Worms in horses – reducing the risk

Worm management is an important part of every horse owner’s basic care routine. A major worm burden can be life threatening, potentially leading to colic, diarrhoea and other significant problems even after treatment, so it’s important to put steps in place to manage your horses worm burden throughout the year.   Follow these essential guidelines to help keep the threat of worms to a minimum.

How does a horse get worms?

Worms are present in the vast majority of horses at varying levels of infestation – in fact they are born and grow with these natural parasites, so a small worm burden is quite normal and nothing to worry about.  It is generally when the burden becomes larger that problems can occur.

Worm eggs are ingested from infected pasture and develop to maturity inside the horse. Eggs produced by the adult worm are then shed in the horse’s faeces further increasing the existing worm burden on the pasture, re-infecting the horse and potentially infecting new horses.

When worms are present in larger numbers, they can severely affect your horse’s health, resulting in poor body condition, colic and general ill health.  More seriously, they can also damage a horse’s intestines and other internal organs, often causing irreversible harm with potentially fatal consequences, so it’s important to keep your horse’s worm burden to a minimum.

Certain worms will affect the horse at various times of the year so it’s vital that your worming programme includes treatment with the right wormer (anthelmintic) at the right time of year. This can be achieved through a Targeted Worming Programme, including egg counts, pasture management, targeted treatment and support for your horse’s immune system to naturally remove them from the body.  This targeted approach is essential to help prevent resistance whilst reducing overall worm burdens:

Faecal Egg Counts

Carrying out Faecal Worm Egg Counts (FWEC) at regular intervals throughout the year will help you to assess whether your horse needs to be treated for worms.  This will involve obtaining a poo sample and sending it off to a lab for analysis. The general rule is to treat horses with a worm egg count greater than 200 eggs/g.  If your horse has a count of less than 200eggs/g, this means they won’t need any treatment but could benefit from natural immune support to help keep this burden low.  EquioPathics WRM Clear will help support your horse’s natural ability to remove worms from the body and can be used as part of a strategic worming programme alongside good pasture management.

Pasture Management

Poo-picking – A well-managed pasture is pivotal to good worm management to keep your horse’s burden to a minimum. With this in mind, one of the most important things you can do is that glorious task of ‘poo picking’ – removing droppings from your horse’s field on a regular basis. Ideally this should be done daily, but if not then at least twice a week for most effective worm prevention.

Stocking rates – Try to ensure that you are not overstocking pastures. A general rule is a maximum of two horses per hectare or 1-1.5 acres per horse and graze horses of a similar age together – young horses are more susceptible to a higher worm burden.

Field rotation – Sub-dividing grazing areas into smaller paddocks and grazing on a rotational basis gives recently grazed paddocks time to ‘rest’ and can be beneficial to reduce parasite populations from ‘over-grazing’.    Additionally, harrowing your pasture during drier weather will expose soil-borne worm larvae so that they dry out and die.

Mixed grazing – Consider grazing horses with cattle or sheep as this will help dilute the horse worm burden on your pasture. Sheep and cows are not affected by horse worms and are, therefore, great at hoovering them up, reducing the potential for them to affect your horse.

Targeted Treatment

There are several types of worms all with the potential to cause varying degrees of harm. Some of the most harmful parasites are not detected within FWEC and will therefore, need to be treated at the correct time of year:

Small Redworms (Cyathostomes):

Small redworms are the most common internal parasite in horses. The larvae hibernate becoming ‘encysted’ in the gut wall during the winter and emerge in large numbers as adults in the spring, causing severe damage to the intestines during the process.  They can cause weight loss, diarrhoea and colic with potentially fatal consequences, particularly at the time of mass emergence – treatment to target these worms should be during late autumn/winter, ideally around November.

Tapeworms (Cestodes)

Tapeworms can grow to 8cm in length and a width of 1.5cm.  They form into clusters at the junction between the small and large intestines where they can cause digestive disturbances, loss of condition, colic and fatal blockages.  Horses become infected indirectly through eating the infected forage mite found on grass and forage – ideally horses should be tested for tapeworm in the autumn, with a saliva based test (EquiSal) and treated if the result is positive.

Large Redworms (Strongyles) and Bots

Large Redworms are one of the most dangerous internal parasites.  They eat through the lining of the gut wall and travel through the blood vessels of the gut causing significant bleeding and damage.  They can cause rapid weight loss, diarrhoea and surgical colic.  Severe cases of infection can lead to death.

Bot flies lay sticky yellow eggs on the horse’s coat, which become ingested as the horse grooms itself.  Once in the mouth the eggs hatch out into larvae, which migrate to the stomach.  If left untreated bot fly larvae will cause inflammation in the mouth and throat, and ulceration in the stomach.

Both large redworms and bots can be treated at the same time as encysted small redworm with the same wormer.

Treatment Tips and Guidance

Whilst treating for worms at certain times is often essential to reduce worm burdens, the chemical wormer itself can have a toxicity impact on some horses. EquioPathics WRM Clear can help reduce the toxicity of the wormer and help lessen the potential for related health problems.

Additionally, conventional worm can create a massive kill off, which can result in harmful side effects for the horse.  Using EquioPathics WRM Clear to lessen your horse’s worm burden somewhat in advance of worming treatment can help reduce the risk of these side effects. WRM Clear can also help your horse recover nutritionally and physiologically from the effects of a worm burden, even after deworming, helping to support all round health and performance.

Got a question for our natural pet care team? You can ask in the comments below, or feel free to email us.

Article by Lisa Elliott, MSc Equine Science, Bsc Biology