Vitamin requirements are affected by age, growth stage and stress, such as work load, travel and disease. In addition supplementation also depends upon dietary supply, microbial synthesis and absorption. They are needed in small amounts to promote and regulate several body functions.
All vitamins except A and E are produced in the body; vitamins D, C and niacin (a B group vitamin) are synthesized by the horse; all other B vitamins and vitamin K are synthesized by microbes in the cecum and large intestine. Vitamins are classed as fat-soluble (vitamins A, D, E &a