Why Parasite Control Is Essential for Horses
Horses are highly susceptible to internal and external parasites, and the consequences of an unmanaged parasite burden can be severe — from colic and weight loss to skin irritation, disease transmission, and even death in extreme cases. A proactive, year-round parasite control program is one of the most important things you can do for your horse's long-term health.
Internal Parasites: The Deworming Basics
Several types of internal parasites commonly affect horses. Understanding which ones you're dealing with helps you choose the right dewormer.
Common Internal Parasites in Horses
- Small strongyles (cyathostomins) — The most prevalent parasite in adult horses. They encyst in the gut wall and can cause severe colitis when they emerge en masse.
- Large strongyles (bloodworms) — Less common today due to widespread deworming, but historically the most dangerous equine parasite. They migrate through blood vessels and can cause life-threatening colic.
- Roundworms (ascarids) — Primarily a concern in foals and young horses. Heavy burdens can cause colic, respiratory issues, and poor growth.
- Tapeworms — Associated with a specific type of colic (ileocecal). Require praziquantel for effective treatment.
- Pinworms — Cause intense tail rubbing and irritation but are not dangerous to overall health.
- Bots — Larvae of the bot fly that attach to the stomach lining. Treated with ivermectin or moxidectin.
Building a Deworming Schedule
The old approach of rotating dewormers every 6–8 weeks is outdated. Modern equine veterinary guidelines recommend a targeted selective treatment (TST) approach based on fecal egg counts (FEC).
Step 1: Fecal Egg Count Testing
A fecal egg count tells you how many parasite eggs your horse is shedding. Horses are classified as:
- Low shedders (<200 eggs per gram) — Treat 1–2 times per year
- Moderate shedders (200–500 EPG) — Treat 2–3 times per year
- High shedders (>500 EPG) — Treat 3–4 times per year
Step 2: Choose the Right Dewormer
- Ivermectin — Broad-spectrum; effective against strongyles, roundworms, pinworms, and bots
- Moxidectin — Similar to ivermectin but also targets encysted small strongyles; longer residual activity
- Fenbendazole — Effective against strongyles and roundworms; a 5-day larvicidal dose targets encysted strongyles
- Pyrantel — Good for roundworms and strongyles; daily low-dose use can help prevent reinfection
- Praziquantel — The only effective treatment for tapeworms; often combined with ivermectin or moxidectin
Step 3: Seasonal Timing
- Spring (April–May): Treat after the last frost when larvae become active on pasture
- Fall (October–November): Use moxidectin or a 5-day fenbendazole course to target encysted strongyles; add praziquantel for tapeworms
- After bot fly season: Treat with ivermectin or moxidectin to eliminate bot larvae
Anthelmintic Resistance: A Growing Problem
Overuse of dewormers has led to widespread resistance, particularly in small strongyles. To slow resistance:
- Use fecal egg counts to guide treatment rather than a fixed calendar schedule
- Perform fecal egg count reduction tests (FECRT) to confirm your dewormer is still working
- Don't under-dose — always deworm based on accurate body weight
- Rotate drug classes based on resistance patterns in your area
External Parasites: Fly Control for Horses
Flies aren't just annoying — they cause stress, spread disease, create open wounds, and can transmit serious conditions like equine infectious anemia (EIA). A comprehensive fly control program combines multiple strategies.
Types of Flies That Affect Horses
- House flies and stable flies — Bite and irritate; stable flies feed on blood
- Horse flies and deer flies — Painful biters that can transmit EIA and other diseases
- Bot flies — Lay eggs on the horse's legs and coat; larvae are ingested during grooming
- Face flies — Cluster around the eyes and nose; spread eye infections including pinkeye
- Gnats (Culicoides) — Cause sweet itch (summer eczema), an allergic skin reaction
Fly Control Strategies
Topical Fly Sprays and Repellents
Apply fly spray before turnout and reapply as needed. Look for products containing permethrin, pyrethrin, or natural repellents like citronella. Wipe-on formulas work well for sensitive areas around the face.
Fly Masks and Sheets
Fly masks protect the eyes and face from face flies and gnats. Fly sheets cover the body and are especially helpful for horses sensitive to insect bites or prone to sweet itch.
Feed-Through Fly Control
Feed-through products containing diflubenzuron pass through the horse's digestive system and prevent fly larvae from developing in manure. They work best as part of a whole-farm fly management program.
Environmental Management
- Remove and compost manure frequently (at least twice weekly in summer)
- Keep stalls dry and well-bedded
- Use fly traps and sticky tape in barns
- Consider biological controls like parasitic wasps, which prey on fly pupae
Other Parasites to Watch For
- Ticks — Check horses regularly around the ears, mane, tail, and groin. Use permethrin-based sprays for prevention.
- Lice — More common in winter. Cause intense itching and hair loss. Treated with topical insecticides.
- Mites — Can cause mange, particularly in draft breeds with heavy feathering.
Work With Your Equine Vet
Every horse and every farm is different. Work with your equine veterinarian to develop a parasite control program tailored to your horses' ages, health status, geographic location, and pasture management practices. Annual or biannual fecal egg counts are the foundation of a smart, resistance-aware deworming program.
Shop Horse Health Supplies at Paw and Tail Supply
We carry a full range of equine dewormers, fly sprays, fly masks, feed-through fly control, and more to keep your horses healthy and comfortable year-round.
