Formulating Equine Diets

The most important component of a horse’s diet is forage, whether through hay, pasture, or a combination. The equine digestive tract is designed to deal with large amounts of forage; the microbial population is present to deal with the digestion of fiber; and the shape of the intestines (twists and turns) maximizes microbial fermentation, digestion, and absorption of nutrients. While the digestive tract is well suited to a life of grazing, it does not do well when horses are fed little hay or large concentrate (grain) meals. Therefore, it is extremely important that horse owners work toward maximizing the amount of forages in their horse’s diet. If a horse doesn’t consume enough true forage (for example if it has bad teeth and can’t chew hay very well), other high-fiber feeds such as beet pulp may be fed.

A rule of thumb is that a horse should consume at least 1% of its body weight as (dry matter) forage daily. So, a 500 kg horse should consume at least 5 kg (about 12 lbs) of forage each day. Ideally, horses will be offered more than that (closer to 1.5–2.5% of their body weight, depending on the horse). Any concentrate offered (if required) should be fed at 0–1% of the body weight, and should never be fed in amounts exceeding the forage (except in growing horses whose digestive tracts aren’t fully developed or suited for forages). Most horses will consume a total of 1.5–3% of their body weight per day, with the upper amounts being fed to lactating mares or horses in heavy work.

Most horse owners under-appreciate how nutritious forages are for their horses. The 5 kg of hay (even if it were the straight timothy hay described earlier) consumed daily by a 500 kg horse would provide 9.95 Mcal of energy, 485 grams of protein, 24 grams of calcium, and 11.5 grams of phosphorus. The requirements of this same horse (at maintenance) are only 16.65 Mcal of digestible energy, 630 grams of protein, 20 grams of calcium, and 14 grams of phosphorus. If the hay were offered at 2% of the horse’s body weight, its energy, protein, calcium, and phosphorus intake would be in excess.
 
Source: TheHorse