How To Calculate Selenium In Other Feeds & Supplements

Learn these simple facts and you will know how much and what kind of selenium you are providing to your horse. You will need to read the label of your feed to determine the type and amount or selenium that you are providing.

Fact 1: You must supplement with selenium in the Northwest. You and your horse live in an area of critical selenium deficiency. Not supplementing with selenium is dangerous.

Fact 2: Organic Selenium is safer and more effective then inorganic. In the guaranteed analysis of feed and supplements, both are referred to as “selenium”. You must look at the list of ingredients on your feed bag to tell what source the selenium is from. It is inorganic if it says sodium selenite or sodium selenite. It is organic if it says Seleno-Yeast or Seleno -Methionine.

Fact 3: A 1,000 lb horse needs 3 mg. of Organic selenium a day. If the horse is heavier or lighter increase or decrease the selenium by the appropriate percentage. This provides enough selenium for times of stress and is very safe.

How do you know how much selenium your horse is receiving?

In grains or complete feeds, selenium will be listed in parts per million (PPM). PPM is a measure of concentration just like percent. It is convenient when there is only a small amount present.

Percent is 1 part per one hundred.
PPM is 1 part per million.

The table below will allow you to figure out how much selenium you are providing. Find the concentration of selenium on your feeds’ guaranteed analysis. You must feed the amount in the right column to provide the necessary 3 mg per day.

.3 ppm feed 22 lbs
.4 ppm feed 16.5 lbs
.5 ppm feed 13.2 lbs
.6 ppm feed 11 lbs per day
.65 ppm   feed 10.2 lbs per day
.7 ppm feed 10 lbs per day
.8 ppm feed 8.25 lbs
.9 ppm feed 7.3 lbs
3 ppm feed 2.2 lbs


If you are not getting enough selenium from the feed mix, you should add selenium. Many horses will gain too much weight if you feed enough of the complete feed to provide needed vitamins and minerals. The easiest and safest way is to correct the difference is to top dress with a vitamin mineral supplement that provides organic selenium. This will allow you to provide complete vitamins and minerals even though you are not able to feed enough of the grain mix to reach optimum levels.

Last Fact: Feeding inorganic or too little selenium is better than nothing. If you are feeding less or more than 3 mg per day, your horse will still receive some benefit. You definitely want to be sure that your horse is getting at least 1 mg. per day and less than 20 mg per day.

For more information visit our other nutrition pages:

The Critical Mineral Selenium

Why Do Horses Need Selenium

Horse Guard Funds Selenium Research

Frequently Asked Questions

Nutritionist’s Blog