Selenium Basics

Zephyr - photographed by Cathy DeeNZ soils are known to be deficient in selenium. It is not as clear-cut in Australia and not many people seem to be aware that their horses need supplementation and it is not routine for vets to do blood tests as it is over here.

Because of the consequences of too little or too much selenium, it is very important to pay attention to the amount you are supplementing your horse and check by doing a blood test annually. Take the opportunity, if your vet visits for whatever reason, to have him take a blood sample for this purpose.

 We bring this subject up because we have recently heard of a case where a horse was inadvertently poisoned with selenium because their owners were unaware of the cumulative effect of all the selenium in the different feeds they were giving to their pony. It is a legal requirement to state on the labels exactly how much selenium is contained in the product with a warning not to feed other feeds which also contain selenium or to add selenium to fertilizers.
PIC: Zephyr at 1 year. Having been fed a simle diet with Premium NZ Horse Minerals, XtraCal and salt since conception, he is in top condition.


Inorganic or Organic?

There are several ways to feed selenium;

  • ·         In its inorganic form, as in Selmit1 or Selmit 5 from your veterinarian, or as is found in most pre-mixed horse feeds. This inorganic form is more likely to cause toxicity if inadvertently fed in excess, as in when feeding multiple feeds, all of which contain selenium.
  • ·         Through the grass ie by putting selenium prills on the ground with fertilizer. However this can pose a real problem because you really don’t know exactly how much selenium the horse is getting via the grass and toxicity can occur very easily if commercial feeds with selenium added are also being fed.
  • ·         In its organic form – this is by far the safest way to feed selenium because the threshold for toxicity is much higher. Both Premium NZ Horse Minerals and Supreme contain organic selenium in the correct amount along with Vitamin E and all the minerals in their organic form necessary for optimal health and well being. All this for the same price as many of the selenium products out there that do not contain other minerals and vitamins.

This is another reason why we advocate the use of Plain Feeds and adding your Premium NZ Minerals (or Supreme Vit & Min)
Pre-mixed feeds, unless fed at the rate recommended on the bag, (which is quite a lot), will not supply enough selenium (or other vitamins and minerals).

Why is selenium so important?

Selenium is best known as an antioxidant, but it has other roles including iodine metabolism and thyroid function, fertility, repair of DNA and is vital for optimal immune function.
Selenium's antioxidant role is, working in conjunction with vitamin E, to prevent the formation of and damage caused by free radicals


What are the signs of selenium Deficiency?

Deficiency in selenium can cause a variety of symptoms...

  • increased susceptibility to disease due to a depressed immune system
  • decreased fertility in breeding horses
  • myopathy (muscle degeneration) leading to impaired, stiff movement and eventually impaired heart function - when the tongue muscle is affected it will cause difficulty in suckling and swallowing - when the muscles of the diaphragm are damaged it will cause respiratory distress.
    This is why selenium deficient horses are more prone to ‘tying up’

Red or brownish urine is indicative of the muscle damage.
It is particularly important for broodmares to have sufficient selenium in their diet from conception. A classic sign of selenium deficiency is white muscle disease in foals and young stock. The mare should supply selenium to the foal during pregnancy and through her milk when lactating. She therefore requires a good supply of selenium throughout her pregnancy to set the foal up for early life.

What are the signs of selenium toxicity?

Hoof Slough - selenium toxicity
Hoof Slough

  • loss of mane and tail and patches of hair, poor hair-coat quality
  • rings and cracks around the hoof wall, sometimes with pain around the coronet band. If the problem isn’t rectified the hooves will slough off! (Note rings and cracks can be due to other nutritional factors too)#
  • Secondary laminitis

*Premium Minerals minus selenium (Non-Sel) is available on request for any horses whose selenium levels are too high for whatever reason. It takes several months of no selenium supplementation for levels to drop back down to normal.

Why we don’t feed Kelp
Seals photogrpahed by Cathy Dee

Kelp is promoted as being a natural source of trace minerals. The trouble is, it is very high in iodine and contains only minute amounts of trace minerals. So it is actually has a very unbalanced mineral profile.

While it does contain a wide variety of minerals, vitamins and amino acids the concentration of most of these minerals in kelp is so low that it does not supply levels recommended for horses. Therefore it is inadequate when it comes to satisfying a horse's trace mineral requirements, except for iodine and potassium.

If you were to feed enough kelp to supply adequate trace minerals, you would then be causing iodine toxicity.

For instance, 60gms of kelp would contain 0.78 micrograms of copper This is such a small amount that it would not contribute at all to your horses daily copper requirements (for those who enjoy ‘mind-benders’there are 1000 micrograms in a milligram and a 1000 milligrams in a gram)

However 60gms of Premium NZ Horse Minerals ( and in Australia - Supreme Vit & Min ) delivers 66 whole milligrams of copper in an organic form and in the right ratio to zinc.

On the other hand 60gms of kelp supplies 260mgs of iodine. Even if you only fed 20gms that is still 86mgs!

If excess iodine is present it can directly inhibit the synthesis and release of thyroid hormones especially when selenium is deficient.

Iodine toxicity will occur at intakes of 5 mg/kg of dry matter consumed per day, which is equal to approximately 50 mg/day for a 500 kg horse.

The Merck Veterinary Manual reported iodine toxicities in mares at an intake as low as 40mgs per day