The skin is the largest and most visible organ of the horse’s body, so it should be obvious when something is wrong.
The good news is that it is relatively easy for your vet to examine a skin problem and take a sample to establish a precise cause. The bad news is that the lesions — areas of sore, thickened or abnormal skin — can make a good horse look hideous, sometimes distressing an owner more than their animal, simply because skin problems are so noticeable, even when not painful. There is also the fear of spread — ringworm being the classic example, which can go from horse to horse and also infect people.
An itching horse can be difficult to work and even harder to live with. Itchiness can irritate a horse to the point that he loses weight, and in severe cases can even be confused with colic.
The proper word for itching is pruritus, which is the unpleasant sensation that leads a horse to bite, scratch or rub his skin. Often this is so compulsive that the horse will damage himself: the more he scratches, the more he will itch, further inflaming the skin and producing wounds and infection.
Why do they itch?
Irritation is most commonly caused by external factors, such as biting insects including midges, flies and lice. Another common external cause is reaction to environmental allergens such as pollen, barn dust and moulds, a condition somewhat similar to human allergic eczema.
Internal causes can also make a horse itch, so your vet may suggest taking blood tests to determine the cause. Some forms of liver disease can contribute to unpleasant forms of dermatitis, especially on non-pigmented skin. Internal liver disease, sometimes exacerbated by plant toxins, can produce a nasty form of sunburn and worse, resulting in hair loss and sore skin — so be aware that many different factors can create similar end results.
It makes sense to have skin lesions properly checked out early on. Lumps like melanomas and sarcoids are usually far better treated before they have a chance to grow.
For diagnosis, it helps to sample the true, active disease and not something disguised by time and multiple medications.
Most skin diseases are more identifiable in the early stages, before the effects of different lotions, potions and pills have altered the original appearance beyond all recognition.
Equine skin is surprisingly sensitive and many of the standard antiseptics and disinfectants that are readily available can do more harm than good. Once damage has occurred, hair can change colour and skin can crust over, form scabs and become generally sore as a result of either or both inflammatory or infectious responses to various problems.
The skin can only respond to disease or damage in a limited number of ways, so there can be many different explanations for itching, lumps, bumps, rashes and/or hair loss.
Pastern dermatitis is an example of a skin disease that can have multiple causes and may vary in appearance.
Skin disease on the lower limbs is not limited to mud fever. Some horses with skin irritation in these areas will be suffering from infestations of tiny mites. These chorioptic mange mites are similar to those that cause scabies in humans.
Another form of pastern inflammation is leucocytoclastic vasculitis. This condition is caused by a disorder of the body’s immune system, which attacks the skin — particularly unpigmented areas of the lower limbs. It tends to spread up the cannon region and is usually seen on the outside and back of the legs.
Sunlight seems to aggravate the condition, which is worse in summer and in horses at pasture. Steroid treatment that diminishes the damaging inflammation is required in many cases, along with some sort of sunblock — ideally protective leg wraps, or reduced exposure to the sun. Some soothing emollients may also help, but obtain a diagnosis rather than just covering it up with cream.
As a vet in practice, I now see more cases of leucocytoclastic vasculitis, perhaps due to increased sunlight as a result of global warming, so seek veterinary advice early on, if skin problems prove persistent.
Ref: Horse & Hound; 2 July 2015