Encysted Redworm In Horses

Encysted small redworm (ESRW) are the hibernating larval stages of the small redworm that bury themselves in your horse’s gut wall. During the autumn and winter, when the environmental conditions are less favourable for small redworm larvae to develop on the pasture, the proportion of encysted larval stages within the horse’s gut wall gradually increases. In the spring when the weather warms up, they emerge simultaneously in considerable numbers, causing severe damage and inflammation to the gut lining which can result in the disease syndrome ‘larval cyathostominosis’.

The results of this mass emergence can cause sudden weight loss, hypoproteinaemia (low blood protein), peripheral oedema, diarrhoea, colic and even death. In horses where pasture management has been poor and worm control has been inadequate, large, encysted burdens can accumulate. 

Identifying Encysted Redworm in Horses

Saara says the symptoms of encysted small redworm are not always easy to detect, this stage can’t be picked up by a FWEC (faecal worm egg count). Badly affected horses will often look slightly bloated due to the inflammation. This can make a horse look pregnant or can give the appearance of being overweight. This can clearly be seen in free roaming equines such as the new forest pony which have not been treated so therefore have a high worm burden, although it is thought that typically, native breeds may have a stronger resistance to parasite burdens. Once clinical signs of cyathostominosis are evident, mortality can be as high as 50%, despite treatment. Saara warns that horses up to 5 years old are particularly at risk, with higher incidence in the spring.

Treatments for Encysted Redworm in Horses

Encysted redworm treatment is therefore essential to the horse’s health and should be combined with a horse worming programme which includes a wormer suitable for encysted redworm in the winter period. Saara recommends using a single treatment of Moxidectin (Equest or Equest Pramox), the latter treating for tapeworm at the same time. December or January may be considered as good strategic points for this treatment.

Saara has put together a few things to remember:

• Encysted small redworm won’t show up in a faecal worm egg count: Horses can harbour several million larvae yet show negative or low faecal egg counts.

• Treat every horse for encysted small redworm once a year: Ideally treat after the first hard frost but definitely before the spring.

• Use the right wormer: A single dose of moxidectin (Equest or Equest Pramox)

• Keep redworm under control in summer: Regular faecal worm egg counts from early March until October and treating according to the results will help keep redworm under control and reduce the risk of large hidden encysted burdens forming.

• Use faecal egg count reduction tests during the grazing season: The best way to ensure that your wormers are working properly is to perform a faecal egg count reduction test. This involves taking a FWEC immediately before and two weeks after worming to assess the level of worm eggs being shed. She can then advise you of the best treatment for your horse.

• Be rigorous with pasture management: Daily poo-picking, regular rotation and resting of fields and cross grazing with sheep or cattle will help keep pasture worm burdens under control.

If you have any concerns regarding the worming of your horse, please call us for advice.  Saara can always help with tailoring individual worming protocols.