Internal Parasites

An internal parasite lives at least part of its life cycle inside the host. There are more than 150 types of internal parasites that can infect equine.

Symptoms Weight loss Listlessness and poor performance Dry, rough hair Poor appetite Bowel problems and colic Periodic lameness Breathing problems and coughing Anemia Foals that do not grow well and develop pot bellies

Diagnosis Only sure way is veterinary examination of both the horse and the feces Worm eggs revel what type of parasite is affecting the horse

The extent of injury from internal parasites depends on: The kind of parasite. The number of parasites involved, and The length of time the parasite lives in the host.

The general life cycle of internal parasites includes five stages: Stage 1- Eggs from the internal parasite pass out of the equine in the feces and is deposited on the pasture. Stage 2- Eggs hatch on the pasture and become infective larvae.

Stage 3- The equine ingest the larvae on the grass stem Stage 4- The immature parasites migrate through the equine’s tissues. Stage 5- The mature parasites live in the digestive tract and lay eggs.

The MOST abundant and harmful internal parasites affecting equine are: Large Stronglyes (blood worms) Small Strongyles Ascarids (large round worms) Pin Worms Bots* (external and internal)

Large Strongyles Bloodworms Most serious threat to horses’ health Migrate to the arteries, liver, gut wall Adults are bloodsuckers Blood clots may form in the arteries, resulting in blockage and death May cause damage to arteries leading to internal bleeding and death

Small Strongyle Spends entire life-cycle in the intestinal wall Cause ulcers that can cause digestive problems Not as serious as the large strongyle Not blood suckers

Ascarids, large roundworms Largest parasite to infect horses May grow to 15” long and size of a pencil Migrate to the liver and lungs Later they are coughed up, reswallowed and go to the small intestine Not bloodsuckers May rupture the wall of small intestine and cause death Young horses

Ascarids

Pinworms Travel to the large intestine Do not migrate through other tissues of the body Cause irritation in the anal region Horse may rub the rear quarters to relieve itching, resulting in hair loss from the tail

Tapeworms Difficult to diagnose, it is estimated that 40% of the horses in the U.S. are affected. Tapeworms are contracted during grazing, when the horse ingests the intermediate host, a mite found on plants. Once infected, tapeworms contribute to digestive problems, colic and malnourishment. Tapeworms are often undetected using normal fecal flotation methods

Bots are flies that lay eggs on various parts of the equine. Eggs hatch into larvae and are ingested by the equine when the equine licks the area where eggs are laid. Other eggs hatch and larvae crawl into the mouth, from the nostrils and lips where they mature in the gums and membranes of the inner lips.

When horsemen refer to bots, they usually mean the mature larvae that attach to the lining of the stomach. Bots cause stomach problems and can block the entrance to the small intestine causing the stomach to rupture.

Factors Affecting Horse’s worm load Age- foals and young horses are more susceptible Location- geographical and climatic Season- some are active only during specific seasons Travel Pasture load- more horses=more parasites Pasture Pals- other species can carry parasites to infect horses

Treatment Drugs- Anthelmintic (Dewormers) No one drug is effective against all the different parasites Worm medications can be purchased in several forms and administered in different ways Most common is a paste or gel dewormer Pellets feed daily

Classes of Dewormer Fenbendazole Oxibendazole Ivermectin Praziquantel Pyrantel Pamoate Moxidectin Similar products, have different active chemical to fight infestation of different worms Most are effective against more than 1 type of parasite

Deworming Most horses are on a deworming schedule Frequency depends on: History Travel New horses coming in? Number of horses in pasture Our horses are on a 3 month rotation Every 3 months they are wormed with a different wormer to cover all types of worms

Dewormers

Prevention Sanitation and good management practices are the basis of prevention Manure should not be spread on horse pastures Drag pastures to break up manure and expose it to sunlight Do not overstock pastures Alternate horses with cattle or sheep Feed hay and grain in bunks and feeders rather on the ground Keep the water supply clean Keep stalls clean

Summary Effects of disease and parasites are costly to horse owners Proper feeding and management help reduce loss Cleanliness and sanitation are the basis of prevention Proper exercise and grooming also help keep horses in good health

Summary Common external parasites are flies, lice, mites, ringworm and ticks Serious internal parasites are strongyles, ascarids, pinworms and bots Insecticides are used to control external parasites Good management practices are used to break the life cycle of the internal parasite A regular worming schedule should be followed to treat internal parasites