The Itchy Horse

Itchy horses can be problematic in many ways. Chronic and/or severe itchiness can have a negative impact on animal welfare, particularly if it affects their rest or appetite. In addition, horses will often scratch enthusiastically on inanimate objects, damaging fencing and buildings. This rubbing can also lead to hair breakage, hair loss and even open wounds. This can lead to permanent scarring – not only unsightly, but potentially career-ending for a show pony. Finally, in extreme cases the horse can be so uncomfortable that it becomes unpredictable to handle and ride, presenting a safety issue to the people around them.

Lice

Lice are wingless insects that live and feed on warm-blooded animals. To identify lice on a horse, part the hair in multiple places over the body and neck – you’ll see the pale, oval-shaped adults moving through the follicles. Winter is the most common time for louse infestations, as thicker coats provide a perfect habitat. Treatment requires topical application of an insecticide, repeated after fourteen days. It is also advisable to remove contaminated bedding, clean stables with a disinfectant and wash rugs and grooming kits.  While lice are not inherently dangerous, their presence can indicate a suppressed immune system. Your vet may advise you to perform further investigations, such as blood tests, to rule out underling disease.                                            

Mites

Mites are distantly related to spiders and, being smaller than lice, cannot be seen with the naked eye. Of the numerous species that can infect horses, the most common is chorioptes – the feather mite. While any horse is susceptible to chorioptes, it is heavily-feathered individuals that display more severe symptoms. This involves stamping, chewing of the lower limbs or rubbing of the lower limbs on objects (e.g. water buckets). Sores can quickly develop as a result of this self-harm.  

Treatment often involves the use of an injectable parasiticide, repeated at fourteen-day intervals.

A number of topical treatments can also be used: these include pig oil and sulphur, topical flea treatments and selenium-based shampoos.

However undoubtedly the most effective adjunct to treatment is removal of the feathers, which disrupts the mite habitat and enables better contact of topical preparations. Stables, rugs and grooming kits should be thoroughly cleaned following treatment to prevent reinfection.

Pinworm

A less obvious parasitic cause of itching is the pinworm. It is a relatively large worm with a unique life cycle.

Females deposit egg packets externally around the horse’s anus and it is the sticky substance that binds the eggs that causes the irritation. The classic symptom of infection is tail-rubbing, and this will often be seen in a group of horses that are in-contact as the condition is readily transmitted between them. Diagnosis can be made by using transparent adhesive tape to sample the skin around the anus. Any eggs collected are then visualised under a microscope by your vet. Treatment can take time due to the species having a particularly slow maturation. It consists of daily washing of the peri-anal area with an appropriate parasiticide solution, application of petroleum jelly to inhibit adherence of the egg packets, and the use of specific wormers to remove adult worms. This is repeated at intervals until fresh tape strips show no more eggs.

Sweet itch    

Sweet itch is caused by an allergic response to the saliva of biting midges. As a result it is very seasonal, resolving completely over the winter months and returning again in spring and summer. The symptoms involve generalised itching, particularly at the face, neck and rump. Initially this presents as broken mane and tail hair, but over time the skin can become thickened and corrugated and hair may fail to regrow at all. Self-induced sores are common.

Unfortunately, sweet itch remains a frustrating disease to treat. The best results are seen when the horse is removed from the source of the problem – the midges. This can be done by tactically grazing the horse at times when midge numbers are low (overnight, windy days) and away from midge hot spots (ponds, trees), plus the liberal use of fly repellents & special sweet itch rugs.

Steroids can be used to control the inflammation very effectively, but there are concerns about long-term effects and it can be very expensive. Some owners report improvement when using anti-histamines, however this has not been replicated in studies. A range of commercial “sweet itch remedies” exist and generally lack any sort of clinical evidence of effectiveness. However, recently the use of in-feed nicotinamides (a form of vitamin B3) has shown some promise when introduced well in advance of the midge season. More research is required to support this. 

Atopy

Atopy is defined as the tendency to develop extreme allergic responses to harmless environmental substances (allergens). These can include pollens, feeds, dust mites, storage mites and moulds. The symptoms include itchiness affecting the whole body and the development of patchy hair loss and sores from intense rubbing.

Diagnosis of the condition is often made based on the symptoms and after excluding other common causes of itchiness. A blood test has also been developed to aid in the identification of the specific allergens a horse is reacting to. An owner can then act to limit contact with these allergens, which, as with sweet itch, is the most effective treatment. Management changes that can assist with allergen avoidance are outlined in the table below.

Allergy causeManagement change
Grasses/weeds/treesExercise on well-cut tracks, roads Remove weeds from yard Fence off trees in paddocks
Dust mitesWash rugs regularly, dry thoroughly and store in air-tight container Buy quality dust-free forage and store carefully Dust stable regularly
Storage mitesEmpty new feed bags into air-tight containers and wash containers between feed batches Rinse feed buckets daily
MouldsMaximise ventilation in stable Treat damp walls with damp inhibitor Keep rugs, tack, feed and forage dry and mould-free

If avoidance of allergens is not possible or is insufficient, steroids may be used to control the inflammation. This works best in cases where the inciting cause is temporary, for example a pollen that is present for only a few weeks, as long-term steroid use is not risk-free.

Finally, a new treatment has been designed alongside the allergy blood test, and this is known as Allergen Specific Immunotherapy. This involves increasing or decreasing the activity of the immune system to give a medical benefit. In atopy, the immune system is over-reacting to something harmless, so it is possible to desensitise the body to these allergens to avoid the resulting inflammation. This is done by injecting gradually increasing doses of the allergens under the skin over a period of weeks, to allow the body to acclimatise to them. The treatment is used widely in dogs and cats with reasonable success rates but is still fairly new to the equine market.

A horse in discomfort due to skin disease can be distressing to see and can lead to owners frantically buying all kinds of lotions and potions in an attempt to relieve the itch. However, most conditions can be easily diagnosed by your vet and an appropriate treatment plan enacted swiftly, giving a satisfying resolution for all. Even for more challenging diseases, your vet will often be able to give hints and tips on management as well as keep you up to date with new research that could result in new treatment options.  

Worming

Small Redworms (Cyathostomes)

These are the most common worms in horses and they are infected from pasture contaminated by eggs passed out in faeces of infected horses. Although these worms are more prevalent in the summer they can be present all year round.

The eggs can develop into adults in the gut within 5 weeks, they can either attach to the gut wall or be absorbed into it and reduce the ability of the gut to absorb nutrients leading to weight loss, diarrhoea and general ill thrift. These worms can also encyst into the gut wall as larvae and delay their development to adults.  Emergence of these encysted larvae can cause major gut damage leading to severe diarrhoea, weight loss, colic and even death.

The adult stages are readily detected by faecal worm egg counts (WEC) and it is sensible to worm your horse based on the results of this. The encysted larvae will not be shown up by WECs so it is important to treat for these once a year (usually in the autumn).

You can reduce pasture contamination by avoiding overgrazing/overstocking of pasture, regular poo picking and cross grazing with sheep/cattle.

Encysted Small Redworm –  Owners Leaflet

Tapeworms (Anoplocephala spp.)

These worms tend to attach to the gut walls and can interfere with gut motility and cause irritation, they are a major cause of colic (research suggests up to 20% of spasmodic colic can be attributed to tapeworms). It is spread by an intermediate host (the forage mite) and infections occur all year round. Infection can be detected via a blood or saliva test but will not be shown on a WEC. Equisal Saliva test kits are available from Milbourn Equine which you can do yourself and your vet will analyse the results and advise you.

Pinworms

Pinworms are becoming increasingly common due to their location at the end of the digestive tract as ‘newer’ wormers tend to be absorbed before they reach this point. The female lays eggs around the anus and this can lead to perineal irritation and tail rubbing. They are generally not harmful and are more of a nuisance/ irritant to the horse. The adults are readily killed with a double dose of a ‘pyrantel’ based wormer but it is important to also disinfect any area the horse has rubbed on (fences/haynets/rugs etc)as otherwise the horse can become re-infected by ingesting the eggs.

Bots

Bots are actually flies that have part of their lifecycle within the horse. Eggs are laid on the hair by a fly, they are consumed by the horse and migrate to the stomach where they attach and can cause some inflammation/ulceration before being passed out in the dung. However they are not a major health concern unless present in very large quantities.

Lungworms 

Lungworms are very rare in horses unless they are immune-compromised or are grazing alongside donkeys who are relatively commonly infected.

Large Redworms

Large redworms migrate to the blood vessels causing damage to major organs, historically they caused very serious illness but due to regular use of wormers nowadays they are less of a concern.

It is our advice to worm once yearly with a wormer containing moxidectin that kills encysted redworm larvae (ie Equest Pramox) which do not show up on worm egg counts.

In between times we recommend worm egg counts are performed and only to worm if these show a high level of adult redworms. This avoids unnecessary worming, reduces the risks of worms becoming resistant to wormers and is likely to reduce your costs!

We offer a worming programme for an annual fee which provides worm egg counts throughout the year. Please note tapeworm testing is at an additional cost.

Alternatively join our Equine Healthcare Plan, to help you save money on tapeworm testing and other additional preventative healthcare costs.