Carlson College of Veterinary Medicine

BACKGROUND: Selenium or alpha-tocopherol deficiency can cause neuromuscular disease. Beta-carotene has limited documentation in horses.

OBJECTIVE: To evaluate the effect of owner practices on plasma beta-carotene concentration and risk of selenium and alpha-tocopherol deficiencies.

ANIMALS: Three-hundred and forty-nine adult (≥1 year), university and privately owned horses and mules.

METHODS: Cross-sectional study. Whole blood selenium, plasma alpha-tocopherol, and plasma beta-carotene concentrations were measured once. Estimates of daily selenium and vitamin E intake, pasture access, and exercise load were determined by owner questionnaire. Data were analyzed using t tests, Mann-Whitney tests, parametric or nonparametric analysis of variance (ANOVA), Kruskal-Wallis test, Spearman's correlation and contingency tables (P < .05).

RESULTS: Nearly 88% of the horses received supplemental selenium; 71.3% received ≥1 mg/d. Low blood selenium concentration (<80 ng/mL) was identified in 3.3% of horses, and 13.6% had marginal concentrations (80-159 ng/mL). Non-supplemented horses were much more likely to have low blood selenium (odds ratio [OR], 20.2; 95% confidence interval [CI], 9.26-42.7; P < .001). Supplemental vitamin E was provided to 87.3% of horses; 57.7% received ≥500 IU/d. Deficient (<1.5 μg/mL) and marginal (1.5-2.0 μg/mL) plasma (alpha-tocopherol) occurred in 15.4% and 19.9% of horses, respectively. Pasture access (>6 h/d) and daily provision of ≥500 IU of vitamin E was associated (P < .001) with higher plasma alpha-tocopherol concentrations. Plasma beta-carotene concentration was higher in horses with pasture access (0.26 ± 0.43 versus 0.12 ± 0.13 μg/mL, P = .003).

CONCLUSIONS AND CLINICAL IMPORTANCE: 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.