Seaweed and Kelp Supplements for Horses

Horses on beachHorse feed supplements derived from seaweed or kelp have been developed to add trace minerals, especially iodine, that may be missing in a horse's basic feed ration.

Equine Seaweed supplements contain minerals, amino acids and vitamins.

There has been a lot of debate and controversy in the equestrian world about the potential benefits to be gained from feeding equine seaweed supplements to horses - which will be discussed and reviewed here.

There is a danger that iodine toxicities occur when a horse is fed too much seaweed - but, if fed with care, kelp and seaweed can provide unique benefits to a horse's health.

In the Orkney Islands, off the mainland of Scotland, it was noticed that sheep grazing on seaweed were generally in better overall condition and had more resistance to illness, especially coughs and respiratory problems such as COPD and SPAOD. This led to the development of specialised feed additives based on sea weed and kelp.

It appears that the reason seaweed and kelp may benefit horses and ponies is in both the combination of nutrients and the content of Algin.

It is the iodine content of the seaweeds and kelp used in an equine supplement that is most important.


Iodine is a key trace element in nutrition.

It enters into the life of every cell in the body and its more decisive action is its effect upon the thyroid gland, which, through its secretion of thyroxine, controls the rate of metabolism.

There is a delicate balance to be maintained when feeding equine feed supplements containing iodine. While deficiencies of iodine in a horse's diet can cause goiter in foals, excessive levels of iodine have also been known to cause this condition

Careful studying of the label should reveal the amount of iodine in a feed supplement.

If you have any doubts about the amounts of iodine in a chosen equine kelp supplement it is safer not to add this to a horse or pony's feed.

Claimed benefits of feeding seaweed supplements to horses

  • Stimulates the thyroid.  
  • Calms nervous horses.  
  • Anti-bacterial  
  • Increases fertility in the horse.  
  • Treats iodine deficiency
  • Antibiotic  
  • Antirheumatic
  • Removes heavy metals from the body
  • Improves skin & coat condition
  • Anti-ulcer
  • Anti-inflammatory

Amino Acids to be found in Seaweed

  • Arginine
  • Alanine
  • Aspartic acid
  • Coleucine
  • Cysline
  • Glutamic acid
  • Glycine
  • Histidine
  • Lysine
  • Methionine
  • Phenylalanine
  • Proline
  • Serine
  • Threonine
  • Tryptophan
  • Tyrosine
  • Valine

History of feeding seaweed to horses

  • Varieties of seaweed have been used as nutritional additives for animals since 600 BC in China and Japan
  • Seaweed has been fed as a supplement since at least the 5th Centuryin Ireland, Scotland and Norway.
  • After World War 1 - when sources of fodder were limited - studies were made on the use of seaweed for animal food with positive results.
  • During WW2 these studies were continued in Ireland. It was concluded that seaweed was valuable as a feed additive, although not nutritious enough to be a major feed source.

Other calming herbs, vitamins and minerals

  • Valerian
  • Taurine
  • Inositol - a B vitamin
  • Thiamin
  • L Tryptophane - an amino acid
  • St John's Wort (Hypericum)
  • Chamomile (contains magnesium)
  • Zinc

Things to do before feeding seaweed or kelp to your horse or pony

  • Consider carefully why you feel you need to feed an equine seaweed supplement to your horse.
    If you can't come up with a specific reason, such as a known iodine deficiency, then it is probably best that you don't add a seaweed supplement to feed.
  • Check the iodine content of the kelp or seaweed supplement that you wish to use.
    If the supplement thatyou have selected does not list the iodine content on its list of ingredients then DO NOT FEED IT.

Amount of seaweed supplement to feed to a horse 

  • The average horse requires about 2mg of Iodine per day with toxicity occurring at 40mg/day
  • At 3 g per day you are adding approx 1.5mg of Iodine to the diet
  • If you feed your horse other equine supplements containing iodine it is essential to add these amounts in your calculations.
  • Carefully weigh the amount of seaweed or kelp supplement you feed to your horse each day.
  • NEVER allow your horse to have unlimited access to seaweed


Don't overfeed seaweed to try to quickly correct an iodine deficiency in a horse - as there is a danger of creating a damaging level of iodine toxicity.

As with all medicines and supplements carefully read the manufacturer's instructions to determine the correct dosage.

There is a particular risk if too much seaweed or kelp is added to the diet of mares in foal and lactating mares - any excess of iodine is accumulated in the placenta and in the milk - foals of mares fed on diets with a high level of iodine have a chance of developing iodine toxicity.

Foals born to mares with an excess of iodine in the placenta may be born very weak or even dead and may develop bone or skeletal abnormalities.

  Advice about the benefits of feeding seaweed an kelp supplements to a horse or pony