The foal’s first meal is colostrum or first milk, and this first milk contains antibodies that help the foal fight off infection during its early life. Colostrum can be absorbed for up to 24 hours but the absorption rate is not equal as absorption the first 6 hours is much greater than the absorption the last 12 hours. The foal’s digestive tract changes rapidly during the first 2 weeks of life.
Although the foal may nibble on grass at an early age, until about 2 months of age, the majority of nutrition comes from milk because the digestive tract is only able to handle milk. After 2 months of age, research from Kentucky Equine indicates the foal’s hindgut begins a period of maturation that lasts until about 6 months of age. The hindgut is populated by bacteria that the foal has ingested when nursing on the mare’s udder and by eating manure of the other horses. These bacteria colonize the hindgut and are necessary for hindgut fermentation to occur, which allows the older foal to utilize forage for nutrients. Of course, foals can also pick up infectious bacteria during this time that can lead to digestive tract and respiratory tract disease. One of the most common syndromes noted in almost all foals is foal heat diarrhea. Although it occurs at about the time the mare comes into her first heat after foaling, the mare’s foal heat really has nothing to do with the condition. Foal heat diarrhea is now believed to be due to microbial changes in the hindgut when the foal is about 10 days of age.