SCIENCE SUPLLEMENTS – How management of horses can result in deficiencies of essential dietary anti-oxidants


It is well recognised that deficiencies in the dietary anti-oxidants selenium and vitamin E can be associated with neuromuscular diseases, as well as having negative effects on fertility.

Selenium concentrations in soil can vary markedly, this will result in varying concentrations of selenium in both grass and forage. The natural source of vitamin E for the horse is lush green grass. Vitamin E cannot be made by the horse, and it is poorly preserved in hay or haylage. Therefore theoretically, horses with limited access to pasture could develop vitamin E deficiencies and, in areas of soil selenium deficiency, lack of dietary supplementation could result in selenium deficiency.

The objective of this study was to evaluate the effects of different owner management practices on the levels of selenium, vitamin E and beta-carotene (vitamin A precursor) circulating in their horse’s blood.

Samples from 331 horses were analysed for plasma selenium, vitamin E and beta-carotene concentrations. Owners gave details of daily selenium and vitamin E intake, pasture access, and exercise load.

Nearly 88% of the horses received supplemental selenium. Low or marginal blood selenium levels were seen in 17% of horses. Non-supplemented horses were twenty times more likely to have low blood selenium than supplemented horses.

Supplemental vitamin E was provided to 87% of horses. Low or marginal vitamin E levels were seen in 35% of horses. Access to green grass for more than 6hrs daily was strongly associated with adequate vitamin E concentrations. Where pasture access was limited, oral supplementation with >500IU/day of vitamin E was significantly (P < .001) associated with higher plasma vitamin E concentrations compared to horses with inadequate supplementation.


Suboptimal blood selenium and plasma vitamin E concentrations occurred in 17% and 35% of horses, respectively, despite most owners providing supplementation. This highlights the importance of paying attention to the amounts of vitamins and minerals provided in feed, and the amount of the feed you give your horse on a daily basis. Less than six hours of pasture turnout daily was associated with vitamin E deficiency, this is of particular significance at this time of year as pasture turnout begins to be restricted and the quality of pasture deteriorates. Vitamin E should be supplemented if your horse does not have access to goof quality pasture for more than six hours a day.

Read this paper for yourself: HERE

Pitel MO, McKenzie EC, Johns JL, Stuart RL. Influence of specific management practices on blood selenium, vitamin E, and beta-carotene concentrations in horses and risk of nutritional deficiency. J Vet Intern Med. 2020 Jul 20.

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