And The Vet Said..."

Selenium

At this point everyone has heard about the death of the polo ponies early this spring in Florida. The latest information available has attributed these deaths to selenium toxicity. With the majority of horses raised in selenium deficient areas, ensuring adequate selenium in the equine diet is very important. You should feel safe when using a commercially formulated product when directions are followed or under the direction of your veterinarian.

What happened in the case with the polo ponies was a mixing error on the part of a compounding pharmacy. There is an injectable supplement used in other countries called Biodyl®. This product has not been approved for use in the United States by the Food and Drug Administration. Veterinarians turn to compounding pharmacies to recreate drugs such as antibiotics, but rarely vitamin and mineral supplements because the ingredients are readily available. The pharmacy that mixed the medication found "the strength of an ingredient in the medication was incorrect". Information available at this time does not indicate if the ordering veterinarian, who was foreign and hired by the owner of the polo ponies, gave the incorrect strength to the pharmacy or the pharmacy mixed the medication incorrectly. There are many good commercially available supplements for selenium in the horse and when followed correctly are safe to use.

Selenium has many important functions and benefits in the equine diet. Some of the benefits are:

Reproductive benefits
Protection of muscle tissue
Immune system response, including resistance to viral infections
A natural antioxidant
- Fewer infections
- Better wound healing
- Better stress tolerance
- Improved ability to detoxify drugs and other chemicals
- Can assist with muscle problems

Selenium deficiencies can cause several health problems in horses, such as:

Dummy foals, problems swallowing, nursing, or moving
"Tying up"
Muscle weakness
Anorexia
Degeneration of muscles including the heart
Early embryonic death/abortions
Retained placentas

Selenium is one of the few minerals that can be accurately measured via blood or serum sample. Proper technique is very important for this lab test and should be followed closely. When horses exhibit symptoms of deficiency and lab tests confirm these findings we will often given injections of selenium, in combination with oral supplements. The injections will get selenium levels up more quickly than with oral products alone, however when sufficient levels are reached or physical improvement is obtained the oral supplements are continued to maintain these levels.

Typical selenium toxicity presents as excessive hair loss from the mane and tail, sloughing of hooves, joint erosion and lameness. The selenium level in the polo ponies was so high that it did not present in this manner. These horses died so quickly that the cause was unclear at the time of death. Only horses treated with the compound became sick and died within 3 hours of treatment. Other horses that were not treated remained healthy and normal. That is how they discovered it was the injection that was administered.

I have never seen a case of selenium toxicity in a horse from an oral supplement. I did see one case of selenium toxicity in a horse that was receiving weekly injections of selenium for an extended period of time, much longer than is recommended by the manufacturer of the product.

There are small pockets, primarily in the western states, that have soils high in selenium. I have heard of a few cases of toxicity in animals when being grazed on old pastures and given an oral selenium supplement. The old plants had absorbed high selenium levels. This is not seen in young plants that are continuously grazed or harvested for forage or even in hays that are imported to this area.

The Midwest is very deficient in selenium thus all forages and grains grown here are deficient as well. All horses should receive supplemental selenium in not only the Midwest, but the majority of the country.

Selenium is usually supplemented to horses in the inorganic form, as sodium selenite or sodium selenate. The organic form, selenium yeast, is more available to the animal as it is readily absorbed and stored in muscle tissues and has been proven to benefit animal health and performance. I highly recommend this organic form of selenium be supplemented in any older horses, horses with muscle lameness or a history of tying-up, compromised foals, horses with reproductive problems, high level performance horses or any horse that has a known selenium deficiency. This form of selenium is safe to be used in all class of horses, but it is more costly than the inorganic form that is why it is not always used in supplements.

If you have any concerns about your horse's selenium levels or supplements you may be using please contact your veterinarian or nutritionist. Please don't be concerned about supplementing this very important mineral in the equine diet. There are many more cases of deficiency of this mineral than there are toxicities. What happened with the polo ponies was a tragic error caused by humans.