Question

I've been told I live in a selenium-deficient area of the country. How can I tell if my horse is actually deficient in selenium?

Answer

The easiest way to tell if your horse is selenium deficient is with a blood test. To assess selenium status of a horse, concentrations can be measured in serum, plasma, or whole blood. You can coordinate with your local vet to have a sample taken and sent off for testing. Whole blood selenium levels are indicative of chronic levels of selenium intake, while serum and plasma levels are indicative of short term intake of selenium. The bigger question, if you’re located in a selenium-deficient area, is whether or not your forage is providing enough selenium, and if not, is your fortified feed making up for the difference.
You can have your forage tested by sending a sample to a lab such as Equi-Analytical. The forage source most important to evaluate is the one that provides the majority of your horse’s forage intake. If your horse is maintained on pasture and that is the primary source of forage, follow the lab directions on collecting samples of grazed areas of the pasture. Alternatively, if local-grown hay provides the bulk of your horse’s forage intake, its selenium concentration will be more influential. Make sure you take a representative sample by collecting portions of hay from not just one bale but from different bales found in the load. The best method of obtaining samples is through the use of a specially designed tool, or forage sampler, that can core a bale. These instruments can be expensive, so if you don’t have access to one, just do the best you can to get a representative sample. Your local extension agent might be able to help you with forage sampling and testing.

Once you know the nutritional composition of your horse’s forage, total daily selenium intake can be determined by multiplying the selenium concentration in the forage by the daily intake of forage and combining that with the amount supplied by your horse’s feed. Comparing this to the recommended daily intake for your horse will will let you know whether its requirements are being met or not. Then, you can formulate a plan to combat selenium deficiency, or prevent it from occurring.

Contact a qualified equine nutritionist for help if you encounter problems.