HappyHOrseHealthyPlanet_B1 THIAMIN

What Does It Do?

The main function of thiamine is the metabolism of carbohydrates and protein.  Thiamin, known as B1 is required for fat metabolism as well.

There are three enzymes that require B1, they have big technical names that I won’t include here but they do have an important role in carbohydrate digestion, so I will mention them.

The first two help break down glucose and other similar substrates that will eventually become adenosine triphosphate (ATP). ATP is the energy that all of the cells in the equine body use to perform basically every function (eating, getting rid of waste, etc).

The third enzyme is involved in the pentose phosphate pathway which has several important roles.  The most important function of this pathway is to provide the cells with a specific sugar to make nucleic acids. Nucleic acids are what make up DNA, so this enzyme is also very important.

Put all the uses of B1 together and you can see it is a very important vitamin for your horse’s health and well-being.

Nutritional Requirements if B1:

Exact needs of B1 are not known but it is thought that 0.14 mg per kg of body weight is not sufficient and that 45 mg per g of body weight will result in normal food intake and weight gain. Knowing exact totals is not necessary to measure in horses however because they normally synthesize all the B-vitamins that they need.

In theory, if you have a heavily stressed horse, he might not be able at times to synthesize enough B-vitamins and therefore might need additional dietary B1.  For example, one of the difficulties we often see with hard working horses is keeping their appetite up so it might be beneficial to supplement with B1.  Other research suggests that increased B1 intake in growing horses appears to increase body weight gain.

Where Does My Horse Get B1?

The most significant source of this B vitamin in feedstuffs is brewers yeast with 95 mg/kg.  B1 is one of the few vitamins that is found in grains.  Of the cereal grains, barley contains the most with 5.7 mg/kg, followed by wheat, oats and then corn respectively.

scoop of grain horse feed

Grain by-products actually contain more B1 than the whole grains with rice bran having the most (23 mg/kg). Other grain by-products that are full of B1 are wheat midds and wheat bran.

A few protein sources also contain a good amount of B1. Peanut meal has 12 mg/kg and cottonseed meal has 6.4 mg/kg.

So when you check a label for ingredients look and see what sources of B1 might be in your grain or supplement.

Is there a Risk of B1Toxicity?

As with all water-soluble vitamins toxicity is not an issue. B1 is water soluble and to date there has never been a report of toxicity.  Generally speaking any extra that the horse doesn’t need is eliminated from the body through urine.

What about B1 Deficiency?

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

In rare cases where there is a B1 deficiency is you might see the disease beriberi.  Beriberi affects the nervous system and symptoms include pain in the limbs, edema (swelling of the body), and severe lethargy.

B1 deficiency has also been suggested as a factor in roaring, because some research has shown that roarers have lower blood thiamin levels than non-roarers.


Despite the seriousness of B1 deficiency, reasonable horses that are provided a decent equine diet high in good quality forage will have no problem obtaining their daily requirement of B1.

Side note: Even under the best conditions there is a way that horses can get deficient in B1 and that is by consuming bracken fern.  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.

Bracken Fern

~Peace and Good Feed,

The Nerd

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