MEDICAL ARCHIVES
08.02.2006
Vitamin A - What are its strong points?
Vitamin A, or retinol, is involved in metabolic processes, blood cell formation, health of skin and lining cells of the gut and breeding tract, as well as vision, and importantly in racing and working horses, tendon strength - a strong point. Let's discuss this specifically.
Facts and Stats
- Horses can obtain vitamin A from carotene precursor compounds in green plants, predominantly P-carotene, and supplements containing preformed vitamin A (retinol). Vitamin A (and vitamin E) has to be obtained from the diet - it cannot by synthesised in the horse's body.
- Vitamin A can be stored in reserve by the liver for up to 2 months to meet normal daily needs - an obvious adaptation to overcome low vitamin A intake when pastures dry off and 3-carotene levels decrease. The uptake and conversion of P-carotene to vitamin A in the gut lining cells is regulated by the liver storage of retinol which decreases as a horse progresses in training.
- Carotene in hay is destroyed by sun curing and long term storage, with 50% loss over 6-7 months. Under hot humid conditions, losses of 80% of P-carotene activity have been reported in lucerne hay after 3 months of storage.
- As green plants mature, P-carotene activity decreases by 50% from early to full bloom.
Studies in the United Kingdom, reported by Dr. Abrams and co-workers in 1979, found that the incidence of tendon strain injuries in racing horses decreased dramatically over a 6 month period when their diet of oats and grass hay, which had been low in P-carotene activity, was supplemented daily with 50,000iu of retinol (preformed vitamin A). Racing performance was also improved by the vitamin A supplement!
Other studies suggest that all horses in training have a higher risk of respiratory infection when fed on a diet deficient in vitamin A to meet their needs.
So what's the practical benefit?
There are two main benefits from feeding a supplement mixed into a feed, or a prepared feed containing from 40,000-50,000iu vitamin A each day.
- Tendon strength may be enhanced, as well as resistance to respiratory infection.
- Horses recovering from tendon injuries may have a better chance of regaining optimum tendon strength when given a supplement containing 50,000iu of retinol daily.
- Race and athletic performance may be improved.
Always remember to store the vitamin A supplement or feed in a sealed, airtight container and use it before the expiry date.