal parasites of horses include roundworms (both large and small strongyles), tapeworms, pinworms, and stomach bots (see Table: Signs Caused by Common Parasites of Horses*). These worms can cause damage to the digestive tract and blood loss, and interfere with absorption of essential nutrients.
The greatest damage is caused by strongyles (also called redworms or bloodworms), and most parasite control programs are designed around strongyle control. Young horses typically are infested with more parasites and have more signs than older horses.
Most intestinal parasites are ingested while horses are grazing, from eggs and larvae deposited on the grass and upper layers of the soil. The tapeworm lifecycle involves small mites (specifically, orbatid mites) that feed on tapeworm eggs and thus contain tapeworm larvae. These mites live on grasses and are ingested while grazing.
Stomach bots are larvae of flies. The adult fly deposits eggs on the muzzle, legs, and chest of horses during the spring. When the eggs are licked by the horse, they hatch and are ingested by the horse. The larvae attach to the wall of the stomach and remain for a period of time (usually until the following spring). The bot pupae then pass into the feces, where they hatch as adult flies.
All horses should be on a deworming program that consists of either a periodic deworming treatment (usually by administering a paste) every 4 to 8 weeks or a daily dewormer in the feed. Pasture management and good grooming practices are also very important aspects of parasite control.
You may want to periodically submit samples of your horse’s feces to your veterinarian to check for the type and number of intestinal parasites.
Suggested Practices for Controlling Intestinal Parasites in Horses
- Mow and harrow pastures frequently. This breaks up manure piles and exposes parasite eggs to the damaging effects of air and sun.
- Periodically rotate pastures to other livestock (such as cattle or sheep) if possible.
- In multiple-horse settings, group horses by age to maximize the efficiency of your deworming program and to reduce exposure to certain parasites.
- Keep the number of horses per acre to a minimum.
- Place hay and grain off the ground by using a feeder.
- Remove yellowish bot eggs from horses’ coats quickly. A daily wipe-down with a warm, wet towel will stimulate the eggs to hatch, and the emerging larvae will dry out and die.
- Good grooming practices are necessary to remove the bot eggs, because they are firmly glued onto the hair.
- Rotate among different classes of deworming drugs (not just different brand names) to decrease resistance.
- Consult your veterinarian about an effective deworming program.
External Parasites
As outdoor animals, horses are also bothered by flies and ticks. These can cause sores and subsequent infection on the head, neck, ears, face, abdomen, and legs. Irritation from external parasites can also cause general upset, failure to grow and thrive, and decreased appetite (for example, fly “worry”).
Horses should be checked regularly for ticks or signs of fly damage. Fly control includes proper manure management and stall cleanliness. Many different insecticidal salves, lotions, sprays, and rubs are available that can be used to remove ticks and decrease insect irritation and annoyance.
Consult your veterinarian or extension service about an appropriate control program for your area and circumstances.
Press release article from - Routine Health Care of Horses By John A. Bukowski, DVM, MPH, PhD;and Susan Aiello, DVM, ELS.