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.
Serum samples can be used to detect current high blood selenium levels.
Now scientists, led by Dr T. Zane Davis, at the U.S. Department of Agriculture 's Poisonous Plant Research Laboratory, in Logan, Utah, have demonstrated that mane and tail hair analysis can be used to identify previous periods of excessive selenium intake.
They analysed the mane and tail hairs of horses exposed to high levels of selenium in their diet. The pasture on which these horses had been grazed, over the previous three summer grazing periods, had a high content of seleniferous plants. The water also contained high levels of selenium.
Selenium is incorporated into the tail hair as it grows and remains more or less unchanged thereafter. So by measuring the selenium content of sequential segments of the hair, the scientists were able to demonstrate the fluctuations in selenium content over time. They identified an increase in selenium content that coincided with the turnout onto pasture and a decline in selenium concentration as the horses came off the pasture later in the year.
In one case they were able to demonstrate the pattern of fluctuating selenium concentration in the tail hair extending back for three years.
They conclude that in some cases hair samples can be used to determine Selenium exposure in horses for up to 3 years post-exposure.
For more details see:
Analysis in Horse Hair as a Means of Evaluating Selenium Toxicoses and Long-Term Exposures.
Davis TZ, Stegelmeier BL, Hall JO.
J Agric Food Chem. 2014 Jun 2.