Equine worms: An Australian horse owner’s guide to modern parasite management

Internal parasites are a natural part of every horse’s environment. However, with the right management, they don’t have to become a significant health concern.

Modern veterinary recommendations have moved away from routine calendar-based worming in favour of a targeted parasite management program. This approach combines Faecal Egg Counts (FECs), strategic deworming, and good pasture hygiene to ensure horses receive treatment only when it’s needed.

This evidence-based strategy not only helps protect your horse’s health but also reduces the development of anthelmintic (wormer) resistance – an increasing concern recognised by veterinarians across Australia and around the world.

Even with the best preventative care, no parasite management program can eliminate risk entirely. Horses can still develop parasitic disease despite responsible management. If you’ve taken reasonable precautions, followed your veterinarian’s recommendations, and your horse still becomes ill due to parasites, eligible veterinary treatment costs may be considered under your Petcover Equine policy, subject to your policy’s terms, conditions and acceptance of the claim.

Why are worms a concern?

Internal parasites are common in Australian horses and can affect animals of any age. While many adult horses develop some natural immunity, foals, weanlings, young horses and older horses are generally more susceptible to parasite-related disease.

A significant worm burden may contribute to:

• Weight loss or poor body condition
• Reduced performance
• Poor growth in young horses
• A dull or rough coat
• Diarrhoea
• Colic
• General lethargy

Importantly, many horses carrying worms show no obvious clinical signs, making regular monitoring an important part of preventative healthcare. According to the Merck Veterinary Manual and AAEP, horses can shed parasite eggs without displaying outward signs of illness. 

How do horses get worms?

Most horses become infected while grazing.

Adult worms living inside the horse lay eggs that are passed in manure. These eggs hatch into larvae on pasture, where they are accidentally consumed by grazing horses, continuing the parasite lifecycle.

Because Australia’s climate often supports year-round parasite survival, managing pasture contamination is just as important as administering the right worming product.

The modern approach starts with a Faecal Egg Count (FEC)

A Faecal Egg Count (FEC) is now considered the foundation of parasite management in Australian horses.

This simple laboratory test analyses a fresh manure sample to measure the number of parasite eggs your horse is shedding.

Your veterinarian can use the results to:

• Determine whether treatment is actually required.
• Identify horses contributing the greatest amount of pasture contamination.
• Monitor the effectiveness of your parasite management program.
• Reduce unnecessary use of worming products.

Not every horse sheds the same number of parasite eggs, which is why treating every horse on the same schedule is no longer considered best practice.

Why targeted treatment is better

Using wormers only when they are needed provides several important benefits:

• Helps slow the development of wormer resistance.
• Maintains the effectiveness of available treatments.
• Avoids unnecessary medication.
• Creates a parasite management program tailored to your individual horse and property.

Your veterinarian may also recommend a Faecal Egg Count Reduction Test (FECRT) to ensure the worming product you’re using remains effective, as resistance to several commonly used worming classes has already been documented in Australia.

Good paddock management makes a big difference

Even the most effective worming products cannot replace good pasture hygiene.

Simple management practices that help reduce parasite exposure include:

• Removing manure from paddocks at least two to three times per week, particularly during warmer months.
• Avoiding overstocking.
• Feeding hay in racks or feeders rather than directly on the ground.
• Quarantining and testing new horses before introducing them to the herd.
• Co-grazing with cattle or sheep where appropriate, as most equine parasites are host-specific.
• Avoiding harrowing manure unless weather conditions are suitable, as this can spread infective larvae.

Choosing the right worming product

Different wormers target different parasites.

Your veterinarian will recommend the most appropriate product based on:

• Your horse’s age
• Faecal Egg Count results
• Time of year
• Local parasite risks
• Previous treatment history

It is also essential to administer the correct dose based on your horse’s body weight, as underdosing can contribute to parasite resistance.

What if my horse doesn’t like being wormed?

Some horses readily accept oral paste, while others require a little more patience.

If your horse is reluctant:

• Introduce dosing syringes gradually during training.
• Use calm, consistent handling.
• Ensure the full dose is swallowed.
• Ask your veterinarian for advice if administration is becoming difficult.

Work with your veterinarian

Every horse and every property is different.

Factors such as your location, stocking density, grazing management, climate and the age of your horses all influence the most appropriate parasite control strategy.

Working with your veterinarian to develop a tailored parasite management plan is the most effective way to protect your horse while helping preserve the effectiveness of worming products for the future.