Ask SAM: Excess selenium in feed impacts equine health

This column is provided by Larimer County Extension's Small Acreage Management (SAM) Program to assist rural residents.

Dear SAM,

My neighbor recently lost a horse due to selenium poisoning. Should I be worried about my horse's health?

Sally

Dear Sally,

I'm sorry to hear about your neighbor's loss. Chronic selenium poisoning does occur in Larimer County, but careful management can prevent problems. Horses rarely die from selenium poisoning unless they are euthanized because of severe lameness due to the loss of their hooves.

Selenium is an essential nutrient in the horse's diet. Too much or too little selenium, however, can cause health problems.

One of the first visible signs of chronic selenium toxicity is hair breaking off from the mane or tail giving the appearance of a bobbed tail or roached mane.

More severe toxicity results in horizontal ridges forming on the hoof wall. These ridges, or rings, can crack, causing severe lameness and hoof loss. Consult with a veterinarian if you observe these symptoms.

Selenium poisoning is most likely to occur when horses consume large quantities of forage grown on selenium-rich soils. Alkaline soils derived from shale, common along the foothills of Larimer County, are most likely to have high selenium concentrations.

There are two methods for evaluating your risk. The surest way to determine the selenium concentration in your feed is to send a grass or hay sample to a forage testing lab for selenium analysis. Forage concentrations should be below 5 ppm selenium.

You can also look for selenium indicator plants in your pasture. Woody aster, Prince's plume and several milkvetch (Astragalus spp.) species require high selenium soils to grow. If you find these plants in or around your pasture, manage with the assumption your grass is high in selenium.

Other plants, such as four-wing saltbush and gumweed, do not require high selenium soils but will accumulate selenium if it is available. These plants are not indicators of high selenium, but they should be avoided as forage plants.

If you determine your soils are high in selenium, you don't need to sell the place and move. Several management strategies can protect your horse's health. Have your hay tested to ensure you are not feeding selenium in addition to what the animals are ingesting while grazing. Feeding low-selenium, good-quality hay as a supplement to grazing will reduce the selenium concentration in the diet.

Selenium poisoning can also be managed by maintaining adequate sulfur in a horse's diet. Alfalfa hay contains more sulfur than grass and can be fed to reduce or prevent selenium toxicity. It is also important to feed a balanced mineral mix containing sulfur and copper to counter the effects of excess selenium in the horse's diet.

To learn more about small acreage topics such as weed control, pasture management, planting grass or buying a tractor attend the Small Acreage Management Workshop at The Ranch on Saturday, Sept. 15. Preregistration is $15 and limited to 40 participants. Contact Larimer County Extension at 498-6000 for more information.

SAM

Have a question about rural living? Write to Ask SAM, Larimer County Cooperative Extension, 1525 Blue Spruce Drive, Fort Collins, CO 80524 or e-mail emarx@larimer.org.