Sweet itch in horses, also known as pruritus, describes the unpleasant sensation that leads horses to bite, scratch or rub at their skin.
Sometimes the sensation is so strong that horses will cause severe damage to themselves or their environment, while in extreme cases, horses cannot tolerate tack on their skin, let alone a rider.
Although poorly understood, pruritus is known to result from the stimulation of special nerve endings and receptors in the skin. In the horse, the three main factors inducing itchy skin are ectoparasites (such as biting insects), infections and allergies.
In most cases a severe itch is made up of a number of smaller itches. The point at which a horse responds to an itch will vary from animal to animal and is known as the pruritus threshold. Below this threshold the horse may have potentially itchy stimuli present, but not respond to them.
One example is that a horse can carry a burden of parasites such as lice, which cause damage to the skin, without showing any clinical signs. However, once the damaged skin becomes infected, this additional level of discomfort can push the horse beyond its pruritus threshold, causing it to rub or bite itself.
Sweet itch caused by midges typically appears in spring and settles down to virtually disappear during the winter. For this reason, purchasers need to be aware of the potential risk of buying a horse with no symptoms during the winter which, by mid-summer, could turn into a major sweet itch case.
Signs of sweet itch in horses
- Mild to severe itching and rubbing, usually along the mane, back and tail
- Loss of tail and mane hair
- Bald patches, which can look ugly and grey due to permanent hair loss and skin damage
- Areas of sore, open, broken skin, which tend to bleed
- In some cases, itching along the legs and under the belly
Investigation into the causes of pruritus should focus on the major trigger factors of parasites, infection and allergy, while remembering that it is common for more than one problem to be present.
Biting insects including lice, midges, black flies and horse flies can trigger cases of pruritus. The distribution of the sore areas, such as the classic rubbed mare and tail associated with sweet itch, can help identify if parasites are responsible. Topical treatments can help soothe these horses, with fly avoidance playing a huge role in reducing clinical signs.
Skin scrapings are useful in many cases, enabling the vet to check for lice and other skin parasites, such as mange mites. Skin samples can also be used to check for bacterial, yeast and fungal infections.
Allergy is probably the most frustrating type of itch to resolve. Reactions to food in the horse are rare and can be investigated by feeding a hay-only diet before re-introducing individual feed stuffs gradually to check for a reaction.
Contact allergies to bedding can be found by changing to a hypoallergenic material, such as hemp or paper, while inhaled allergens such as mould, pollen and dust are the most difficult to investigate. These usually require specialist veterinary expertise.
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Treatment of sweet itch in horses
Once the cause has been located, a treatment regime can be prescribed using a combination of medicines to treat the various different causes of the condition. It is vital that the treatment combats the cause of the pruritus, as well as offering the horse relief from the itch.
Steroids are often successfully used to combat the irritation, but unless they are accompanied by treatment for the underlying cause of the pruritus, a relapse weeks or months later is likely to be inevitable.
Steroids are not the only option available to make the horse more comfortable while further investigations into the cause of the problem are carried out. Soothing emollient shampoos, solutions and sprays can be used to great effect. Cold water hosing and ice packs applied to the irritated areas can also lead to an improvement. Witch hazel is also recognised as having a non-specific cooling effect on itchy skin.
Shampoos containing colloidal oatmeal and oils such as borage, tea tree, evening primrose and aloe vera can also have palliative effects. Sulphur is one of the oldest anti-pruritic products available and has positive benefits in relieving the itch.
Both humectant and emollient sprays are available as therapy in pruritic horses. A humectant is an oil-free product, which increases the water-absorbency of the top layer of the skin, producing subsequent soothing effects. An emollient is an oil-based solution, which coats the skin and prevents water loss. Oil sprays applied via a simple plant sprayer can also prevent the skin drying out.
Antihistamines can cause drowsiness and should be used with caution, but they remain safer than steroids and can give reasonable relief. There are currently no antihistamines specifically licensed for use in the horse, so many of those used by vets are human drugs.
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Prevention of sweet itch in horses
- A good midge repellent is essential — your vet will be able to guide you on this
- Many horses can be controlled by being moved to a hilltop field. Small midge breeding areas, such as water troughs, need to be cleaned often
- Stable your horse from about 4pm to 8am when midges are at their worst. Using insect-proof mesh on the windows and door of stables may help
- Keep your horse’s skin covered using an ear to tail rug designed to help prevent the condition
- Use strong ceiling fans in stables as midges cannot fly against a strong air current
- Carry out medicated treatment on a daily basis, otherwise the midges will start to bite which triggers the itch/scratch cycle
- Although there is no clinical research available, anecdotal evidence from owners of horses suffering from sweet itch suggests feed supplements can help
- Homeopathic remedies vary according to the symptoms: Vet Nick Thompson suggests if your horse is restless with the condition, over-sensitive to midges, flies and general irritations, and appears worse at night, Arsenicum album may be useful. If your horse has a greasy, smelly coat and does not seem to be too sensitive, but benefits from cool bathing, then try using Sulphur
- Speak to your vet for guidance on remedies and the correct dosage