I have read that flaxseed (linseed) meal can generate toxins when fed to horses. Is it safe to feed?

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Q: I have read that flaxseed meal can generate toxins when fed to horses. Is it safe to feed?


A: Flaxseed contains cyanogenic glycosides, which are activated by enzymes in the seed to form cyanide. As long as the seed is intact, there is no cyanide development but when exposed to air or water the conversion to cyanide occurs. The longer the exposure, the greater the time for the reaction to occur.

This is why equine nutritionists recommended that flax be fed as soon as possible once it is ground. In times past when flax (linseed) was an integral part of many equine diets, flax was boiled to soften the hard outer shell. When dropped into boiling water, the enzyme deactivated and no cyanide was produced. On the other hand, if flax is put in cold water and brought to a boil, there will be some cyanide production. Heat and acid exposure deactivates the enzyme.

Whole flax seeds can be fed without any cyanide production because the acid in the stomach will denature the enzymes. Whole flaxseeds are chewed by the horse fairly effectively and may have some effect on keeping the digesta in the tract moving well, as the pectins in the flax form a glutinous gel. Some seeds, however, may escape digestion.

Commercially purchased ground flax will be “stabilized,” a heating process that denatures the enzyme, so they are considered safe to serve as-is. The stabilized product can be refrigerated after opening to extend the shelf life.

Even though there can be cyanide production when soaking or grinding flaxseeds, the total amounts are not very high. In fact, plant breeders have been working on developing lower glycidic strains of the plant during recent years. As it stands now, a horse would have to eat more than a couple pounds of raw ground flax that had been standing around awhile (or soaked in cold water) to ingest the amount of cyanide to approach having toxic effects. Normal intakes are anywhere from 2 to 8 oz per day and do not come anywhere near the amount that would be considered dangerous.

Please note that flax meal and ground flax are not the same thing. Flax meal is the product left after the oil is extracted from the seed. Ground flax is the whole seed that has been ground so that it has the same fat content as the whole seed.