Vitamin E requirements of adult Standardbred horses evaluated by tissue depletion and repletion

Abstract

Summary Vitamin E requirements of adult Standardbred horses were evaluated by tissue depletion and repletion. All the horses used in the study were given the same basal feed low in vitamin E during the eight months of the experiment. After an initial depletion period of two‐and‐a‐half months the horses were divided into groups according to the amounts of DL α‐tocopheryl acetate given (0 mg, control; 200, 600, 1800 and 5400 mg, respectively) as a daily oral supplement. The supplement study was followed by a second depletion period. Total vitamin E content and individual natural tocopherol isomers and tocotrienol isomers were measured both in the feed (hay and oats) and in tissues (serum, liver, skeletal muscle and adipose tissue) using high performance liquid chromatography with fluorescent detection. Tissue vitamin E response to different dietary vitamin E levels were studied. The serum total lipid content remained unchanged during the experiment; serum vitamin E levels were expressed per gram serum lipid. The total vitamin E levels in serum, liver, skeletal muscle and fat reflected the supplement levels. The highest vitamin E levels were seen in fat tissue, followed by the liver and by skeletal muscle. In spite of the wide occurrence of the different vitamin E isomers in the feed, α‐tocopherol was almost the only isomer detected in the tissues. To ensure nutritional adequacy, 600 and 1800 mg of dl α‐tocopheryl acetate was suggested as an optimal oral daily supplement of vitamin E to adult Standardbred horses given feed low in vitamin E; this corresponds to 1.5 to 4.4 mg/kg bodyweight. In addition, it appeared preferable to give the supplement daily to maintain a constant level of vitamin E in the serum, liver and skeletal muscle, rather than occasionally to give higher doses.

Evaluation of the risk of motor neuron disease in horses fed a diet low in vitamin E and high in copper and iron

“…Adverse effects were not observed in horses consuming a diet containing < 15 U/kg of dry matter, but horses were fed the vitamin E-deficient diet for only 3 months in that study. 39 We believe that more prolonged feeding of vitamin E-deficient feeds increases the risk of EMND.…”

A Comparative Review of Vitamin E and Associated Equine Disorders

“…Baseline serum or plasma vitamin E concentrations vary widely among healthy horses as does the individual response to supplementation, especially at higher dosages . In humans, polymorphisms in many of the genes involved in vitamin E uptake, distribution, and metabolism can contribute to individual differences in response to vitamin E supplementation .…”

“…For that reason, it has been suggested that tissue α‐tocopherol concentrations could be a better marker of whole body α‐tocopherol status than plasma/serum concentrations. In healthy horses, plasma and adipose tissue concentrations and plasma and hepatic and muscle concentrations are linearly correlated. This correlation is also evident in deficient horses suffering from neuroaxonal dystrophy/equine degenerative myeloencephalopathy (NAD/EDM) (Finno CJ, unpublished data), but not in horses with vitamin E‐deficient myopathy .…”

“…Baseline reference ranges for tissue and CSF α‐tocopherol concentrations are provided in Table . Significant correlations between plasma/serum α‐tocopherol concentrations and adipose tissue, liver, muscle, and CSF occur in healthy horses. Muscle, nervous, and adipose tissue concentrations are the most stable and slowest to change upon dietary alteration .…”

“…Vitamin E deficiency, in and of itself, does not appear to reliably cause disease in horses. Studies examining the effect of vitamin E deficiencies in exercising or resting horses have revealed no apparent clinical signs resulting from vitamin E deficiency . There are, however, 3 specific diseases that consistently have been associated with α‐tocopherol deficiency: EMND, NAD/EDM, and vitamin E‐deficient myopathy.…”