Foal growth and development starts even before birth so proper nutrition of the mare is critical. Dr. Karen Davison from Purina Feed indicates foals are eating machines from birth and will nurse 70 or more times per day while consuming 30 pounds of milk per day during the first months of life. And this is a good thing because initially the mare's milk is the best feed for the foal, but mare's milk does decrease in nutrient content after the first month of lactation.
After the first month, Dr. Davison believes foals require some supplementation for adequate nutrition and growth as foals who only have mare's milk after the first month will grow at a reduced rate. The ideal foal feed would consist of high quality and very digestible concentrated nutrition, as young foals can only eat a small amount at a time. A recommendation is to give a pound of dry foal feed per day per month of age, so a 2-month-old foal would be fed 2 pounds per day and a 3-month-old foal would be fed 3 pounds per day, assuming you are dealing with a normal, adult-size horse breed. Free choice creep feed is not a good idea because foals can become overweight. One concern with abnormal feeding is the possibility that the foal will develop an orthopedic disease. Many times foals are allowed to eat alongside with the mare and consume a ration balanced for the mare but not the foal. These foals do not grow as rapidly when nursing the mare and then when weaned are introduced to a ration for maximum growth. When on the new ration, the body will try to catch up and contracted tendons and other conditions can develop, so foals should be fed balanced rations from birth.