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The Time and Place for a Selenium Injection

Selenium shots were once common practice for horses in selenium-deficient areas. A veterinarian once told my dad that it was the way to administer selenium to horses. However, as more research has been done, it has been determined that a daily selenium supplementation is much more effective and healthy for your horse, rather than a shot. Your horse is supposed to consume selenium, like all other nutrients, on a daily basis in order to keep balanced levels in their body.

Levels of Selenium in Forage

selenium black horse

If your forage contains adequate levels of selenium, your horse's nutritional needs will be met. However, many areas in the United States are selenium-deficient, such as the Pacific Northwest, most of California, the Great Lakes Region, and Eastern Seaboard, as well as much of Canada. The use of fertilizers on hay crops also decreases the amount of selenium in forage even further. Therefore, many horses need help to maintain adequate selenium levels for optimal health.

Options of Selenium Administration

  • Selenium salt blocks

    These blocks contain very low levels of selenium. If your horse consumes one ounce of salt a day (the average intake) your horse is receiving less than 10% of their selenium requirement. Companies are only able to put a small amount of selenium into the blocks because they have to ensure that if your horse eats the entire block of salt that they won't receive toxic amount of selenium. In addition, your horse's intake on salt can vary greatly depending on the environment and individual. Like people, some horses are salt hungry and consume a lot more salt than others. Weather also affects intake greatly. If it is hot, horses consume a lot of water and therefore need more salt, whereas when it is cold they drink less water and consume less salt. Selenium salt is better than nothing but not an effective way to supplement selenium.
  • Selenium injections

    The shots administer selenium which spikes blood selenium levels for a short time; however, horses urinate up to 70% of the selenium out that is injected within 72 hours. You also run the risk of your horse having a reaction to the injection.
  • Complete Feeds

    Complete feeds are formulated to provide energy as well as vitamins and minerals. However, if you aren't feeding your horse at the recommended levels, your horse's vitamin and mineral needs are not being met. Most complete feeds are formulated to be fed between 10-20 pounds a day. If you feed a scoop (approximately 3 pounds) of a complete feed that is formulated to be fed at 12 pounds a day, your horse is getting 25% of their vitamin and mineral requirements from the complete feed. Your horse will be selenium deficient.
  • Organic Selenium Supplementation

    Feeding your horses a supplement that is formulated to provide 3 mg of organic selenium per serving, like Horse Guard, is the best way to provide your horse with selenium. By providing a supplement, you ensure all your horse's trace mineral and vitamin needs are being met on a daily basis, without providing a lot of extra energy. You can then cater to the energy level to your horse's needs. As a company Horse Guard provided the first over-the-counter supplement with selenium for horses.

The time of a Selenium Shot

selenium shot horse

The only time I recommend a selenium injection is when a horse is extremely selenium-deficient. When blood selenium levels are below 50 ng selenium/mL of whole blood, your horse's selenium levels are dangerously low, and immediate action needs to be taken. I recommend a selenium injection be administered by your veterinarian and daily supplementation that provides 3 mg of organic selenium. Horse Guard vitamin-mineral supplement should be started immediately. Veterinarians often recommend a double dose of Horse Guard for three months, which helps to bring your horse's selenium status up more quickly. It is important to note, that their selenium status will not change overnight. Selenium is incorporated into red blood cells and enzymes that circulate in the blood. It must be available when new red blood and enzymes are being produced. The average lifespan of red blood cells in your horse is 120 days. It takes time for those red blood cells to be replaced with ones that are adequate in selenium. It typically takes a very deficient horse six to eight months to reach adequate blood selenium levels.  

How to Best Manage Your Horse's Selenium Levels

Give your horse Horse Guard which provides 3 mg of organic selenium. This will ensure that the nutritional gaps in your hay are being fulfilled. Horse Guard Inc. has an array of products that contain 3 mg of organic selenium per serving as well as other great benefits. Horse Guard, Mega-Dose, Trifecta, Super Weight Gain and Vitamin E & Organic Selenium all provide 3 mg of organic selenium per day. Check out our products online today. We are a small family company that truly cares about your horse's health. If you have questions, feel free to email Dr. Kelsey Nonella at

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