Physiology of vitamin E in maintenance and exercising horses as measured via blood and adipose tissue concentrations

Abstract

Vitamin (Vit) E concentrations are often monitored in horses as a health-screening tool and to determine supplementation. There is an established reference range for serum values, and commercial feeds and supplements can provide additional Vit E to the diet in several forms. However, the physiology of Vit E in horses is poorly studied, especially considering it is a fat-soluble vitamin. This pilot study was designed to record Vit E levels in horses from both blood and adipose tissue before, during (blood only), and after a 6-week exercise program, and to test the hypothesis that these concentrations may differ based on Vit E dietary source and training. Horses at the Purina Animal Nutrition Center (n = 12, 9 Quarter Horses and 3 Thoroughbreds, mean BW 518 ± 15 kg) were split into 3 equal groups: control (CON), exercise (EX), and pasture (PAST). All horses received 1.8 kg of Purina® Strategy®/day (334.9 IU/kg Vit E DM). CON and EX received 2.0% BW grass hay daily (1.6 IU/kg Vit E DM), and were group-housed in dry lots. PAST received no hay and were grouped outside on pasture (5.1 IU/kg Vit E DM). Vit E intake exceeded NRC requirements for CON and PAST but was below NRC for EX due to study design, to ensure equal Vit E intake in dry lot groups. All horses had adequate Vit E intake and status before the trial. EX received a 6-week exercise program on an Equi-ciser, 3 d/week, progressing to 48 min/d of walking and trotting. Blood samples were obtained for 9 wk via jugular venipuncture for serum Vit E status. Tailhead adipose samples were obtained via aseptic biopsy technique under the use of local anesthetic and sedation, and immediately frozen in liquid nitrogen, the weeks before and after the exercise training period. All samples were evaluated for total tocopherols via HPLC (MSU VDL, East Lansing, MI). Data were analyzed using GLIMMIX ANOVA with repeated measures (SAS 9.4), for differences due to treatment, time and interactions with significance set at P < 0.05. There were no differences in serum Vit E levels between treatments or at any time points (P > 0.05, Vit E 8.6 ± 0.18 µg/mL, mean ± SEM). Adipose Vit E was not different between treatment groups (P > 0.05); however, levels significantly increased in all groups over time (P = 0.003, from 5.86 ± 1.09 to 18.16 ± 3.32 µg/mL, mean ± SEM). Overall, horses in this study had sufficient serum Vit E status throughout the trial, and an increase in Vit E concentrations in adipose tissue over time. Due to the small number of horses, this research should be repeated with a larger subset of horses with more adipose sampling times to get additional clarity on equine Vit E physiology.