Vitamin A Deficiency in Horses

It has been a long wet winter and many of our horses have been unable to be turned out for several months.  Some of these horses have now been diagnosed with Vitamin A deficiency, so why has this happened and how can it be prevented next winter.

In addition, some horses now have the potential to develop Vitamin A deficiency as they will now be on restricted grazing due to health issues such as being a good-doer, Equine Metabolic Syndrome and having the potential to get laminitis.

I have put together a Vitamin A fact sheet which I hope you will find useful:

Why do horses need vitamins such as Vitamin A?

Vitamins are organic compounds that are vital to a wide variety of biochemical processes in your horse’s body.  They can be divided into two categories: fat soluble (vitamins A, D, E, and K) and water soluble (B vitamins and vitamin C). Fat soluble vitamins are more readily stored in the body (and thus are more likely to build up toxic levels when present in excessive amounts), while any excess of water soluble vitamins is excreted fairly promptly if it remains unused by the body.

Vitamins can also be classified by their source.  Vitamins C, D, and niacin (one of the B vitamins) are all manufactured by the horse’s body from other organic compounds it has ingested. The other B vitamins and vitamin K are produced by the beneficial microbial organisms living in the horse’s caecum and large intestine. Vitamins A and E are the sole vitamins not produced within the horse’s body, and therefore must be supplied in the horse’s diet.

What does Vitamin A do in the horse?

Vitamin A is thought to be crucial for good vision and vitamin A also plays a role in bone and muscle growth, reproduction, and healthy skin.

The main precursor for Vitamin A, beta-carotene, is present in fresh pasture and good quality hay in levels that are more than sufficient to satisfy the horse’s requirement. Vitamin A will be stored in the liver for up to six months, to be released as needed by the horse’s body.

How does a horse become Vitamin A Deficient?

Vitamin A deficiency may develop when a horse’s diet is devoid of good quality green forage (not uncommon in the winter when pasture is unavailable and hay quality is often poor) for longer than six months. Vitamins reduce in hay with age and if it has to be soaked.

As most of us know, some horses will have been off grass for nearly six months over the winter and if they had been on restricted grazing prior to that, they may well have used up all their stores and become deficient.  A deficiency may still develop if they have to have restricted grazing now the spring grass has arrived.

Symptoms of deficiency include night blindness, tearing of the eyes, bone and muscle growth defects, a dull coat, reproductive problems, and increased susceptibility to disease and infection.

What happens if I give my horse too much Vitamin A?

Typically, Vitamin A toxicity (too much), only occurs as a result of over-supplementation in the diet. Mild toxicity can cause stunted growth and poor skin condition, while a more severe toxicity may result in depression, weight loss, hair loss (alopecia), neurological dysfunction, serious bone deformities, and death.

How can I make sure that my horse gets the right amount of Vitamin A without weight gain or fizz?

The simplest way is to feed the manufacturer’s recommended daily amount of a good quality balancer or vitamin and mineral supplement all year round.  Most reputable feed companies produce a low calorie, low sugar and starch version of these so there is no excuse not to feed one to your horse.  Of course, these will make sure that your horse has the correct amount of all vitamins and minerals to ensure optimal health including a strong immune system, digestive system, healthy skin, hair and hooves etc.

Feeding a small amount of a cube or mix will not contain sufficient Vitamin A but a balancer fed at the advised rate will. However, if you are feeding a concentrate feed, check the amount of Vitamin A it delivers as you may need to supplement it if the horse is not having sufficient of it to ensure optimal Vitamin A levels.