Mares, Foals and worms... what you need to know...

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Foaling time is upon us…


Foals are born free of parasites but they are extremely vulnerable as their immune system still needs to develop. Foals are often exposed to parasites within the first few days of life whilst out with the mare. They will need a careful schedule of tests and treatment to ensure their wellbeing.


In order to protect the foal when born, we must first protect the mare.


The mare should have routine worm egg counts every 8 weeks between March and September and tapeworm saliva tests every 6 months during autumn and spring. We advise also taking a small redworm (cyathostomin) blood test between September and December to indicate the risk from encysted larva. Give treatment only as the results indicate, worming only where there is a need, thus reducing the risk of increased resistance to our worming drugs.


Routine treatment of mares prior to foaling should not be necessary, provided they have been well managed in the months leading up to foaling.

In cases where the worm surveillance strategy detailed above has not been followed, the mare should be wormed proactively with Moxidectin (Equest) four weeks before her foaling due date.

When our foal is born.


Foals should be turned out onto clean pasture. Repeated use of the same nursing paddocks, year on year is a significant source of worm infections for young foals so should be avoided wherever possible. 


Maintaining good stable and pasture hygiene will help to reduce parasite infections in foals. Good stable hygiene by daily cleaning and regular disinfection of stalls, as well as avoiding fertilising pastures with horse manure should reduce the prevalence of roundworms (ascarids) and redworm (small and large strongyles) on your property.  


Although it goes against the advice above for worming adult horses, young foals do need proactive treatment to protect them from parasites.

Roundworms are very common in foals and yearlings and can lead to weight-loss, diarrhoea, small intestinal impaction and colic if severe infection are left untreated. Common signs of a high roundworm burden include poor weight gain, unthriftiness, a pot belly or rough coat. Migrating larvae also cause coughing and respiratory damage through pulmonary haemorrhaging. 

Foals should treat with a single dose of fenbendazole (Panacur) at three and five months of age, it is the recommended treatment for roundworm and foals should be treated with a single dose. If there is a history of disease on the property then this treatment should be move forward to two and four months of age. Before two months of age, the roundworm population in the foal will be comprised of fourth stage larvae and immature adults which are far less susceptible to worming treatments. As such, routine worming treatment prior to two months of age is unnecessary and possibly ineffective, and may make the worms resistant to future treatments. Other wormers, such as Ivermectin are much less effective at treating roundworms and should be avoided during the first five months of life.

It can be difficult to accurately assess the weight of a foal, if in doubt overestimate to ensure an effective amount is given. (Fenbendazole has a high safety margin, the dose needed to cause toxicity in horses is over 50 times the normal dose for deworming).


Foals born earlier in the year (February – April) should have a worm egg count performed at 7-8 months of age to assess for roundworm and redworms infections. Your vet will advise as to which worming treatment to use, if required.


We recommend routine treatment of foals and yearlings in November/December with a single dose of Moxidectin (Equest) which is the preferred wormer for the treat of redworm. Foals born later in the year (May-August) may not require a worm egg count as they will need to receive a Moxidectin treatment regardless. Moxidectin should not be used in foals less than four months of age.




If the young foal is scouring and you suspect an active parasite infection it is important to consult your vet as soon as possible. Dehydration and general deterioration can occur quickly in a young foal, time is of the essence.