Feeding Flaxseed

Flaxseed (also known as linseed) is a valued feed ingredient amongst horse people. How it should be used has long been the subject of considerable debate. Its safety for horses has always been under question and methods of preparation are many and varied. This article looks at what flaxseed can add to your horse’s diet, if it is safe to feed and how it can be prepared for feeding.

What does flax add to a diet?

Flaxseed’s best known attribute is its high Omega 3 essential fatty acid content. Flaxseeds are over 40% oil and more than 50% of this oil is the omega 3 fatty acid α‐linolenic acid. A horse’s natural grazing diet is high in omega 3 fatty acids. However as we add grains like corn and barley to a horse’s diet their diet can become skewed towards having high levels of omega 6 fatty acids. Flaxseed provides a ‘natural’ way to keep the levels of omega 3 in a horse’s diet balanced without using expensive omega 3 fatty acid supplements. Adding 100 grams of flaxseed to your horse’s diet will add over 20 ml of omega 3 fatty acids.

While omega 3 fatty acids are generally the primary reason flaxseeds are fed to a horse, flaxseeds are a decent source of protein with around 24% protein and 0.9% lysine and also contain around 25% fibre.

When can flaxseed be used?

Flaxseed is useful for horses on a high grain (and therefore high omega 6 fatty acid) diet or when they are eating hay that has been in storage for some time or grazing low quality pasture. Flaxseed may also be used when horses have a dry coat and skin, if they have problems with inflammation including arthritis and sweet itch/Queensland itch or when high omega 6 oils like corn oil or sunflower oil are being fed as an energy source in the diet. Flaxseed itself can be used as a source of energy in the diet and because of its high fat attribute is often found in supplements intended to promote weight gain in horses.

How should flaxseed be prepared for feeding?

Because flaxseed is such a small seed it is best to grind flaxseeds immediately prior to feeding to break the seed coat, otherwise the seeds will pass undigested all the way through the gastrointestinal tract. It is important to grind the seeds fresh just prior to feeding as the oils in flaxseed are prone to rancidity and will go off very quickly if ground and left exposed to air. A small coffee grinder is commonly used for the purpose of grinding fresh flax straight into a horse’s feed (very gourmet!).

It is possible to purchase pre‐ground and stabilised flaxseeds if grinding your own is not an option.

Does Flaxseed have to be boiled before feeding?

Tradition says that flaxseed must be boiled before feeding it to a horse because of the risk of Prussic Acid (or hydrogen cyanide) poisoning. Anyone who has boiled flaxseed knows how messy it gets and for most the effort and mess are too much to continue persisting. Well good news … flaxseed it seems can be fed safely without being boiled.

Flaxseed contains compounds called cyanogenic glycosides. When the flaxseeds are chewed up by a horse these cyanogenic glycosides come into contact with an enzyme (β‐glycosidase) which converts it to hydrogen cyanide, which can then lead to cyanide poisoning. HOWEVER, the β‐glycosidase enzyme is destroyed by the acidic environment of the horse’s gastric stomach, meaning the cyanide is never produced in quantities large enough to cause any problems. This means you can feed flaxseed without cooking it first.

A study published in the Canadian Journal of Veterinary Research in 2002 looking at the ability of flaxseed to reduce the inflammation associated with culicoides hypersensitivity (sweet itch or Queensland itch) reported that they fed 1 lb of flaxseed per 1000 lb of bodyweight to horses (or 0.5 kg per 500 kg bodyweight) over a period of 42 days with no negative side‐effects being observed. With this dose rate being much higher than the normal 1 to 2 cups fed per day it can be concluded that flaxseed is safe to feed to horses without cooking it first.

What about soaking it?

It is possible that soaking flaxseed may actually make it dangerous as soaking the seeds would, to some extent, allow the β‐glycosidase enzyme to come into contact with the cyanogenic glycosides and allow for the production of hydrogen cyanide. So it is recommended you do not soak flaxseed before feeding.

Can flaxseed meal be fed?

Flaxseed meal is the high protein (32%) meal left over after the flaxseed oil has been extracted from the seed. Flaxseed meal can be fed to horses, however because the meal has had most of the oil extracted its primary use in a horse’s diet is as a protein supplement. The risk of cyanide poisoning from flaxseed meal is a little unclear. Because the seed is crushed during the oil extraction process it is possible for the β‐ glycosidase enzyme to come into contact with the cyanogenic glycosides, so it is likely hydrogen cyanide will be present. If you wish to feed flaxseed meal, look for meal produced using heat extraction technology as opposed to meal made from seeds that were cold pressed. There are however far better sources of quality protein available including lupins, full fat soybean, soybean meal and canola meal, without the possible risk associated with flaxseed meal.

Other possible side effects

Flaxseed contains phytoestrogens. Phytoestrogens are naturally occurring plant compounds that are structurally similar to estrogen. Studies in rats (Collins et al 2003) have found that feeding high levels of flaxseed to rats increased the number of female rats with irregular estrous cycles, suggesting flax could have a negative impact on the fertility of breeding animals. If you are breeding your mares and having any type of fertility problems it would be wise to avoid flaxseed in their diets.


Flaxseed is a useful feed ingredient for horses. It can be used to increase a horse’s omega 3 essential fatty acid intake where dietary omega 3 levels are low or when higher intakes of omega 3 for a particular horse seem beneficial. Despite popular opinion that flaxseed must be cooked prior to feeding to avoid hydrogen cyanide poisoning, studies have shown that up to 1 lb/1000 lb bodyweight (or 0.5 kg/500 kg BW) can be safely fed without cooking. Flaxseed should not be soaked prior to feeding and they should be avoided in the diets of breeding mares with a history of reproduction problems. FeedXL can be used to incorporate flaxseed into your horse’s diet so that it balances well with other feed ingredients being fed.


Dr. Nerida Richards is FeedXL’s resident equine nutrition specialist. With a degree in Rural Science, a doctorate degree in equine nutrition and nearly 20 years of full time, on the ground experience in feeding all types of horses Nerida is able to help FeedXL members solve any problem they may come up against with feeding their horses. To learn more about Nerida and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.


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Seaweed for Horses: Miracle Supplement or Massive Con?

There has been much debate about the potential benefits to be gained from feeding seaweed to horses. On one side, we have seaweed being reported as a multifunctional supplement that will act as an anthelmintic, antacid, immuno-stimulator, anti-inflammatory, anti-cancer, anti-bacterial, anti-ulcer, heavy metal scavenger, fertility enhancer, nerve calmer, thyroid stimulator and skin and coat conditioner. From the other side, seaweed is called nothing more than a con, containing potentially dangerous levels of iodine and precious little of anything else. So who is right, and is there any middle ground to be sought in this argument?

What is Seaweed?

Seaweed is a marine plant that can be found in oceans all around the world. There are approximately 1700 different varieties of seaweed and they come in three different colours; green, brown and red. The green seaweeds generally grow close to the water’s surface and are smaller than the brown and red varieties. Brown seaweed grows in slightly deeper and often cold waters, while the red seaweeds grow in very deep waters. It is the brown seaweed (also called Kelp) that is commonly fed to horses in Australia.

Why Seaweed for horses?

Generally people will add seaweed to their horse’s feed to supply trace minerals that are lacking in the pasture, hay and concentrates being fed to the horse. Effectively, seaweed is used as a trace mineral supplement.

Is Seaweed a Good Trace Mineral Supplement?

Seaweed supporters will readily tell you that seaweed contains ‘every nutrient needed by the horse’ including 48 minerals, 16 amino acids and 11 vitamins, making it sound like a very attractive and natural option for trace mineral supplementation. However, the concentration of minerals in seaweed is so low that when fed at the levels generally recommended for horses (15 to 30 grams/day) it makes virtually no contribution to satisfying a horse’s trace mineral requirements, with the exception of iodine (Table 1).

Table 1: The percent of daily nutrient requirements for a 500 kg horse in light work satisfied by 20 grams of seaweed containing 600 mg/kg of iodine or by 20 grams of a well formulated commercial trace mineral supplement.

% of daily requirement
satisfied by 20 g of
% of daily requirement
satisfied by 20 g of a
commercial trace
mineral supplement
Copper 0.01 62
Zinc 0.06 44
Selenium 0.1 52
Manganese 0.05 44
Iodine 706 68
Iron 1.96 35

When it comes down to it, seaweed gives your horse very little benefit from a trace mineral perspective (with the exception of iodine, which is grossly oversupplied), particularly when considered in comparison with a well formulated commercial supplement.

How Much Iodine Does Seaweed Contain?

The iodine concentration of seaweed is generally highly variable and depends on many factors including the variety of seaweed and the age of the blades that were harvested and analysed. In a study conducted in 2004 (Teas et al.) researchers found that the concentration of iodine in 12 different seaweeds varied from 16 mg/kg to 8165 mg/kg. They also found that within the same variety of seaweed, iodine concentration ranged from 514 mg/kg of iodine in the older sun‐bleached blades to 6571 mg/kg in the juvenile, fresh blades, demonstrating the highly variable concentrations of iodine that may be present in a seaweed product.

How Much Iodine Do Horses Need?

Horses require between 0.35 and 0.4 mg of iodine/kg of dry matter consumed per day. Thus a 500 kg horse consuming 2% of its body weight in feed per day will need between 3.5 and 4 mg of iodine per day. Iodine toxicity will occur at intakes of 5 mg/kg of dry matter consumed per day, which is equal to approximately 50 mg/day for a 500 kg horse.

Can Seaweed Cause Iodine Toxicity?

YES! Iodine toxicities can definitely occur when horses are fed too much seaweed. So, how much seaweed is too much? Well, that all depends on the concentration of iodine in the seaweed. Eighty grams of seaweed that contains 600 mg/kg of iodine will need to be fed to cause acute iodine toxicity in a 500 kg horse, while just 6 grams of seaweed containing 8000 mg of iodine/kg will cause acute toxicity in the same horse.

Chronic toxicity may also be a problem in horses. The effects of feeding relatively high concentrations of iodine to a horse over a long period of time (for example you may feed 20 grams per day of a 600 mg/kg iodine seaweed for 6 months, providing your horse that has a requirement of 2 mg of iodine/day with 12 mg of iodine per day) have never been studied in horses. Studies in humans however (Pearce et al. 2002; Mizukami et al. 1993) have shown that iodine toxicity can be precipitated through long term exposure to moderately high concentrations of dietary iodine. Thus the answer to the question ‘how much is too much?’ is ‘we don’t know’, meaning seaweed must be fed with extreme caution, if it is to be fed at all.

Is There Any Time That Seaweed Is Useful in a Horse’s Diet?

Given the high iodine concentration in seaweed, it can be useful to feed as an iodine supplement when there is a demonstrated iodine deficiency. Remember that an iodine deficiency will cause virtually exactly the same symptoms as an iodine toxicity (goitre, a dry, lustreless coat, lethargy, dullness, drowsiness and timidity, inappetence and cold intolerance). Thus the only way to diagnose and differentiate an iodine deficiency from toxicity is to carefully analyse the iodine content of the feeds your horse is eating. If an iodine deficiency is diagnosed and you decide to feed seaweed, carefully calculate the amount required by your horse using the iodine concentration specified on the particular product you are using. Do not overfeed seaweed in an attempt to rapidly correct your horse’s iodine deficiency as you will end up correcting the deficiency only to cause a damaging toxicity.

4 Things You Must Do Before You Feed Seaweed to Your Horse

  1. Consider exactly why you want to feed seaweed. If you can’t pinpoint a good reason such as a demonstrated iodine deficiency, then it is probably best you don’t feed seaweed at all.
  2. Obtain the iodine content of the seaweed product you wish to use. If the product you are considering does not specify its iodine content do not feed it. Never feed your horse anything unless you know what is in it. If you have your seaweed tested for iodine concentration, send us the analysis at FeedXL and we can put your specific analysis with the tested iodine level into your personal FeedXL database.
  3. Using the products specified iodine concentration, calculate how much you need to feed per day to satisfy but not substantially exceed your horse’s iodine requirements. When using FeedXL, this is easy. Simply put enough seaweed meal into your horse’s diet to meet the calculated iodine requirement. No pen and calculator required.
    FeedXL will also make sure that if your horse is being fed other iodine-containing supplements these are taken into account.
  4. Carefully weigh and feed the calculated amount of seaweed to your horse each day. Never give your horse free access to seaweed; this will just be an iodine toxicity waiting to happen.

A Special Note about Seaweed for Mares and Foals

There is a particular risk in feeding seaweed to pregnant and lactating mares. Excess dietary iodine accumulates in the placenta and is excreted in milk. Thus foals born to mares consuming diets high in iodine will be at risk of developing iodine toxicity. Foals from these mares may be born dead, or very weak, with a poor suckle response. Those who live and continue to suckle from their dam will likely develop skeletal abnormalities as iodine toxicity causes low serum thyroxine hormone concentrations and the thyroxine hormone is crucial for cartilage maturation and bone formation.

The Final Slime…

Think carefully about feeding seaweed to your horse. If your horse doesn’t need additional iodine in its diet then I would suggest you don’t feed seaweed. If you do decide to feed it, do so with extreme caution, ensuring that you always use FeedXL to calculate the amount to feed and weigh and feed that amount accurately. Don’t guess, it’s definitely not good for your horse’s health!


Dr. Nerida Richards is FeedXL’s resident equine nutrition specialist. With a degree in Rural Science, a doctorate degree in equine nutrition and nearly 20 years of full time, on the ground experience in feeding all types of horses Nerida is able to help FeedXL members solve any problem they may come up against with feeding their horses. To learn more about Nerida and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.


Click here to join our ‘FeedXL Horse Nutrition Forum’ on Facebook

Grains for Horses: Cooked or Uncooked?

While a lot of time is spent focussed on horses that can’t eat grain in their diet, cereal grains such as oats, barley, triticale, corn, rice, rye, sorghum and wheat form a valuable component of many horse’s rations. Selecting the most digestible grain based feed however can be confusing, with uncooked grains like whole, cracked and crushed grains being available as well as cooked grains like extruded, micronised, steam rolled or steam flaked and pelleted grains.

The question is, which form of grain is best for your horse, cooked or uncooked?

Why we cook grains

Grains are fed primarily as a source of energy in a horse’s diet and that energy is derived mainly from the white starch found in the centre of the grain. For the horse to obtain the energy from the starch it must be digested by enzymes in the small intestine.

But digesting the starch to extract the energy is not easy for the horse because it is “packaged” within the grain in a way that makes it difficult for the horse to get to. The reason grains are cooked is to make access to the starch a lot easier for the horse.

How starch is “packaged”

Starch is simply many glucose molecules all bonded together and bundled up into starch granules. These starch granules are then embedded amongst protein in a structure known as the protein matrix (Figure 1).


Figure 1: A scanning electron micrograph of the middle of a barley grain showing the starch granules embedded within the protein matrix. The starch granules are the large round objects.


The starch granules, embedded in the protein, are then encased within individual endosperm cells and protected by a cell wall. Many of these cells are packed tightly within the grain’s starchy endosperm (the white bit found in the middle of a grain). And the endosperm itself is protected by the aleurone layer and finally the entire structure is covered by the seed coat (Figure 2). Now from the plant’s perspective, all of this packaging is absolutely critical for its survival and is designed to protect the plant embryo and its stored sources of energy and protein to ensure it will be able to grow and survive for the first few days following germination.


Figure 2: The location of starch granules (stained black) within the endosperm cells of barley grain surrounded by the protein matrix (stained green) and protected by the aleurone layer and seed coat.


So, the packaging is clever and essential from the plant’s perspective, however for the horse, all of this packaging is just a nuisance and prevents the horse from being able to digest and extract the energy from the grain. In fact, this packaging was actually specifically designed to allow a grain to pass through the gastrointestinal tract of an animal undamaged so it may germinate when it is excreted in the manure.

How does this packaging stop starch digestion?

The packaging can be likened to a security system at a casino which prevents the thieves (or in this case the enzymes) from stealing the cash (the starch). To digest the starch the enzymes in the horse’s small intestine must first breech the seed coat, then penetrate the aleurone layer. Following this they need to be able to make their way through the endosperm cell walls (these are the cells that contain the starch), then burrow through the sometimes impenetrable vault of the protein matrix before finally reaching the starch granule. Then, in a cruel twist of fate, if the enzyme reaches this far, it will find that the starch is bundled so tightly into a ball that the enzymes cannot digest it. So the horse is presented with a difficult hurdle—just how does it go about extracting the energy held in the starch of cereal grains?

Enter cooked grains…

It has been recognised for many years now that to effectively digest cereal grains, horses need some help. And that help comes in the form of ‘cooking’. Cooking grains using processes like extrusion, micronising and steam flaking breaks down the barriers the enzymes have to face in reaching and digesting cereal grain starch.

How cooking helps

When grains are cooked using a combination of heat, moisture, pressure and some form of physical process like rolling or grinding, the entire structure of the grain is disrupted. To start, the seed coat and aleurone layer are broken and the endosperm cell walls are opened up. In addition, the structure of the protein matrix is physically disrupted so it is no longer able to protect the starch granules. Cooking also turns the ordered and tightly packed structure of the starch granule into an open and vulnerable structure which can be easily attacked by enzymes in a process known as gelatinisation. Cooking simply gives the horse’s enzymes access to the grain starch so they can go about their work of cutting up the starch into single glucose molecules, which the horse then absorbs from the small intestine into the body, where it is used for energy.

What about cracked grains?

Simply cracking, crushing or grinding grains is the same process as chewing and aims only to change the physical structure of the grain, breaking the seed coat and reducing the grains particle size to give the enzymes better access to the starch within the centre of the grain. While the seed coat and aleurone layer barriers are removed, physical processing only causes minor damage to the endosperm cell walls and leaves a majority of the protein matrix and starch granule structure intact, meaning only small improvements to starch digestion will be made. Work conducted in horses showed that cracking corn only improved its digestibility in the small intestine of the horse by 1%. So while physical processing can get an enzyme through the front doors of the casino, gives them access to some of the cash floating around at the tables, and maybe even gets them into the strong room, it leaves the enzymes without a key, security code or set of explosives to get it into the vault. In short, they aren’t much better than whole grains.

Does soaking grains help?

Soaking grains simply makes them much easier to chew, so soaking will help the horse to break the seed coat and aleurone layer barriers. However soaking does nothing to disrupt the endosperm cell wall, protein matrix or starch granule structure, so, like cracking grains, soaking does not help to improve starch digestion.

What happens if cereal grains are fed without being cooked?

Starch from grains fed whole or cracked will remain largely undigested as it passes through the small intestine and will eventually be delivered to the hindgut. This is where the trouble begins. The bacteria in the hindgut do not face the same barriers as the enzymes in the small intestine, and they are able to reach and rapidly ferment the starch contained in uncooked grains. This rapid fermentation of starch causes excessive production of acids, which accumulate in the hindgut and lower the hindgut pH (the hindgut contents become acidic). Low pH in the horse’s hindgut causes a multitude of diseases and behavioural disturbances including laminitis, colic, endotoxaemia, systemic acidosis, reduced fibre fermentation, poorappetite, wood chewing and the eating of bedding as well as deficiencies in the B-group vitamins (including biotin) and vitamin K.

What about oats?

The general consensus is that oats can be fed unprocessed. As it is a larger grain, horses are capable of chewing the grain enough to break its seed coat, removing the need for physical processing. Studies have also found that oat starch is far easier to digest than corn or barley starch in an uncooked form. So oats can be fed whole and uncooked. However, whether oats can be fed unprocessed needs to be decided on a horse by horse basis. Observe your horse’s manure closely when you are feeding him oats. If you observe whole oat grains in his manure, whole oats is not a suitable feed for this horse. It is important to make sure the oats you are observing in the manure are whole and not just undigested hulls. Do this by taking them from the manure and squeezing them. If they are whole you will observe the white starch oozing from the centre. If you want to feed oats specifically, but your horse doesn’t digest them well, cracked, steam rolled and micronised oats can be purchased.

And the moral of the story…

Don’t feed cereal grains unless they have been cooked, with the exception of oats for some horses. If you feed whole, uncooked cereal grains, your horse will get little benefit from them and they have a good chance of causing disease and behavioural problems. Remember, the reason you feed cereal grains is to provide your horse with a source of energy. Most of this energy is held within the grain’s starch. If the horse can’t digest this starch, then you are better off not feeding the grain at all.


Dr. Nerida Richards is FeedXL’s resident equine nutrition specialist. With a degree in Rural Science, a doctorate degree in equine nutrition and nearly 20 years of full time, on the ground experience in feeding all types of horses Nerida is able to help FeedXL members solve any problem they may come up against with feeding their horses. To learn more about Nerida and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.


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Biotin: Should You Supplement?

Biotin is a vitamin essential for many functions in a horse’s body, including: fatty acid synthesis, protein and energy metabolism and cell proliferation.

In equine nutrition biotin is best known and most commonly used to positively influence hoof quality. There are many biotin supplements available. Some contain only biotin, others also have nutrients like methionine and organic zinc. These supplements are marketed as hoof supplements and the one thing they usually have in common is they are expensive. The question is, does your horse actually need supplemental biotin?

Biotin is naturally available to your horse

Your horse has access to two sources of natural biotin. Biotin is contained in most feeds and forages, particularly green fresh forages. In addition, the bacteria in a healthy horse’s gut produce biotin which is made available to the horse.

Therefore a horse on a forage based diet with a healthy gut should not need to be supplemented with biotin. BUT there are plenty of horses on this type of diet with poor quality hooves. Often horse owners turn straight to biotin in this situation to improve hoof quality. However, it is unlikely a biotin deficiency is causing the problem, which means biotin certainly isn’t going to fix it.

An unbalanced diet causes poor quality hooves

While supplementing with biotin may seem a good solution to improve hoof quality, it won’t help if the rest of the diet is unbalanced. Minerals like copper and zinc and good quality protein all need to be in the horse’s diet in balanced quantities for the horse to grow quality hoof.

The best way to achieve good quality hooves

Feed a completely balanced diet! If your horse has poor quality hooves it is likely its diet is missing something and it probably isn’t biotin. Steps to achieving good quality hooves are:

  1. Balance your horse’s diet using FeedXL and feed that balanced diet. It will be 3 to 6 months before you see a positive effect.
  2. Base your horse’s diet as much as possible on good quality forage.
  3. Avoid feeding uncooked grains (with the exception of oats) as these can upset the bacteria balance in the hindgut and reduce their natural production of biotin.

When should you use biotin?

There are some situations that may warrant biotin supplementation. These are:

  1. If your horse has been maintained on a high grain diet for an extended period of time.
  2. If your horse has been on a long term dose of oral antibiotic.
  3. If your horse is old and has lost some function in its hindgut.
  4. If your horse is recovering from a condition like laminitis or an injury that has affected its hooves
  5. If your horse has been on a long-term balanced diet and you are still not happy with the condition of his hooves, biotin may help!

If any of these situations apply to your horse and its hoof quality is poor despite a balanced diet it is possible that it is not receiving enough biotin. FeedXL will work out the best dose for your horse so that supplementing is effective. As a guide, a 500 kg (1100 lb) horse will need 20 mg of biotin per day and you will need to supplement for around 6 months for it to really work.


Dr. Nerida Richards is FeedXL’s resident equine nutrition specialist. With a degree in Rural Science, a doctorate degree in equine nutrition and nearly 20 years of full time, on the ground experience in feeding all types of horses Nerida is able to help FeedXL members solve any problem they may come up against with feeding their horses. To learn more about Nerida and to ‘meet’ the rest of the FeedXL team, check out our About Us page here.


Click here to join us on our Facebook Page

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