Horses tend to come in after the winter months carrying less condition especially if they've been living out. Luckily, once they are back in work and being fed good quality hay and hard feed, they soon start to put it back on. However, if you compete then you should get too complacent about things because although the majority of commercially produced horse feeds are specifically formulated to include all the minerals, vitamins and other nutrients a horse needs to remain healthy, there are times when a they may be deficient in certain of them.
When fed good quality hay and hard feed horses can appear to be in good all-round health, but when it comes to specific nutrients it can be hard to detect whether the ratio is correct which is particularly true where calcium and phosphorus intakes are concerned. An incorrect balance can result in horses going lame which is often put down to some sort of trauma to a front leg or even over-exercise when in fact, the lameness is being caused by a nutrient deficiency.
Performances horses and those in hard work are more at risk of developing some sort of nutrient deficiency, but mares in foal and lactating mares are also more at risk of being deficient in certain nutrients because they are being put under pressure to feed their foals too. Horses that are still growing and typically up to age of two are considered to be more at risk as well as horses that are standing in and being fed a hay-only diet without being given access to turnout are also more at risk of developing a nutrient deficiency.
According to studies carried out by the KER University in the States, many horses fed a hay-only diet tend to be deficient in Vitamin E which can leave them more vulnerable to infections simply because Vitamin E is a powerful antioxidant that helps maintain a strong immune system. It also maintains the respiratory tract and enhances absorption of Vitamin A so it's able to be stored in the body. The best and most natural source of Vitamin E is contained in grass and to a lesser extent in good quality hay.
However, a deficiency can have disastrous results causing two equine disorders which are equine motor neuron disease and equine degenerative myoencephalopathy with the latter being the rarer of the two diseases. However, the only way of testing whether any forage you are feeding your horse contains enough Vitamin E is to have it tested and if you find it is deficient you would need to add a vitamin E supplement to your horse's diet after having discussed things with your vet.
With this said, it's important to bear in mind that horses tend to absorb the natural form of vitamin E much more so than they do its synthetic form. When purchasing a supplement it's important that it contains the natural form of the vitamin which is d-α tocopherol – the synthetic form of vitamin E is dl-α tocopherol.
Young horses need Vitamin A because it is essential for their vision and for normal muscle and bone growth. It is also important for healthy skin and to maintain a strong immune response to any sort of infection. Vitamin A is also essential for reproduction and although horses do usually get enough of it from eating good quality grass, they get less from hay because the levels decrease once the grass has been cut.
All too often when a horse is put on a hay-only diet, their intake of Vitamin A is lacking and this particular vitamin is not added to commercially produced horse feed either. In short, horses tend to ingest enough of the vitamin when they are allowed out to grass, but if they don’t get to graze they could be deficient.
Vitamin C boasts valuable antioxidant properties and these help maintain and boost a horse's immune system. Horses do produce the vitamin naturally in their bodies, but when they are put under any sort of long-term stress they often don't produce enough with a typical example being when a foal is being weaned.
When a horse is ill or stressed, they tend to go off their food and this may cause a deficiency in Vitamin B. Horses produce this vitamin in their large intestine and it is essential for maintaining good skin and muscle tone as well as to promote healthy cell growth and division. On top of this vitamin B helps maintain both the nervous and immune system.
When horses go off their food it causes their hind-gut to be off balance and as such they don't produce enough vitamin B. Commercially produced horse feeds contain good levels of the vitamin so as long as you can get a horse eating again, they should not develop a deficiency.
Should a horse's diet be deficient in salt, it can cause metabolic problems and it's important to bear in mind that forage contains low levels of it. Commercially produced feeds only add a small percentage to their mixes so a deficiency often occurs especially in the working horse.
With this said, it's more a question of an “imbalance” rather than a deficiency which is especially true when it comes to calcium and phosphorus. Adult horses need a ratio of 1-1 whereas young horses need a ratio of 2-1. An incorrect balance can lead to horses developing problems with bone growth and issues like osteochondritis dissecans to name but one.
If you think your horse may be deficient in certain nutrients you need to discuss your concerns with the vet who would be able to take some tests to establish whether you are right or not. If it is found they are, then you may need to add the necessary supplements to your horse's feed or to change their diet so they are getting enough of what is missing. However, any changes would need to be done gradually to avoid upsetting your horse's delicate system and always under the guidance of a vet or equine nutritionist.