What Does It Do?

B₂ is vital for protein and carbohydrate metabolism.  Riboflavin is a precursor to two coenzymes. Coenzymes are molecules that carry chemical compounds between two enzymes which transport many substances in the body. Being a precursor simply means that the equine body uses B₂ to make the coenzymes. B₂  also appears to have a role in fat metabolism.

There is a specific site in an area of the small intestine where dietary B₂  is absorbed.  It binds to a carrier protein and then is transported to the liver, the adrenals, and other sites where it is built into the enzymes.

As with all water soluble vitamins excess B₂  is withdrawn by the kidneys and excreted via the urine.

Nutritional Requirements:

At 30 mg per day a hard working adult horse has the highest demand for B₂  in its diet for proper metabolism.  Most adult horses should have a diet that provides between 9-15 mg of B₂  daily for optimal enzyme activity.  Young horses should get between 4-10 mg/day.

Despite its importance in the horse’s everyday life, B₂ intake is of little concern for the average horse owner. Because of the concentrations found in various forages, the horse easily meets the daily requirement of B₂.

Where Does My Horse Get B₂ ?

Legume forage like alfalfa and clover are the best sources of B₂  in the equine diet and contain around 15 mg/kg of dry matter.  Grass hay has about 7-10 mg/kg (dry matter) of B₂ so is also a great source.

Cereal grains and milling by-products meals are poor sources but some oil seeds and dried yeast/brewery/distillery products have higher contents.

The microbes in the large intestine can produce B₂  for the horse’s use. This was illustrated in one study when horses that were fed diets known to be in B₂ had increased B₂ concentrations in the cecum and colon.

What about B₂  Toxicity?

Since B₂  is one of the water-soluble vitamins any excess is rapidly excreted via the kidneys and urine. There is no evidence that the intake of excessive amounts of B₂  leads to any form of toxic reaction. Very large amounts have been supplied to horses and many other species without any apparent effect.

What about B₂  Deficiency?

One area of concern for deficiency is if the horse is not fed adequate forage which is just another example of why I am always preaching about forage. If a horse is fed a high energy diet of grains, that is not fortified, the ration will naturally be low in B₂ .

Therefore as the energy level of the diet is increased the B₂  level should be increased proportionally. Most commercially formulated feeds are fortified but a diet of whole grains like corn, oats, etc. without good hay or a vitamin supplement could create issues.

Mycotoxins which can be in contaminated feed and hay are another area of concern for B₂  levels.  Mycotoxis from mold have been found to reduce the effectiveness of the dietary B₂  supply. 

Even with these concerns, B₂  deficiency has never been reported in the horse.

~Peace and Good Feed,

The Nerd