Equine tapeworms are internal parasites that infect the gastrointestinal tract and can cause colic, diarrhea, weight loss and poor performance.

Horses become infected by ingesting these flatworms while grazing. Once inside the horse’s digestive system, the tapeworms attach themselves to the intestinal lining, resulting in inflammation and an immune response.

Tapeworms are a unique parasite, as many common deworming medications are ineffective against them, and their eggs are rarely detected in the horse’s feces. This makes diagnosis and treatment of equine tapeworms difficult. [2]

Effective parasite control is key to protecting your horse’s health. Regular deworming and fecal testing can reduce the risk of parasite infestations in horses. [3]

What are Equine Tapeworms?

Parasites are organisms that live in or on the horse and rely on the horse for sustenance while often causing harm or disease. These include internal parasites such as roundworms, tapeworms, and bots, as well as external parasites such as ticks and lice. [1]

Equine tapeworms are parasitic flatworms that infest the intestines of many mammals, including horses, donkeys and other equids.

There are three species of tapeworms found in horses: [4][5][9]

  • Anoplocephala perfoliata: The most common type of tapeworm in North American horses, has a flat body with four suckers on its head for attaching to the intestinal wall; mature tapeworms measure between 2 to 8 cm (0.8 to 3.1 in) in length and 1 cm (0.4 in) in width
  • Anoplocephaloides mamillana: A relatively rare type, with mature worms measuring around 5 cm (2 in) in length and 5 mm (0.2 in) in width
  • Anoplocephala magna: Notably longer than the other types, with mature worms reaching lengths of up to 80 cm (31 in) and widths of 2.5 cm (1 in)

Despite their differences in size, all three species produce irregularly shaped eggs with a similar structure.

All species of tapeworms pose a significant health risks to horses. Following best management practices and veterinary deworming guidelines is essential to prevent infestations and related complications.

Symptoms

Tapeworm infections in horses are often asymptomatic, meaning the horse may not show any noticeable signs of infection. In some populations, up to 80% of horses may carry A. perfoliata in their intestines without ever displaying symptoms. [2][6][5][3]

When horses do show symptoms of a tapeworm infestation, they may exhibit signs such as: [2]

  • Colic
  • Weight loss
  • Diarrhea
  • Poor coat condition
  • Lethargy
  • Poor performance

Symptoms vary in severity depending on the extent of the infestation and any concurrent health issues.

Risk Factors

Tapeworms are easily transmitted from the environment to horses, so all equines are at some risk of infection. It’s generally assumed that horses have some internal parasites, including tapeworms, at any given time.

Particular risk factors for tapeworm infection include: [2][3][5]

  • Age: Younger horses have less developed immune systems, making them more susceptible to parasitic infections than older horses.
  • Time of Year: The highest intensity of tapeworm infection occurs in late summer and fall.
  • Access to Pasture: Grazing on pasture exposes horses to oribatid mites, which serve as intermediate hosts for tapeworms.

Unlike other equine parasites, maintaining good pasture hygiene may not reduce mite prevalence.

Surprisingly, having more pasture area per horse increases the risk of tapeworm infection, possibly because large pastures with ample vegetation benefit mite populations. [5]

Conversely, horses kept on the same pasture year-round and relying on hay supplementation may be less likely to ingest mites and tapeworms. [5]

Transmission

Understanding the equine tapeworm life cycle is critical for horse owners to effectively manage parasites, reduce transmission risks, monitor horse health, and implement preventative measures. [2]

The tapeworm life cycle comprises five stages: [2][3][4][7][8]

  1. Egg shedding: The life cycle begins when adult tapeworms residing in the horse’s intestines produce eggs. These eggs pass out of the horse’s body through the feces into the environment.
  2. Intermediate host ingestion: The tapeworm eggs are ingested by oribatid mites, which are small arthropods commonly found in soil, hay, and grass. These mites act as intermediate hosts, harboring the juvenile parasites while they mature.
  3. Larval development: The tapeworm eggs hatch within the mite’s body, and the larvae develop into a specialized stage called