Starch in grains, including oats, barley, wheat and corn, have been associated with induction of equine laminitis, foundering and lameness. Laminitis is generally exhibited by a loss and disorganization of the lamellar basement membrane, which causes detachment of the foot bones to the hoof capsule. Rotation and sinking of the boney column may lead to permanent crippling, and is the second leading cause of death in horses (severe lameness). In recent years scientists have reported the possible involvement in equine laminitis of carbohydrates such as sugars, starch and fructan, which are often present in grass forage. Horse owners sometimes overlook the possibility that forages may contain high concentrations of carbohydrates. Numerous factors are known to influence the amount of carbohydrate present in various plant parts. Plant carbohydrate content depends upon the species in question, stage of plant development, as well as environmental conditions during growth. Plant growth and carbohydrate content are influenced by many variables including root and shoot temperatures, light intensity, plant nutrient availability, and water status. In this study carbohydrate contents and forage quality of air dried (harvested) oat hay (forage) were measured on eight stages of growth (dates over the plant growth cycle) for early- and late-planted oats. In general, mature plants are higher in fiber and lower in carbohydrate content than young immature plants. However, we found that ambient temperatures during growth of oat hay often influenced forage carbohydrate content and other forage quality factors in addition to plant maturity. Thus, carbohydrates in mature oat hay in late fall when temperatures were cold and days were getting shorter were as high as those in immature oat hay. Detailed data from carbohydrate and forage quality analyses, over growing seasons and maturity stages, will be provided.