Flax seed in most reputable stables in Europe as well as in the States.

In the past the flax was fed only as a part of bran mash and never by itself as it became more fashionable lately.

The seed is too small for chewing and most of it goes undigested through the system, not to mention that it is toxic, especially when fed in larger doses.

When flax is fed not soaked and not boiled it did not have the mild laxative effect

I do not recommend the flaxseed to be fed on daily basis and un-boiled, not even in small amounts.

It is best if the flaxseed (linseed) is soaked (2-6 hours) in cold water and then boiled (simmered) 30 or more minutes in order to get all its benefits, as well as, to destroy the toxic prussic acid it contains. During boiling it absorbs a lot of water and becomes "jelly".

The most important part of the flaxseed and why it is fed is the soluble fiber, which becomes gelatinous when exposed to water (similar to psyllium). It is helpful in preventing impaction and sand colic as the fiber swells and the gel like consistency traps and suspends sand, bringing it out of the system. It is therefore the main ingredient when feeding a bran mash on regular basis of which one main reason is the prevention of colic.

Flaxseed also has high concentration of Omega 3 fatty acids, including alpha-linolenic acid. Horses need a minimum level of key fats to maintain good health. These essential fatty acids are Omega 3 and Omega 6. A horse cannot produce these fats in their body, thus they are an essential part of his diet.  

    Recommendations:
    Feed only as a part of bran mash once or twice per week, about 1/4 of a cup/2 oz. (measured dry before soaking) per horse, per feeding. See bran mash for more. Store in cool dry place. The whole seed keeps for a long time; the ground flax will go bad fairly quickly.