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As with all water soluble vitamins excess B2 is withdrawn by the kidneys and excreted via the urine.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