Thiamin: Vitamin B₁

Thiamin, one of the B vitamins (B₁ to be exact), is very important for carbohydrate digestion.

There are three enzymes that require B₁:

  • pyruvate dehydrogenase
  • alpha-ketoglutarate dehydrogenase
  • transketolase

They have big technical names (don't worry about them -- I just provided them for those who want them) but they do have an important role in carbohydrate digestion, so we're talking about them.

The first two, pyruvate dehydrogenase and alpha-ketoglutarate dehyrdrogenase, help metabolize (break down) substrates that will eventually become adenosine triphosphate (ATP). These substrates include glucose and other similar substrates.

ATP is the energy that all of the cells in the equine body (and yours!) use to perform basic functions such as eating, getting rid of waste, protecting themselves, and pretty much everything else. Pretty important stuff...no ATP, no cells, no horse.

The last one, transketolase, is involved in the pentose phosphate pathway.

This pathway has a few important functions -- it produces reducing equivalents (NADPH) for reactions within cells. This is another one of those things that it is not essential to understand -- just know that its very important!

The second function of this pathway is to provide the cells with a specific sugar -- ribose-5-phosphate (R5P) -- to make nucleic acids. Nucleic acids are what make up DNA, so this function of the pathway is also very important.

Put all the uses of thiamin together and you can see it is a very important vitamin for your horse's health and well-being.

Sources of Thiamin

Since we now know that this vitamin is so important to your horse's health, let's take a look at where he can get it from.

B₁ is one of the few vitamins that is found in significant quantities in cereal grains.

Of the cereal grains, barley contains the most, with 5.7 mg/kg. Following barley, wheat comes in second, then oats and lastly corn.

But, as usual, the cereal grains are not the greatest source of B₁. Cereal grain by-products also contain significant amounts of this vitamin. Rice bran comes in highest of the by-products, with 23 mg/kg, more than 3 times the amount found in the highest cereal grain. Following rice bran we have:

  • Wheat middlings -- 12 mg/kg
  • Wheat bran -- 8 mg/kg

Protein sources also contain a good amount of B₁ (peanut meal 12 mg/kg and cottonseed meal 6.4 mg/kg) but the most significant source of this B vitamin is brewers yeast. It comes in at a whopping 95 mg/kg!

As a recap, here's a table of all those sources:

Dietary Source B₁ Content
Brewer's Yeast 95 mg/kg
Rice Bran 23 mg/kg
Wheat Middlings 12 mg/kg
Peanut Meal 12 mg/kg
Wheat Bran 8 mg/kg
Cottonseed Meal 6.4 mg/kg
Barley 5.7 mg/kg
Wheat 5.5 mg/kg
Oats 5.2 mg/kg
Corn 3.5 mg/kg

Thiamin Toxicity

Due to thiamin being a B-vitamin, which are all water-soluble, toxicity is not an issue.

To date there has never been a report of toxicity, and it does not seem as a likely possibility.

Thiamin Deficiency

B₁ deficiency is much more a concern than toxicity due to the severity of the symptoms. Water-soluble vitamins are not stored in the body, therefore must be consumed on a daily basis in adequate amounts.

The most classical symptom of thiamin deficiency is beriberi. Beriberi is a nasty disease of the nervous system. Complications often affect the heart, nervous system, muslces, and digestive system.

Symptoms of beriberi include pain in the limbs, edema (swelling of the body), and severe lethargy.

Other symptoms of deficiency that have been seen in horses include:

  • Loss of appetite
  • Anorexia
  • Bradycardia (a slow heartbeat)
  • Muscle twitching
  • Ataxia (severe lack of coordination)

Despite the seriousness of B₁ deficiency, horses kept under reasonable conditions and fed an average diet will have no problem obtaining their daily requirement of B₁.

However, horse owners should be very aware of any bracken fern (pictured below) that may be within pastures or other areas horses have access to.

bracken fern can cause thiamin deficiency symtoms



Horses that consume bracken fern may display signs of B₁ deficiency despite having adequate amounts in the diet. This is because bracken fern blocks the metabolism of B₁ in the horse.

Another substance that blocks B₁ metabolism is amprolium. Amprolium is used in veterinary medicine to treat Isospora bacterial infections in dogs and cats and Eimeria bacterial infections in cattle and poultry. It is marketed under the names of Corid and Amprol.

In small doses, it will not affect horses negatively, but if your horse gets into some and consumes large amounts, it could be a problem.

Dietary Requirements

The B₁ requirement for horses depends on their workload. Working horses require at least 5 mg/kg dry matter, and all others require at least 3 mg/kg dry matter.

Increased B₁ intake in growing horses appears to increase body weight gain.


Thiamin is a very important B vitamin for your horse. Thankfully it is also easily found in most horse's diets. Consequences of deficiency are severe, but in practical horse keeping situations, are of little concern.


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