The purpose of this study was to examine vitamin A and E in equine nutrition and especially in relation to forages. A literature review was conducted to examine factors that influence the level of vitamins present in forage, the vitamin A and E requirement of horses, and the absorption of vitamin A and E in horses. The influence of DM level on alpha-tocopherol and beta-carotene content in ensiled forage was investigated in a controlled ensiling study using baled silage and haylage. The results from the ensiling study were combined with data of vitamin A and E concentrations collected from literature. Calculations were done to theoretically establish how well the vitamin content in ensiled forage can cover the
maintenance requirements of vitamin A and E in horses. This study subsequently showed that no larger losses of alpha-tocopherol or beta-carotene occured when conserving forage as silage, when compared to conserving the same forage as haylage. The beta-carotene content of all silages and haylages in this study showed that the level of beta-carotene was sufficient to cover the vitamin requirement of all categories of horses. However, the alpha-tocopherol contents would struggle to cover the requirements of all horse categories.
Additionally, a survey was conducted to investigate the habits of Swedish horse-owners in supplying vitamin supplements to their horses, as well as the reasons why they purchased and used particular vitamin supplements. The survey was based on 1049 horses. During the summer period, 45% of the horses were allowed to graze for 1 to 3 months, 40% were allowed more than 3 months of grazing. During this same period 21% were given vitamin supplements in addition to the pasture grass, and 27% of the horses were given minerals containing additional vitamins. Since there seems to be no risk of beta-carotene deficiency, the total amount of vitamin A supplied in the feed should be moderated to avoid any risk of toxic levels accumulating in the body. On the other hand, alpha-tocopherol supplements should be considered necessary for hard working horses, mares at long-term gestation, lactating mares as well as growing horses. According to the survey, the two most common reasons for using vitamin supplements were shedding of coat in spring, and change of coat in autumn. The survey also highlighted that horse owners experience confusion in determining the actual requirement...
