Parasites can significantly impact a horse's well-being, and proper control is essential for maintaining their health. This article aims to provide horse owners with valuable insights into equine parasite management, including common parasites, prevention strategies and the growing concern of anthelmetic resistance.

Equine Parasites

Parasites are primarily spread to horses through contaminated environments and ingestion of infective stages. Most commonly, horses become infected by grazing on pastures contaminated with parasite eggs or larvae that have been shed in the manure of infected horses. These parasites develop in the environment, where they can be accidentally consumed by grazing horses.

Some parasites, like tapeworms, require an intermediate host such as mites, which horses inadvertently ingest while grazing. Foals can also acquire parasites through their mother's milk, particularly in the case of threadworms.

Additionally, horses can pick up parasites from contaminated water sources.

The spread of parasites is facilitated by poor pasture management, overcrowding and inadequate manure removal practices.

The most prevalent internal parasites in horses include:

1. Small strongyles (cyathostomins)
2. Large strongyles
3. Ascarids (roundworms)
4. Tapeworms
5. Pinworms

Each of these parasites can cause various health issues in horses, ranging from mild discomfort to severe complications. By working with your veterinarian, you can develop a management program to reduce the internal parasite burden in your herd while managing the risk of anthelmentic resistance.  

Signs of Parasite Infection

Horse owners should watch for the following signs that may indicate a parasite infection:

• Weight loss or poor body condition
• Dull coat
• Lethargy or decreased performance
• Colic or digestive issues
• Diarrhea
• Visible worms in feces
• Anemia
• Slowed growth rate in foals

It is crucial to consult with your veterinarian if you notice any of these signs in your horse. 

Prevention and Control Strategies

Effective parasite management involves a multi-faceted approach and collaboration with your veterinarian:

1. Strategic Deworming: Work with your veterinarian to develop a tailored deworming program based on your horse's individual needs and risk factors.
2. Fecal Egg Counts: Regularly perform fecal egg counts to assess parasite burden and determine the effectiveness of your deworming program.
3. Pasture Management: Implement good pasture management practices, such as regular manure removal and the avoidance of overgrazing.
4. Quarantine: Isolate new horses and perform fecal examinations. Deworm if needed before introducing them to your herd.
5. Proper Nutrition: Ensure your horse receives a balanced diet to support a healthy immune system.

The Role of Veterinarians and Horse Owners in Preventing Anthelmentic Resistance

Anthelmentic resistance is a growing concern. Historic parasite control practices have played  a significant role in this issue. Overuse or misuse of dewormers can lead to parasite resistance, potentially compromising the effectiveness of these crucial medications.

1. Targeted Deworming: Use dewormers only when necessary, based on fecal egg count results and based on veterinary recommendations.
2. Proper Dosing: Ensure accurate weight estimation and proper administration of dewormers to prevent underdosing, which can contribute to resistance. Be sure to follow your veterinarian’s dosing instructions
3. Regular Monitoring: Conduct fecal egg count reduction tests to assess the effectiveness of dewormers and detect potential resistance.

Further Reading and Resources

Internal Parasites in Horses (English) - AVMA

Common Internal Parasites of the Horse | Oklahoma State University

Deworming your horse - Veterinary Medical Centre

Gastrointestinal Parasites of Horses - Merck Veterinary Manual

Types of parasites and worms in horses

New Horse Arrival and Quarantine Procedures for Barn Managers | Animal Biosecurity

Fecal Egg Count Tests Improve Deworming Programs | USU

HORSES | Animal Health Laboratory - How to choose an equine parasitology test

Internal Parasites in Horses – Types, Symptoms, Treatment & Prevention | Mad Barn