Q: Do certain coat colours predispose a horse to having more sensitive skin?

A: A horse’s response to skin stimulation is theoretically the same, regardless of coat colour. Skin pigmentation (not coat colour itself) does, however, influence skin sensitivity to UV radiation.

De-pigmented skin types (pink skin), as is often seen in Appaloosa, cremello and albino horses, does not contain the photo-protective pigment melanin. Melanin helps to protect the skin from UVA and UVB rays and blue visible light present in sunlight. It operates as a shield to prevent direct UV damage to the DNA of skin cells and reduces stress on the skin.

UV-related skin disease

Horses can get two skin diseases related to UV light exposure. One is sunburn and the other, called photosensitization, looks like sunburn but is much more complicated.

Photosensitisation is related to the eating of photodynamic plan material. If a horse eats a plant containing a photodynamic agent, the agent enters the blood stream and reacts to UV light from the sun as the blood travels through blood vessels in the horse’s skin, causing the skin to be more sensitive. This typically affects white skin due to the increased UV penetration. Plants containing photodynamic agents include clover, St John’s Wort and buckwheat.

Liver conditions

Horses with liver disease are more prone to UV-induced dermatitis (skin inflammation) due to their inability to process the ‘metabolites’ of chlorophyll (found in plant material). To eliminate the risk of UV damage, UV defensive fly rugs and sunscreen can be applied, but if hepatitis (inflammation of the liver) is the cause of dermatitis, treatment of the underlying condition is the only way to resolve the skin disease.