Nickel

Tiny worms, BIG  problems!

Worms are not new, but the threat they pose to our horses is increasing.

Redwings’ teams sadly deal with the immediate and long-term effects of severe worm burdens in many of our rescued horses. We have seen an increase in worm-related issues in recent years, and it is likely that a significant factor is growing resistance of worms to the drugs we rely on to control them.

Reliance on frequent, routine deworming in the past has contributed to the evolution of worm populations that are ‘resistant’, meaning they can survive the deworming process. There is now evidence of some level of resistance in all species of worms, and to all deworming products (also known as anthelmintics). 

Not only is resistance to existing drugs escalating, there are no new classes of drugs on the horizon to provide us with alternatives. We all have a part to play in slowing worm resistance and prolonging the viability of current products so they are as effective as possible when we need them to be.

Worm egg count

How can we reduce worm resistance?

We need to take a targeted approach to worming by using regular Worm Egg Counts (WEC) to tell us if and when a horse needs treatment. A fresh dropping sample allows a trained person to check the number and type of worm eggs and this is a good indicator of the overall worm population(s) present in the horse. The owner can then be given specific guidance on whether or not a deworming drug is needed.

One study found WECs reduced the need for worming by 82%. If worming is needed, the WEC also identifies which species we are dealing with so we can use the most effective product.

Few or no eggs in droppings often means worming is unnecessary. 

Working together to tackle worms

Redwings is part of a new pan-industry group, the first of its kind worldwide, which has been formed to tackle the increasing threat that wormer resistance poses to horse health and the equine industry. Controlling ANTiparasitic resistance in Equines Responsibly (CANTER) brings together voluntary representation from the widest reaches of the sector. These include leading experts in the field across prescribers, diagnostic providers, pharmaceutical companies, trade organisations, technical experts, horse owners, charities, and policy makers. 

After several stakeholder engagement events to discuss the present problem of antiparasitic resistance with representatives from across the equine industry, CANTER was formed. The group recognises that this issue has critical health, welfare and husbandry consequences and coordinated action is essential to maintain future antiparasitic efficacy and slow the development and spread of antiparasitic resistance.

The CANTER core steering group comprises of approximately 20 representatives from across the equine sector with an active interest in the sustainable control of parasites in horses. 

wec
Worm Egg Counts (WEC)

FAQ's about WECs

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.

Make a worming action plan

1. Clear muck at least twice a week, more often for youngsters!
Removing muck breaks the worm lifecycle. Worm larvae can wander for several metres, so store muck off the ground or well away from grazing.

2. Find your ideal partner
Speak to your vet about packages they may offer, see if you have any local SQPs and look online for laboratories who specialise in worm control programmes.

3. Work together
Horses on shared yards will benefit from a co-ordinated worming plan so they are tested at the same time. This can also help save money by sharing costs.

4. Plan ahead
WEC strategies will need you to take steps at key points through the year so add reminders to your calendar to help you stay on top of worm control.

5. Perfect your sampling
Choose fresh dung from a specific horse. Wearing gloves, take a pinch from four or five different parts of the dropping to put in your container. Label clearly and send samples the same day if you can, or store in a fridge overnight.

6. Go with the guidance
Always follow the advice provided with your test result. 

7. Weigh before worming
Don’t forget to weigh your horse if you need to deworm them. Round up rather than down, so if your weigh tape reads 380kg, use a 400kg dose.

8. Target tapeworm
A saliva or blood test can be carried out in spring and/or autumn to check for tapeworm. 

9. Protect your pasture
Don’t overstock paddocks and rest grazing routinely for several months if possible. Inter-grazing with species such as sheep or cows is beneficial. 

Poo picking
Perfect your sampling

Protecting young horses

All horses need protecting from worms, but those that are young, old or have compromised health are most vulnerable to developing and being affected by a large worm burden. 

Roundworms are far more common in horses under five years of age. Most healthy adult horses develop an immunity, meaning roundworm infestation in mature equines is rare. 

Young horses are also more susceptible to both large and small redworm infestation. 
However, immunity to worms can wane in older horses, meaning they are also at increased risk. 

To protect young horses from worms, work with your vet, SQP or specialist lab as soon as you know a mare is pregnant, as her worm burden will affect the foal. Foals need a specific deworming programme for their first two years while they are most vulnerable to worm damage. 

Avoid keeping young horses on pasture that is overstocked or overgrazed, and be even more vigilant about poo-picking, clearing pasture completely at least every other day.

Dory

Meet Dory

Breed: Cob
Height: 11.2hh
Age: 2 years

Yearling Dory was one of a group of ponies rescued with several welfare issues, including high worm burdens.

When Dory developed diarrhoea, worms were suspected as a possible underlying cause and he was brought into Redwings’ veterinary hospital and given intravenous fluids while more tests were carried out.

The next day Dory developed painful colic and live redworms were now visible in his droppings, confirming that encysted redworms were emerging in large numbers from his gut wall (known as ‘cyathostomiasis’). Ultrasound examination also showed that part of his intestine called the caecum had folded into itself, a catastrophic complication invariably linked to worm damage. Dory underwent major surgery later the same day to remove half of his caecum.

Only around 50% of horses survive cyathostomiasis and major surgery reduced Dory’s chances even further. Thankfully, with round the clock care, and two plasma transfusions he recovered well. Today Dory enjoys sanctuary life while being monitored and managed through Redwings’ targeted worming programme.

Dory has since been rehomed to a family that provides the protection from worms he needs.

Other worms 

Worming programmes target the most common worms, but there are other species that can affect horses. These include: 

Pinworm 
Speak to your vet if you notice your horse has a very itchy bottom.

Bots 
Bot eggs are laid on the horse’s body, usually the lower legs, and can be removed carefully with a bot knife. Bots are unpleasant, but only damaging in large numbers.

Lungworm 
There is only a potential risk to horses that share grazing with donkeys, but very small numbers of donkeys (4%) in the UK are estimated to be infected with lungworm.

Liverfluke 
Lives mainly in sheep and cows and is only passed to horses through shared grazing. Clinical disease is rare, but may be more common as milder wetter weather increases.

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