Influence of specific management practices on blood selenium, vitamin E, and beta-carotene concentrations in horses and risk of nutritional deficiency.

Suboptimal blood selenium and plasma alpha-tocopherol concentrations occurred in 16.7% and 35.5% of horses, respectively, despite most owners providing supplementation. Inadequate pasture access was associated with alpha-tocopherol deficiency, and reliance on selenium-containing salt blocks was associated with selenium deficiency.