Analysis of tail and mane hair could be used to identify horses that have been exposed to high levels of selenium in their diet, according to recent research.
Selenium is an essential mineral, required in small amounts to allow the body to function properly. It works as an antioxidant, especially when combined with vitamin E. It plays a role in thyroid function and in the immune system.
But you can have too much of a good thing. And excessive amounts of selenium in the diet can lead to chronic selenium toxicosis (selenosis).
Typically this is the result of grazing selenium rich pasture. Another possible source of excessive selenium is over zealous feeding of selenium-containing dietary supplements.
Typical signs of horses with chronic selenium poisoning include weight loss, hair loss (especially affecting the mane and tail), and lameness in all four limbs. The hoof may separate at the coronary band and in severe cases the hoof wall may slough off.