Fat soluble vitamin derived from carotenoid pigments, principally beta carotene, in forages. Important for the maintenance of night vision as well as in reproductive function and epithelial cell production. Fresh pasture is an excellent source but after harvesting and drying to make hay the beta carotene content oxidizes, and the potency falls dramatically within a couple of months. Most manufactured feeds are consequently fortified with Vitamin A in the form of synthetic Retinyl Acetate or Palmitate.
Deficiency causes night blindness but is rare in horses under modern conditions as extremely low intake is required for it to occur. Excess tear formation precedes it, and long term deficiency may also impair normal uterine function and affect fertility. Horses stabled long term with no pasture access and fed aged hay would be most susceptible but in practical terms it would require extreme deprivation to produce clinical deficiency.