Autumn Worming Starts in Spring: Protecting Horses in Australia

When it comes to strongyle control, the most important battleground isn’t inside your horse — it’s on your pasture. The infective larvae living in the grass determine how many worms your horse carries. That means what happens in spring directly impacts your autumn worming outcomes.

Why Spring Sets the Scene

As temperatures rise to around 15–25°C, eggs passed in manure can develop into infective larvae in as little as five days. The full lifecycle takes approximately 5–6 weeks, including time inside the horse before new eggs are shed.

Between August–December, multiple lifecycles can occur. One egg can become an adult female worm shedding thousands of eggs per day. With each cycle, larvae accumulate on pasture, increasing exposure.

While most adult horses develop some immunity, high larval intake increases the risk of heavier burdens, including encysted larvae. These often don’t cause problems until autumn or even winter, which is why spring management is so important.

Practical Steps to Reduce Larval Build-Up

1. Use Faecal Egg Counts (FECs) Strategically

• Test all horses at the start of spring.
• Deworm only high shedders.
• Treating half your horses can reduce up to 95% of egg shedding.
• Young, high-shedding or immunocompromised horses may need repeat testing later in spring.

Blanket worming increases costs and drives resistance without improving outcomes.

2. Stay on Top of Manure

• Remove manure regularly where possible.
• Avoid overstocking.
• Rest paddocks if manure collection isn’t practical.

Reducing manure reduces larvae.

3. Consider Cross-Grazing

If possible, rotating with cattle or sheep can help “clean up” horse worm larvae, as most parasites are species-specific. The exact strategy depends on pasture size, growth rates, and stocking density.

Bottom Line

Effective autumn worming begins months earlier. By limiting pasture larval build-up in spring, you reduce worm exposure, lower the risk of encysted larvae, and improve the effectiveness of autumn treatments.

Smart parasite control isn’t about dosing more — it’s about managing pasture, testing strategically, and staying ahead of the lifecycle.