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Linseed, is it safe?

Some say linseeds/flax are poisonous and should never be fed in any form and others say the opposite. The current wisdom depends on who you ask!

Following is a comparison of views and what the scientific studies are showing: Dr Deb Bennett (biomechanics expert) advocates flax/linseed is a poison and should never be fed yet many nutritionists like Dr Eleanor Kellon VMD, Dr Susan Evans Garlinghouse VMD and Dr David Marlin advocate linseeds/flaxseeds are fine in reasonable amounts.

Dr Lydia Gray VMD states clearly on her ‘Askthevetpage blog’ that feeding flax/linseed is safe. Dr Gray says feeding linseed is harmless because “a recent study confirmed that stomach acid inactivates the enzymes that interact with the cyanogenic glycosides to form cyanide (also known as prussic acid) so that is why toxicity is not observed” and advises feeding the ground up seeds soon after grinding. Links are at the bottom of the page.

Dr David Marlin says that “the risk of hydrogen cyanide production is very low as once the linseed reaches the stomach the low pH (acidity) prevents the breakdown of cyanohydrins to hydrogen cyanide.”
Facebook 4 Nov 2019

Linseed or flax (Linum usitatissimum) is the only oil seed that contains the ratio of omega-3 fatty acids (anti inflammatory) to omega-6 fatty acids (pro inflammatory) in roughly the same ratio as grass, about 4:1. Linseed oil contains roughly 58% omega-3 and 14% omega-6 fatty acids depending on the analysis. Both omega-3 and 6 fatty acids are essential in the diet, they have to come from food sources whereas the other omega fatty acids such as 9 can be manufactured by the horse.

What about other oils?

Rice bran, sunflower seeds, canola, coconut, hemp, soybean oil and EVERY other oil are high in the pro inflammatory omega-6 compared to omega-3 fatty acids.  Both coconut and sunflower seeds contain essentially zero omega-3 fatty acids. I’ve even been asked about emu oil! Definitely not suitable for feeding horses, and the processing is not great for the emus. For a comparison of some of the choices:











The best oil is the one with the most alpha-linolenic acid (omega-3) vs linoleic acid (omega-6). Note that canola oil has the next best profile for omega-3 after linseed/flax but the amount is a lot less than the level of omega-6. The horse has no shortage of omega-6 fatty acids, the aim is to supplement as much omega-3 fatty acids.

Studies such as The Slow Discovery of the Importance of 3 Essential Fatty Acids in Human Health and The Benefits of Flaxseed explain in more detail about the benefits of omega-3 fatty acids. The study The effects of dietary N-3 and antioxidant supplementation on erythrocyte membrane fatty acid composition and fluidity in exercising horses documented the reduction in red blood cell deformity due to exercise with omega-3 fatty acid supplementation. Links at the bottom of the page.

Fat or oil in hays is roughly 50% of the level in fresh grass but the loss is almost entirely omega-3 as the fatty acids are heat sensitive. The curing process to turn grass into hay destroys the omega-3s. Linseed is mainly recommended as a fatty acid supplementation for horses on predominantly hay/supplementary feed diets as they miss out on the omega-3s.

Why is linseed a concern?

The seeds contain little, to no, preformed hydrogen cyanide but hydrogen cyanide, also known as prussic acid is produced when the enzyme, linamarase comes into contact with cyanogenic glycosides that are normally kept separated in the cell vesicles. This occurs with grinding or contact with water. Linamarase breaks down cyanogenic glycosides to cyanohydrins and then to hydrogen cyanide.

Strains of linseed used for human consumption typically have low levels of cyanogenic glycosides. Also, hydrogen cyanide is a gas and will vaporise off the meal as it is released from hydrocyanic acid. Heat treatment of the meal to lower the moisture content will also greatly decrease it. Freshly milled linseed meal may be as high as 500 ppm according to some EU sources, but this will drop even during the oil extraction process.

To put the risk in perspective, cattle and pigs have been fed diets containing as much as 15% linseed by weight with no toxicity. In Plants Causing Sudden Death, it was reported that ruminants like cattle “are more susceptible to cyanide poisoning than other animals” and that “Humans, pigs, dogs, and horses that have a highly acidic stomach (pH 2-4) tend to have a reduced rate of glycoside hydrolysis and cyanide production in their digestive systems and therefore rarely suffer from cyanide poisoning of plant origin”. Dr Kellon VMD said she has never ever seen a report of cyanide poisoning from linseed in a horse. The Canadian Sweet Itch study used human grade stabilised linseed, about 450 grams/450 kg bodyweight per day and reported no issues. This page has tips for Queensland Itch remedies.

It has to be a personal decision by the horse owner about what they feel comfortable feeding. If not comfortable with grinding the seeds then simply use linseed oil as the cyanogenic glycosides and enzymes are not in the oil component of the seed, the oil is definitely safe. Look for cold pressed or animal grade linseeds. Cold pressed/animal grade means the oil has been squeezed out of the seeds without heating the seeds as heat can destroy the fatty acids. The oil to avoid is furniture grade linseed oil as it contains solvents to expediate the drying time when used on furniture, tool handles. A good reference to read about furniture grade linseed is at The Natural Handyman website, link below. If you buy linseed oil from a hardware, assume it’s for furniture, and toxic for horses.

Unprocessed oils frequently have opaque, thick yellow material in the bottom. This is lignans and other material from the linseed, rich in plant antioxidants and vitamin E. If the oil is not refrigerated there will be a rapid loss of omega-3s although there may be some protection from the natural antioxidants.

Boiling linseeds will destroy the omega fatty acids, if the purpose was to supplement omega-3s then boiling makes it pointless. However heating in an oven up to 150°C, ground in a blender and storing for one month was found to not degrade the omega-3 fatty acids in this study; Heat Treatment and Thirty-Day Storage Period Do Not Affect the Stability of Omega-3 Fatty Acid in Brown Flaxseed (Linum Usitatissimum) Whole Flour. 

It has been widely believed for a long time that the seeds need to be freshly ground in a blender or coffee grinder just before feeding. At this stage there has been no studies done on how well linseeds are digested and the omega-3 fatty acids absorbed if not ground. Some people have been stating that the linseeds do not require grinding and have been feeding the seeds whole. One way to find out is to remove any seeds in the manure and place in a glass of vinegar or even milk. If a mucilage or gel forms, then the seeds haven’t been broken down properly. Another way is to observe whether a crop of linseed plants germinate in the manure though the limitations to this is that the right environmental conditions also need to be met for the seeds to germinate. Horses with compromised dentition and older horses are unlikely to benefit from whole linseeds.

Do you need to supplement omega-3 fatty acids?

If your horses are predominantly on pasture then no, your horses are likely to be getting plentiful anti inflammatory omega-3 fatty acids from grass. If your horses have hay and any other supplementary feeds as the main forage then the answer is yes as curing hay destroys the omega-3 fatty acids. The only feed that comes out of a bag that is high in omega-3 fatty acids is linseed (flax seed) or chia seeds.

For insulin resistant (IR) horses, some studies have shown that supplementation with omega-3 fatty acids have demonstrated an ability to increase insulin sensitivity though more research is required with larger numbers of IR horses. The study Effects of Ω-3 (n-3) fatty acid supplementation on insulin sensitivity in horses is one example, link below.

Linseed vs Chia seeds

Chia seeds can be fed instead of linseeds. Chia is a good source of omega-3 fatty acids though contain less per kg than linseeds and the omega-3 to omega-6 ratio is less too. It’s recommended that chia seeds do not require grinding despite being smaller than linseeds as the seed coat is softer. This is a big advantage advantage compared to linseed though unfortunately chia seeds are a lot more expensive.

A Effects of Ω-3 (n-3) fatty acid supplementation on insulin sensitivity in horses looked at the composition of fatty acids in flax, linseed and perilla seeds. Conversion factor for omega-3 fatty acids is roughly 1.25 depending on the cultivar. Multiply the amount of linseeds by 1.25 to get the equivalent amount of chia seeds.
For example: 100 grams linseed is approximately equivalent in omega-3 fatty acids to 125 grams chia seeds.

Fish oil vs Linseeds

There are 3 major types of the anti inflammatory omega-3 fatty acids; alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). These are essential fatty acids, they have to come from the diet for people so human studies looks at the three and how they work in our bodies. There are lots of benefits. Once eaten the body converts ALA to EPA and DHA, the two types of omega-3 fatty acids more readily used by us. Fish get their ALA from plant material and convert it to EPA and DHA. Plant based omega-6 is called linoleic acid.

Plant material is a rich source of ALA but does not contain preformed EPA or DHA. Since a horse’s natural diet is plant material and not fish I find it puzzling that companies are pushing fish oil which is highly unpalatable for horses unless heavily processed. The Kentucky Equine Research article (link below) is a great example of how companies push fish oil as a feed additive for horses.

The article above says that that the ability of horses to efficiently convert ALA to EPA and DHA is not known, and thus requires more research.

Whether ALA can convert efficiently into EPA or DHA or not is of lesser importance to me if a herbivore like the horse didn’t evolve on a diet that included EPA or DHA. It’s a personal choice whether to include fish in a horse’s diet. Fish oil is well established as beneficial for people which makes a lot of sense since we are omnivores. The ideal ratio of omega-3 to omega-6 fatty acids is higher in omega-6 in animals like us that are higher up in the food chain.

Further reading:

Links may change over time. If a link doesn’t work, search the title in your search engine.

Oil chart and more detailed downloadable pdf:

Alonzy J Linseed Oil – It’s Use and Limitations The Natural Handyman

Dr Eleanor Kellon VMD

Dr Lydia Gray VMD Is Flax Seed Safe to Use in Horses?

Garton, GH (1960) Fatty Acid Composition of the Lipids of Pasture Grasses Nature 187:511-512

Hess TM, Rexford J, Hansen DK, Ahrens NS, Harris M, Engle T, Ross T and Allen KG (2013) Effects of Ω-3 (n-3) fatty acid supplementation on insulin sensitivity in horses J. Equine Vet. Sci. 33:446-453

Holman RT (1998) The slow discovery of the importance of 3 essential fatty acids in human health J. Nut. Feb;128(2):427S-433S

Knight AP and Walter RG (2002) Plants Causing Sudden Death In: A Guide to Plant Poisoning of Animals in North America;jsessionid=53B006B32EDF5FFAC29E80B8D00A5544?doi=

Portier K, De Moffarts B, Fellman N, Kirschvink N, Motta C, Letellier C, Ruelland A, Van Erckt E, Lekeux P and Coudert J. (2006) The effects of dietary N-3 and antioxidant supplementation on erythrocyte membrane fatty acid composition and fluidity in exercising horses EEP 7 Equine Vet. J 36

Magee E. The Benefits of Flaxseed

Morais D de C, Moraes EA, Dantas MI de S et al. (2011) Heat treatment and thirty-day storage period so not affect the stability of omega-3 fatty acid in brown flaxseed (Linum usitatissimum) whole flour. Food Nut. Sci. Jun;2(4):281-286

DHA/EPA Omega-3 Institute. Metabolism of Omega-6 and Omega-3 Fatty Acids and the Omega-6:Omega-3 Ratio

Kentucky Equine Research Inc (2009) Omega-3 Fatty Acids: Consider the Source

Maddock TD, Anderson VL, Lardy GP (2005) Using flax in livestock diets. NDSU Extension Service, North Dakota State University

O’Neill W, McKee S, and Clarke AF (2002) Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity Can. J. Vet. Res. Oct;66(4):272-277

Rudzińska M (2012)Lipid components of flax, perilla, and chia seeds Eur. J. Lipid Sci. Tech. Jul;114(7):794-800


Chart is linked to a more detailed oil chart, provided by the website. 

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