WECs detect three of the most common worm species: large redworm, small redworm and roundworm. 

The life cycles of these species all involve eggs being passed in horse droppings so that larvae can hatch onto grass and be ingested as horses graze. 

Once in the body, small redworm larvae may develop into egg producing adults in as little as five weeks, however some larvae remain encysted in the gut wall in a dormant state for months or years. They don’t lay eggs when encysted, meaning a WEC will not detect them during this phase. The emergence of large numbers of encysted small redworms can cause serious damage, and is often fatal. 

To protect horses, either ask a vet to carry out a blood test between September and December to detect small redworm, or deworm routinely in autumn with a product that specifically targets encysted small redworm. . 

Although tapeworm eggs are passed in droppings, they are not evenly distributed, making them difficult for a WEC to detect. However, we can check for tapeworm through reliable changes in a horse’s saliva or blood. Kits are available that owners can use to collect a saliva sample and send for testing. 

Alternatively, horses can be routinely dewormed against tapeworm using a targeted product. This would be at either six or twelvemonth intervals, depending on the level of risk to the horse.

Some horses tend to carry more worms than others, even when managed in the same way. In fact, research shows that 20% of UK horses carry around 80% of worms. This puts their own health at risk, and makes them more likely to spread worms to other horses. 

It is important to carry out a WEC on every horse in a group so those with high burdens can be found and treated. A horse’s age will also affect their vulnerability to worms, with younger and older animals being at increased risk.

To reduce resistance, we need to preserve a population of worms that is vulnerable to current deworming drugs so current products remain effective for as long as possible. This involves allowing horses to maintain a small population of worms that does not harm their health, but prevents resistant worms taking over. 

WEC results will include guidance on whether the horse needs deworming or not. Always follow this professional advice. It may feel strange to know that worms are present and not use a dewormer, but this doesn’t put the horse at risk and is critical to tackle resistance.

Plenty of professional guidance is available to ensure owners have an effective worming programme in place. 

Owners can work with either: 

• An equine vet.
• A SQP (Suitably Qualified Person) who is trained and accredited to offer advice on worm control, carry out WECs and prescribe worming products if needed. 
• A specialist laboratory that provides services through online and postal channels. Many vets, SQPs and labs offer annual packages to support owners through the yearly cycle of checking for worms and treating when needed. They will use important additional information about a horse’s age, breed, background and management to help tailor advice.

A small worm population poses no health risk to the vast majority of horses. However, the urgent need to tackle resistance stems from the serious damage that worms can do in larger numbers. 

Depending on the type of worm, signs of infestation can range from weight loss, diarrhoea and colic to coughing, respiratory problems, dullness and lethargy. Unfortunately, once symptoms are apparent, the problem is often advanced and more difficult to treat. At this stage there is also a real chance of worms causing long-term damage or even fatality. This is why we must all take a preventative approach to managing worms in our horses.