Deworming in horses: Modern strategies for long-term horse health

Deworming horses is one of the most important health measures in horse husbandry. However, whilst it used to be standard practice to deworm three to four times a year, our understanding of the matter has changed.

Today we know that intelligent parasite management involves more than just routine deworming treatments. It requires in-depth knowledge of parasites, targeted diagnostics and – most importantly – natural support for the horse’s gut during and after treatment.

This article shows you how to deworm horses correctly, avoid resistance to deworming agents (anthelmintics) and, at the same time, promote the long-term gut health of your animals.

Why modern deworming strategies are essential

Parasites such as strongyles, roundworms and tapeworms are a natural part of keeping horses. A certain level of worm infestation is normal and is usually well tolerated by healthy horses. However, problems arise in cases of severe infestation or when the wrong deworming strategies are used.

The challenge: decades of blanket deworming without diagnosis have led to a dramatic development of resistance. In a Finnish field study involving 112 foals from 18 farms, the anthelmintic pyrantel showed only a moderate reduction in egg count of 43% (FECRT) against (small) strongyles, suggesting widespread resistance (Näreaho et al., 2011, Veterinary Parasitology, PMID: 21689886).

A significantly reduced efficacy of ivermectin was observed against roundworms (Parascaris equorum). In the Finnish field study, the mean reduction in egg count following ivermectin treatment was only 52%, which also indicates widespread resistance.

The results of this study are alarming, as foals in particular are at increased risk of endoparasite infestation. If endoparasites become resistant to all available classes of active substances, horses will no longer be treatable.

At the same time, we now know that deworming affect not only the parasites but also the beneficial gut flora. After a course of deworming, the gut often needs some time to regain its balance. In the study by Walshe et al. (2019), the gut flora of horses had largely stabilised again around 14 days after the worming treatment. During this phase, the horse requires special support.

An overview of the most common parasites in horses

To ensure horses are dewormed correctly, the vet usually draws up a personalised deworming plan. To help interpret faecal findings and recommendations more effectively, the most important worm species and their potential effects are listed below:

Small strongyles (Cyathostominae): The most common and economically significant parasites. Around 40 different species live in the horse’s caecum and large intestine. Particularly dangerous: larval cyathostomiasis, in which masses of encysted larvae burst through the intestinal wall and can cause severe, life-threatening diarrhea.
Large strongyles (Strongylidae ssp.): Rare today, but extremely dangerous. The larvae migrate into the arteries of the intestine and can trigger blood clots, intestinal necrosis and fatal colic.
Roundworms (Parascaris spp.): The main problem in foals and young horses up to the age of four years. Adult worms grow up to 50 cm long and, in extreme cases, can cause intestinal obstruction. The migration of larvae through the lungs and trachea leads to coughing and developmental disorders.
Tapeworms (Anoplocephala ssp.): In Germany, 15 to 30 per cent of all farms are affected. Tapeworms are found at the junction of the small intestine and the caecum and can cause inflammation, intestinal blockages and colic.
Pinworms (Oxyuris equi): Largely harmless, but very troublesome. The characteristic symptom is intense tail rubbing due to night-time egg laying around the anus.
Stomach botflies (Gasterophilus ssp.): Larvae of the botfly, which remain in the stomach for eight to ten months and cause erosion of the gastric mucosa.

Selective vs. strategic deworming: Which is the right approach?

Deworming in horses has evolved from blanket routine treatments to targeted, diagnosis-based strategies:

Selective deworming (recommended only for adult horses aged 5 years and over): This method is based on the principle that only horses showing a consistently high shedding rate of strongyle eggs above a defined threshold receive anthelmintic treatment. (ESCCAP Guideline). Through regular faecal examinations (McMaster method), only horses with an egg count exceeding 200 EPG (eggs per gram of faeces) are treated. Horses with low egg counts remain untreated and form an important ‘refuge’ – their worms dilute the resistance genes within the population.

Procedure:

Year 1: Four faecal examinations between April and November
From Year 2: Three faecal examinations for a stable herd
Regardless of the result: An annual preventive worming treatment (usually at the end of the year)

Strategic deworming (age-dependent): Based on the ESCCAP guidelines, differentiation is made according to age.

Foals: Deworm three to four times a year (risk of roundworms!)
Yearlings to 4-year-olds: Deworm two to three times a year
Adult horses aged 5 years and over: Deworm at least twice a year (one to two months after turning out to pasture and when brought back in)

Crucial: Regardless of the deworming strategy you follow, an efficacy check should be carried out 14 days after each treatment by examining faecal samples. This is the only way to detect any resistance in good time.

The gut: the cornerstone of equine health

The horse’s gut is far more than just a digestive organ – it is the centre of the immune system. A large proportion of immune cells are located in the intestinal wall, and millions of beneficial microorganisms ensure:

Optimal digestion and nutrient absorption
Defence against pathogens
General well-being and performance

The problem following deworming: anthelmintics not only kill harmful parasites, they also temporarily impair the beneficial gut flora.

The consequences:

Digestive disorders
Reduced nutrient absorption
Temporarily weakened immune system
Increased susceptibility to infections

It takes around two weeks for the gut flora to regenerate. During this critical phase, your horse needs targeted support to quickly restore gut health and avoid complications.

Natural plant power for the horse’s digestive system: oregano and wormwood

Nature provides effective helpers to support the horse’s gut during deworming.

Oregano oil (Origanum vulgare): The essential oil of oregano, particularly the compounds carvacrol and thymol, has been known for centuries for its beneficial properties. Oregano oil has the following effects:

Antimicrobial: Supports a healthy gut environment
Digestive: Stabilises gastrointestinal function
Appetite-stimulating: Important in cases of worm-related loss of appetite
Antioxidant and anti-inflammatory

One drop of oregano essential oil contains 50 to 200 times the amount of active ingredients compared to dried herbs – a highly concentrated, natural aid.

Wormwood extract (Artemisia absinthium): Wormwood owes its common name to its long history in parasite control. The bitter compounds it contains (absinthin, with a bitterness value of around 20,000) and essential oils have the following effects:

Appetite-stimulating: Bitter compounds stimulate the production of saliva and gastric juices
Digestive aid: Stimulates the secretion of bile and pancreatic juices
Worm-unfriendly intestinal environment: Bitter compounds create conditions that are unfavourable for parasites but beneficial for gut health
Liver-protective: Supports metabolism and detoxification following worming treatments

The combination of oregano oil and wormwood extract produces synergistic effects: oregano stabilises and promotes feed intake, whilst wormwood optimises the intestinal environment and strengthens the natural defences.

EQUISOLVAN^® VERMI^PLUS: Natural support for deworming

When you deworm your horse, you not only want to eliminate the parasites, but also ensure that your horse tolerates the treatment well and recovers quickly. This is where EQUISOLVAN^® VERMI^PLUS comes in.

What is EQUISOLVAN^® VERMI^PLUS?

EQUISOLVAN^® VERMI^PLUS is a high-quality feed supplement based on natural essential oils, specially developed to support gastrointestinal function during deworming in horses.

The four key benefits of EQUISOLVAN^® VERMI^PLUS:

Stabilisation of gastrointestinal function: VERMI PLUS supports the intestinal flora before, during and after deworming. It helps to maintain digestion and nutrient absorption even under stress.
Appetite stimulation: Infected or recently dewormed horses often show a reduced appetite. The oregano oil it contains naturally stimulates the appetite and promotes feed intake – the basis for rapid recovery.
Natural, worm-unfriendly intestinal environment: The combination of wormwood
bitter compounds, clove and lemongrass oil creates an intestinal environment that promotes gut health whilst simultaneously creating conditions unfavourable to parasites.
Support during periods of stress: Every deworming treatment causes stress to the organism. EQUISOLVAN®VERMI^PLUS naturally reduces this stress on the body. Horse owners report that their animals appear more lively and recover more quickly.

Directions for use and dosage:

EQUISOLVAN^® VERMI^PLUS is administered directly into the mouth using a handy dosing device or mixed into the feed. The dosage depends on the horse’s size:

Ponies/small horses: 6 ml daily
Large horses up to 600 kg: 2 x 5 ml daily
Large horses over 600 kg: 2 x 6 ml daily

When to administer?

Preventative/course of treatment: At least 10 days, several times a year to maintain healthy gastrointestinal function
Before deworming: Start a few days beforehand to optimally prepare the gut
During deworming: Continue administration
After deworming: Continue for at least 7 days, preferably 2 weeks, to rebuild the intestinal flora

Benefits for the practice:

Extremely palatable – readily accepted by horses
Easy to use with a practical dispenser
Purely natural ingredients without medicinal substances
Suitable for all age groups (from foals to seniors)
Withdrawal period according to FN-ADMR: 48 hours

EQUISOLVAN^® VERMI^PLUS is not a substitute for a deworming treatment, but the ideal natural supplement in modern parasite management. It supports your horse where conventional deworming products cause stress.

Holistic parasite management: Practical implementation

If you want to deworm horses properly, there is more to it than just the deworming treatment itself. A holistic approach includes:

Faecal sample analysis as a basis: Have a faecal sample analysed before each deworming. This ensures you only deworm when necessary and with the correct active ingredient.
Targeted treatment: Choose the active ingredient based on the identified worm species and take into account known resistances in your region.
Effectiveness check: 14 days after treatment: Repeat the faecal sample analysis to check the success of the treatment. This is the only way to detect resistances in good time.
Natural support: Administer EQUISOLVAN® VERMI^PLUS before, during and after the worming treatment to stabilise gut health.
Pasture hygiene: Collect faeces from the pasture at least twice a week. Avoid overgrazing and rotate pastures regularly.
Quarantine for new horses: Only integrate new herd members after a negative faecal sample test.

Frequently asked questions about deworming horses

Does EQUISOLVAN^® VERMI^PLUS replace deworming?
No. EQUISOLVAN^® VERMI^PLUS is a feed supplement that supports gastrointestinal function during the deworming process. It does not replace a veterinary worming treatment.

How often should I deworm my horse?
That depends on the horse’s age. Adult horses aged 5 years and older should ideally be dewormed using the selective approach – based on faecal sample analysis. With strategic deworming, deworm at least twice a year. Foals and young horses require more frequent treatments.

How can I tell if there is resistance?
By checking efficacy 14 days after treatment. If egg excretion is not significantly reduced (by at least 90 per cent), resistance is likely to be present.

Can I feed EQUISOLVAN^® VERMI^PLUS on a long-term basis?
EQUISOLVAN^® VERMI^PLUS is designed for use as a course of treatment. Several times a year for at least 10 days at a time, as well as specifically around deworming dates.

Investing in long-term horse health

Deworming horses is much more than just a routine procedure. It forms part of a holistic approach to health management that combines sound knowledge, targeted diagnostics and natural support.

Would you like to find out more about Equisolvan and how it can benefit your horse? Please feel free to contact us!

Or are you interested in our range of products designed to promote equine health?
Click here to visit our online shop!