Tail-rubbing: is it pinworms? Or something else?

The most common symptom people report to me when getting a FEC is “rubbing their tail”. However, contrary to popular belief, tail-rubbing is not a symptom of strongyle or other worm-infections, except for pinworms. If a horse is rubbing their tail in response to a pinworm infection, diagnosis of pinworms should be based on the presence of pinworm eggs on the skin around the anus – it’s a thick, yellowy-white paste that is easily seen and identified by owners (see image below).  Pinworms may also be passed in the manure, as they live close to the end of the colon and within the rectum. If worms die, or horses are stressed and pass lots of watery manure, the worms can be easily flushed out. The presence of worms in the manure in small amounts (5 – 10) is no real cause of concern. Pinworms can be easily distinguished from other worms by their size (females are 5 - 8cm with long tails, males about 1cm long).  

Examples of pinworm eggs around horses' anus. Left: a low burden, probably does not require immediate treatment. Right: an example of a higher pinworm burden indicated by more eggs. This is likely to require treatment

If there are pinworm eggs, what should you do? Overall, pinworms in smaller burdens, cause very little problems and so to prevent overuse and development of drug resistance, pinworms can actually be left alone until the time comes to treat for strongyles. If there is a vast amount of eggs around their anus, indicating a large burden and the horse is rubbing their tail enough to cause injury, a single treatment with a dewormer will be enough to remove the worms. There is anecdotal evidence of pinworms becoming resistant to the mectin dewormers (moxidectin, abamectin, ivermectin) so the best option will be to use oxfendazole or an oxfendale+abamectin combination.

Female pinworms in manure (left) and isolated. Note their long elongated tails. These are not present on Ascarids (which are generally >10cm long)

If a horse is rubbing their tail and there are no pinworm eggs, then it is highly likely that the tail-rubbing is a sign of another condition.

So if it’s not worms, what could it be? Firstly, check the condition of their skin and coat. Poor skin condition may lead to itchiness, and this is the most likely reason your horse may be tail-rubbing. Adding in supplements to their diet to improve skin and coat health may be all that is needed. Protein, fats and B vitamins can make a difference. B vitamins are required for building the proteins that are required for good skin and hair growth, so it is worth having a look over their diet and making sure nothing is lacking.

If tail-rubbing is more serious, it may be a skin infection. These can range from bacterial or fungal infections through to ectoparasites. I can’t write to bacterial/fungal infections – these would need veterinary diagnosis. However initial treatment can be medicated shampoos to see if it elevates any symptoms.

The most common ectoparasite that would cause itching are horse lice. These are be identified by seeing the adult lice living on the hairs/skin. Treatment is with washing horses using an insecticide (pyrethroid) shampoo/wash. However this needs to be repeated several times as the eggs are tough and not highly susceptible to insecticides.

Less common, but more serious, is infection with horse mites. Serious mite infection will lead to mange. Mites should be treated with washes containing appropriate drugs, or oral ivermectin/moxidectin treatment. (Hence why some people with itchy horses think it was worms that caused the itchiness, as using an ivermectin dewormer decreased symptoms.)

If your horse is tail rubbing, first, check for pinworm eggs. If there are none, consider their skin condition, and if there is anything you can do to help improve it.