When foals are born, they have a very small amount of fat soluble vitamins in their system.  This is because the equine placenta prevents most fat soluble vitamins from crossing to the fetus during pregnancy.  The source these vitamins must then be the first milk, or colostrum.  Vitamin A is required for vision, reproduction, growth and development of epithelial cells and boney tissue.  Vitamin A deficiencies have been reported to cause decreased immunity, neurological disease, and congenital defects.  Vitamin E is an antioxidant and a deficiency of Vitamin E also causes a decrease in immunity as well as a form of muscular dystrophy in horses.  Vitamin A and E are both very abundant in high quality rapidly growing pastures, especially alfalfa.  However, as the quality of the pastures decrease, or the forage is processed into hay, the levels of these vitamins decrease. 

These vitamins must be supplemented in horses not on pasture.  To determine the amount of fat soluble vitamins in colostrum and the relationship to the mare’s diet, a study was performed at Virginia Tech on 9 foaling mares.  Concentrations of vitamins A and E were measured in the mare’s plasma and milk as well as in the foals.  It was determined that the current recommendations for the amount of vitamin A in the mare before and after foaling should be tripled.  Pregnant and lactating 1000 lb mares should receive around 15,000 units vitamin A per day in their total ration and that the most effective form of supplemental vitamin A is retinal palmitate.  It was also determined that current recommendations for Vitamin E only need to be increased by 20% up to approximately 1000 units per day.  The most effective form of Vitamin E is oral and natural d-alpha tocopherol.