Horses have evolved to eat a very high fibre diet so this should be the main component of any feeding regime. Any extra nutrients or higher energy feeds the horse may need can be added by supplementary feeding if the hay or grass is deficient or the horse is working hard/producing a foal etc.
Horses require feed that takes a long time to collect and chew – slow feeding. They evolved to eat low energy (low calorie) fibrous food for many hours of the day and night. They have not evolved to eat ‘meals’ as we do. If you do not take this fact into consideration when feeding your horse you risk behavioural problems (such as ‘cribbing’) and gastrointestinal problems (such as colic/gastric ulcers/laminitis – laminitis starts in the gut and results in a serious problem of the feet).
Horses are herbivores. This means that they eat only plants. Plant matter is far bulkier than the feed of a carnivore (meat eater). Meat is also much more energy dense. This is why a dog spends a very small amount of time eating and large periods of each day sleeping compared to a horse that spends large periods of each day eating (or should do) and much less time sleeping.
Think of the horse as a fibre processing machine! We need to remember this when feeding them. As mentioned before horses have evolved to eat and process large volumes of relatively low quality (low calorie) grasses and other plants. Therefore we have to try to mimic the natural feeding behaviour of horses as much as is practical. Put simply it is much better for the horse to eat lots of low calorie food than a little high calorie food. Remember that what your horse likes best is not necessarily what is best for him or her! Just like a child will often choose sweets and chocolate over salad and vegetables, most horses will choose high sugar (high calorie) feed if given the chance!
Unless the horse is working hard (i.e. endurance, eventing, racing etc.) they can easily get too fat. This may lead to an owner reducing the quantity of feed when in fact it would be better to reduce the calories fed to the horse but keep up the volume. Reducing the quantity of feed fed to a horse can be dangerous as horses are meant to graze and browse for at least twelve hours a day. The saliva that a horse produces from chewing buffers acid in the gut which is dripped in to the stomach constantly and their gut is designed to work continually.
Whenever possible allow your horse to graze and aim for this to be the bulk of your horse’s diet. Well managed pasture with a diversity of species, is the best feed for horses and will save you money because you then do not have to buy as much (or any) supplementary feed. If your grass is high calorie (grass varies enormously in calorie content) and your horse tends to get fat you will need to be careful that he/she does not get overweight.
If there is not enough pasture aim to feed lots of hay. If you have a horse that is prone to getting fat try to source low calorie hay. If you buy your hay from a produce store ask them to source some for you. Even if they do not have any in they may find some if there is enough demand for it. If you are feeding hay that you think is high in calories you can soak it in water (in a haynet for about an hour) before feeding as this will leach out some of the sugar. Do not give the water used to soak the hay to your horse as this will now be high in sugar!
If you do decide to start feeding your horse concentrates (because he/she is working very hard and is not maintaining condition on hay/grass alone) then get some expert advice about what to feed. An independent equine nutritionist is a good place to start and reputable feed companies usually offer a free advice service. Aim to keep it as simple as possible – it is not a good idea to start feeding a variety of feed types as you can end up feeding the horse a very unbalanced diet indeed.
For more information please see: https://www.equiculture.net/responsiblehorsecare