Equine Parasite Control in Australia — A Complete Guide
Parasite control is one of the most important — and most rapidly evolving — areas of equine health management. The old approach of rotating anthelmintics every 6–8 weeks regardless of the horse's actual parasite burden is now known to be counterproductive: it accelerates the development of anthelmintic resistance without necessarily providing better parasite control. Modern, evidence-based parasite management is guided by faecal egg counts and targeted at the individual horse.
This guide, written by Dr. Louise Cosgrove of EEVS – Exclusively Equine Veterinary Services, explains the current best-practice approach to equine parasite control in Australia.
The Most Important Parasites in Australian Horses
Small Strongyles (Cyathostomins)
Critical — Most CommonThe most prevalent and clinically significant parasites in adult horses. Encysted larvae can cause severe larval cyathostominosis. Resistance to benzimidazoles is widespread in Australia. Only moxidectin has reliable efficacy against encysted stages.
Tapeworms (Anoplocephala perfoliata)
High RiskAssociated with spasmodic colic and ileocaecal intussusception. Not detected by standard FEC — require a specific tapeworm ELISA blood test or saliva test. Treatment requires praziquantel (double-dose pyrantel is less reliable).
Ascarids (Parascaris equorum)
High Risk in FoalsPrimarily affect foals and horses under 2 years. Can cause respiratory signs ("summer colds"), colic, and intestinal impaction. Ivermectin resistance is well-documented — fenbendazole or pyrantel are preferred for young horses.
Bots (Gasterophilus spp.)
ModerateBot fly larvae attach to the stomach lining and can cause gastric irritation. Yellow eggs are visible on the horse's legs and belly in summer. Treatment with ivermectin or moxidectin in late autumn (after fly season) is effective.
Pinworms (Oxyuris equi)
ModerateCause intense perianal itching and tail rubbing. Not reliably detected by FEC — diagnosis is by sticky tape test of the perianal area. Treatment with ivermectin or moxidectin is usually effective.
Large Strongyles (Strongylus vulgaris)
Lower (but serious)Less common now due to widespread ivermectin use, but cause serious arterial damage (verminous arteritis) and colic. Ivermectin and moxidectin are effective. Their return is a concern if resistance develops.
Understanding Anthelmintic Resistance
Anthelmintic resistance is the ability of parasites to survive treatment with a drug that would normally kill them. It is a major and growing problem in Australian horse populations. Resistance to benzimidazoles (oxfendazole, fenbendazole) is now widespread in small strongyles across Australia. Resistance to pyrantel is also common. Ivermectin resistance is emerging, particularly in ascarids in young horses.
The Targeted Selective Treatment (TST) Approach
The current gold standard for equine parasite control is the Targeted Selective Treatment (TST) approach, which involves treating only those horses that need it, based on faecal egg count results. Research consistently shows that in any herd, approximately 20% of horses shed 80% of the eggs on pasture. By identifying and targeting these "high shedders," you can dramatically reduce pasture contamination and anthelmintic use while slowing the development of resistance.
| FEC Result (epg) | Shedder Category | Treatment Frequency | Action |
|---|---|---|---|
| 0–200 epg | Low shedder | 1–2 times per year | Strategic autumn + boticide treatment only |
| 200–500 epg | Moderate shedder | 2–3 times per year | Treat + recheck FEC in 3 months |
| >500 epg | High shedder | 3–4 times per year | Treat immediately + FECRT to check efficacy |
The Strategic Autumn Treatment — Why It Matters
The most important treatment in any Australian horse's parasite control calendar is the strategic autumn treatment, typically given in March–May. This treatment uses moxidectin (with or without praziquantel for tapeworms) and targets encysted small strongyle larvae that have accumulated in the gut wall over the grazing season. These encysted larvae are not detected by FEC and are not killed by most other anthelmintics. If left untreated, they can emerge en masse in late winter/spring and cause severe larval cyathostominosis — a potentially life-threatening condition.
Pasture Management — The Forgotten Tool
No anthelmintic program can compensate for poor pasture management. Parasite larvae develop on pasture from eggs shed in manure, and horses are infected when they graze. The most effective pasture management strategies include: removing manure from paddocks at least twice weekly (larvae develop within 3–7 days in warm, moist conditions); harrowing paddocks in hot, dry weather to expose larvae to desiccation; resting paddocks for 3–6 months; and cross-grazing with cattle or sheep, which are not susceptible to equine parasites and will ingest and destroy equine larvae.