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Overview of Parasite Control Guidance for Foals and Young Horses

Sometimes you might need that wormer!

Parasite infection and with it, wormer resistance, is now well documented as one of the biggest threats to horse health. Young horses are exceptionally vulnerable to dying from parasite related disease or suffering lifelong consequences as a result.

Advice is ever evolving as we seek a balance between the long game of wormer efficacy and the health and wellbeing of the herd or individual in front of us. 

No more so is this the case than with foals and young horses, and especially where multiple horses under five are kept together. Their predisposition to parasites, driven by their undeveloped immune systems make them particularly prone to parasitic infection.

We’ve all heard about wormer resistance and the need to minimise treatments to preserve their efficacy. And hopefully we’re doing all we can to work towards this goal. This doesn’t mean we should be frightened of treating horses that need it, or that parasite control is a hands-off threat we can do little about.

It’s time to up our vigilance for both broodmares and their offspring with a regular schedule of worm egg counts, tapeworm tests and larval culturing so that treatments can be targeted to the right species. Where treatment is needed, ensuring we follow up with reduction tests to check wormer efficacy and monitor for any resistance. Alongside this our aim should be to employ the best management practices possible, to break the lifecycle of worms on the pasture and prevent infection, rather than relying on treatments.

These are our top tips for dealing with parasite infection in youngsters:

  • Parasite control of young horses is a complex subject, and infection pressure can vary widely depending on management, stocking density and even the time of year foals are born. Seek the help of a trusted prescriber (vet, SQP or pharmacist) to put a plan in place.
  • Start early, don’t wait! The lifecycle of parasites is short. Foals are recommended their first worming treatments from 8 weeks old. From this time forward they need an age specific approach combining treatments and testing dependent on their environment, risk assessment and the time of year.
  • Monitor weight and growth regularly. Under dosing makes treatments less effective and speeds up the development of wormer resistance. Parasite infection could be a contributing factor to youngsters who aren’t thriving, use the appropriate tests to determine the right treatment. Consult your vet if signs of disease are present.
  • Avoid re-using the same paddock year on year for new foals if you can. Poo pick, rest fields and cross-graze with sheep or cattle to lower infection potential on the pasture.
  • Carry out regular worm egg count reduction tests to determine whether treatments have been effective for small redworm and ascarid and monitor resistance to the worming chemicals you are using.
  • It is now recommended to carry out regular Faecal Flotation Tapeworm Test tests for young horses, in addition to any serum antibody tests such as the EquiSal saliva or blood tests, so that reduction tests can also be used to monitor resistance to tapeworm treatments.
  • Proactive treatments for foals under six months old and seasonal treatments for the possibility of encysted small redworm are recommended for most horses under five.
  • Although the prevalence of large redworm (is currently low in the UK, youngstock may be particularly at risk due to their higher susceptibility. Monitoring for these parasites by larval culturing should be considered.

More specific guidance on managing parasite control by age, risk assessment and time of year can be found via the page links below:

For support to put a test-led plan in place for your youngstock please get in touch.

Updated Summer 2026 following release of CANTER Guidelines Chapter 11