horses may appear normal within 3 months.15 It should be noted, however, that return to performance may result in deterioration.
(Hercules deficient photo) Same horse several years later who was kept on a dry lot without any vitamin E supplementation. He developed a vitamin E deficient myopathy with significant generalized muscle atrophy.
Same horse still kept on the dry lot but fed 5000 Units per day of water dispersible alpha tocopherol (Hercules after).
VITAMIN E SUPPLEMENTATION It is important to realize that the absorption and metabolism of vitamin E in healthy horses may differ from horses with vitamin E deficiency. Thus, the choice of the type of vitamin E supplement should differ depending upon whether a maintenance supplement is being selected for a horse with normal serum α-tocopherol or whether there is a need to rapidly increase serum α-tocopherol in a horse with low serum α-tocopherol and clinical signs of vitamin E deficiency. Vitamin E can be obtained from natural or synthetic sources, but the chemical structure of each is different. Natural vitamin E www.faep.net
is composed of one isomer (d-α-tocopherol [RRR-α-tocopherol]), and it is the most bioactive form in animal tissues. Synthetic vitamin E is a mixture of eight isomers (dl-α-tocopherol [all-rac-α-tocopherol]), of which only one is identical to the natural isomer. These eight isomers vary greatly in relative biopotency. Furthermore, when synthetic or natural vitamin E is formulated as a feed additive, it is manufactured as an esterifed form (α-tocopheryl acetate) to prolong shelf life. In order for α-tocopheryl acetate to be utilized in the body, the ester has to be removed and the α-tocopheryl made water-dispersible by the action of bile salts (micellization). These additional steps may limit α-tocopheryl acetate absorption in the horse. To account for differences in biopotency, the relative strengths of different forms of vitamin E are expressed as international units (IU) in which 1 mg of synthetic acetate equals 1 IU, 1 mg of natural acetate equals 1.36 IU, and 1 mg of natural alcohol equals 1.49 IU.16 These conversion factors were developed using laboratory animal models. A recent study in horses found that relative to synthetic (dl-α-tocopheryl acetate), natural-source vitamin E acetate (d-α-tocopheryl acetate) had 1.97 and naturalsource vitamin E alcohol (d-α-tocopherol) 2.52 times the potency of synthetic vitamin E.17 To further enhance the bioavailability of α-tocopherol, water dispersible formulations of vitamin E have been developed. When tested, two of the commercially available water dispersible natural vitamin E products had a bioavailability 5.59 (Elevate WS, Kentucky Performance Products LLC, Versailles, KY) and 6.13 (Nano•E, Kentucky Equine Research, Versailles, KY) fold higher than synthetic vitamin E acetate (d-α-tocopheryl acetate).17 The capacity of these compounds to significantly increase serum α-tocopherol concentration in horses has been studied in horses with normal baseline α-tocopherol. Synthetic forms of α-tocopherol produced no significant increase in serum over a range of doses each fed for 14 days. In contrast, the natural acetate form caused a significant increase when fed ≥ 2000 IU/500 kg horse for 14 days and the water dispersible formulation of natural α-tocopherol had a significant and greater increase in serum levels at ≥ 1000 IU/500 kg horse.18 It is important to realize when interpreting these studies that the absorption and metabolism of vitamin E in healthy horses may differ from horses with vitamin E deficiencies. In two studies using horses with a marginal/deficient α-tocopherol status but no clinical signs of deficiency, a serum α-tocopherol concentrations increased with both all-rac-α-tocopheryl acetate (synthetic) and water-dispersible RRR-α-tocopherol (natural; Emcelle, Steward Prodcuts, Bedford, TX) at 10,000 IU/500kg horse/day for 10-14 days, with levels being twice as high in the group on RRR-α-tocopherol. Cerebrospinal fluid concentrations of α-tocopherol increased from baseline (1.3 to 3.5 fold) only in horses supplemented with natural water dispersed RRR α-tocopherol.4 Vitamin E deficiency: Natural-source water-dispersible forms of vitamin E at 10 IU/kg body weight seem like the obvious choice for optimal treatment as they are 5-6 times more bioavailable than synthetic vitamin E acetate, and a 5000-IU dose/horse more than doubles serum vitamin E levels within 12 hr.17 Before implementing supplementation it is important to measure The Practitioner 9