Rhabdomyolysis and Selenium levels

or... maybe better known as Tying- up or Azoturia. It's one of the things that endurance riders fear. Quite some time ago, I was informed that I might run a greater risk with Maggie being prone to tying up because of her build, (heavier muscling) and was encouraged to supplement Vitamin E, Selenium and Lysine, which has shown to help lessen tying up problems.

Not being one to just do as told, I went looking for myself before I did anything. Turns out, Maggie is not really at any greater risk than any other horse for sporadic or chronic Rhabdomyolysis. Any horse, any breed, any age can run into issues with the sporadic version if they are over worked beyond their condition level or being asked to perform in hot humid weather without sufficient electorylytes. Maggie is less likely to run into what is considered the Chronic version , which is then split into two categories; PSSM (polysaccharides Storage Myopathy) which I won't get into , or RER(Recurrent Exertional Rhabdomyolysis). According to an article written by Lydia F. Gray, DVM, MA in August 2007, it states that researchers has once believed that RER was due to the build up of lactic acid in the muscles, however recent studies are showing that it may be more related to abnormal regulation of intracellular calcium that makes muscles more sensitive to contractions. As it turns out, there are three breeds that are prone to REr, which include Standardbreds, Arabians and Thoroughbreds. Maggie doesn't fit into any of these, however she is Morgan , which did influence the standard bred... so I suppose there is always the possibility. The good news is that it really has nothing to do with muscle/body build, from what I can glean.

This whole topic did make me want to be sure that , given her recent workload in the last two months , she was receiving an adequate amount of Selenium , Vitamin E and Lysine.

I also live in an area considered Selenium deficient. That means that our hay and our grass in the pasture may not be providing enough.

I found this article. In this article, it gives some very interesting information about plants and Selenium uptake. The article also indicates that the area of Montana tends to have sufficient or higher levels of Selenium, which I found a bit surprising since that was a direct contradiction to everything I have understood for several years. I kept looking and found this resource (USGS)that gives a little more accurate information . You can zoom in and click on your county to get the exact ranges of Selenium levels. Cornell has an article which states that for areas with identified deficiencies, animals should be getting between 0.1-0.3 mg/kg per day and more specifically for horses, the nutrient requirement for simple maintenance is 0.10mg/kg per day of Selenium. According to the map (USGS) link for Flathead County, Montana, the minimum is 0.101 and the maximum is 1.926 (ppm) . If I wanted to convert that to MG/LB I would need to multiply that by 0.4536 or if I wanted to convert it to Mg/Kg I would multiply by 1.

So, roll up your sleeves and lets do some math! (not my strong suit at all) I just took the upper end ppm of 1.926 x 1 which gave me 2 MG/Kg or 1.926 x 0.4536 gives me 1 MG/LB. So, if I give nothing but hay and pasture and assuming the numbers on the USGS map are correct , it seems as though the Selenium amounts my horses are receiving are just above the recommended range for maintenance of 0.10 mg/kg thus telling me that I wouldn't necessarily need to supplement Selenium. With a hard working horse, apparently there is some wiggle room upward from those numbers as the requirements may increase with workload.

As a general rule, I have used Horse Guard for years as a broad spectrum Vitamin /Mineral supplement , along with hay and some limited pasture during the summer. Horse Guard also happens to also provider 3 mg of Selenium and 4,000 IU of Vitamin E.

But how much Selenium is too much?

According to the FDA (and ofcourse their info is always a bit suspect), a horse should not be allowed to ingest more than 3 mg per day of Selenium and they go on to say that even as small amount of 2 mg over that 3 mg , a horse can develop toxicity. When I read this, I was a bit concerned. The 3 mg that Horse Guard provides, combined with anything my horses might be getting from hay and/or pasture, (remember about 1MG/LB, I was suddenly seeing that our horses might be getting approximately 4 MG/LB per day, which was possibly creeping up into the upper ends of what was a safe number???

I consulted with my vet and she felt that while the numbers on the USGS were good general guidelines, there are variations. She was aware of several hay crops in the area that have been tested and all showed that there was definitely a deficiency. I supposed I could have my hay and soil tested but in the years I have been using the same feeding program, I have never seen any symptoms of toxicity in my horses, such as hair loss, cracked hooves, dull coat, etc. For now, I'll keep with what I know works and watch for any symptoms..

I would like to hear from anyone with any other information regarding this.