Dear Ask the Vet,
I have been feeding my horse a product called Reitsport 100 HA. It contains a large amount of flaxseed. I have read that flaxseed has been linked to thyroid problems, cushings disease, lethargy or behavior problems and infertility in horses. Is this true? If it is true, is it a certain type or quality of flaxseed that produces these results. Thank you, LK, Texas
Every so often I receive a question like yours about the safety of flax seed, so I would like to reassure you and everyone else that feeding flax seed to horses is safe and should not be cause for concern. To my knowledge, flax seed has not been linked to the problems you list above. On the contrary, research suggests the anti-inflammatory properties of the omega-3 fatty acids contained in flax seed may be helpful in certain medical conditions such as these. For example, omega-3 fatty acids may help prevent laminitis, a major problem in older horses with Cushing’s disease. Also, omega-3 fatty acids may improve the fertility of stallions with certain quality issues.
The next issue is what form of flax seed should be given to horses. You probably know people who grind it, others who soak it, and still others who boil it. The reason people process flax seed in one of these ways is to release the omega-3 fatty acids and other helpful components. It appears that if whole flax seeds are fed, they simply pass through the digestive tract into the manure and do not provide any benefit to the horse. Therefore the hard outer hull must either be crushed or softened to release the omega-3 fatty acids. Unfortunately, releasing the helpful components of flax seed also releases harmful components (cyanogenic glycosides and enzymes), which is why some people boil flax seed, to dissipate this precursor to cyanide. However, a recent study confirmed that stomach acid inactivates the enzymes that interact with the cyanogenic glycosides to form cyanide so that is why toxicity is not observed. To read more on this study please visit the Canadian Journal of Veterinary Research.
By the way, you may hear flax seed or flax seed oil referred to as linseed or linseed oil. Although they are the same thing, if you use linseed oil make sure it is cold-pressed feed-grade and not the solvent-extracted wood finish. On a final note, if you are grinding flax seed yourself make sure you feed it relatively quickly after grinding and if you are buying pre-ground flax seed make sure it has been stabilized. The omega-3 fatty acids tend to break down fairly easily after processing.