Feeding for Happy Feet: A Recipe for Healthy Hooves

a halfcup to one full cup of ground flaxseed per day will provide sufficient omega3 fats for the average mature horse.
Minerals
Minerals are essential in the diet as they support every biochemical process in the body. Minerals are broken into two groups macrominerals which are fed in larger amounts and microminerals fed in smaller amounts. 
Calcium is a critical macromineral responsible for many processes including skeletal bone formation muscle contraction and relaxation and neural function. Calcium is also necessary to support the enzymatic reaction that produces the disulfide bonds which link the keratin proteins in the hoof. While it is important that your horse consume adequate calcium in terms of grams per day it is equally important that the calcium level be balanced with the phosphorus level. Calcium should be fed at higher levels than phosphorus at ratios of 21 up to 61. Diets in which phosphorus levels are higher than calcium can reduce calcium absorption which can lead to deficiencies. While calcium deficiencies can cause hoof abnormalities other symptoms such as bone fractures or tetany involuntary muscle cramping and spasm would probably be noted first. Generally sufficient calcium can be obtained from good hays with alfalfa hay being higher in calcium than grass varieties. Additional supplementation may be required if your horse is on a high grain diet grains are high in phosphorus and low in calcium or if your horse has higher requirements as do gestating or lactating mares. Calcium can be supplemented by way of commercial complete feeds or vitaminmineral blends
Copper and zinc are two microminerals often associated with healthy hooves. Zinc is necessary for healthy skin hair and hooves while copper increases hoof wall strength. Like calcium and phosphorus zinc and copper also need to be fed at the correct ratio to one another usually 31 or 41 in favour of zinc to prevent deficiencies.
Zinc and copper deficiencies have been noted in some regions of Western Canada. If you suspect that you are in an area that may have low soil levels a chemical analysis of your hay and pasture is a good idea. Zinc and copper are usually supplemented adequately in commercial feeds.
Selenium is necessary for the body to produce good healthy cells. It acts as an antioxidant and works together with Vitamin E to support the immune system. Large areas of Western Canadas soils are severely deficient in selenium. Thankfully most commercial feed companies supplement