Technical Abstract: Several equine illnesses, including laminitis, equine polysaccharide storage myopathy, and equine metabolic syndrom, have been associated with high levels of sugars or other carbohydrates in horse diets. Unfortunately, many of those involved in the treatment of these diseases do not realize that forages, not just feed grains, present important feed/carbohydrate issues. It is important that horse owners and equine care givers know the forage quality factors of horse feed and that they are informed about the variables known to affect carbohydrate levels in both hay and grazed forages. Factors that influence carbohydrate levels in feed include plant species, stage of growth, and the environmental conditions at the time of harvest. Cool temperatures, during spring and fall when conditions are otherwise favorable for plant growth, are often associated with increased carbohydrate levels in plant tissues. In general, forage carbohydrate levels tend to be lower during the summer when temperatures are warm, early in the day before photosynthesis has resulted in a carbohydrate buildup, in more mature foliage, and in warm season (C-4) grasses. The only way to be sure of the carbohydrate level in a forage or hay is to have a forage analysis done by a reputable laboratory.