A thin horse that struggles to gain weight may be classified as a hard keeper due to various factors affecting its metabolism and dietary needs. Metabolism plays a crucial role in determining whether a horse is an easy or hard keeper, with significant variations among individual horses and breeds. Thoroughbreds, for example, generally have faster metabolisms and may require more food to maintain body condition compared to draft horses. Additionally, temperament can influence metabolic rate, with nervous horses potentially needing more calories to maintain weight than calmer counterparts.

To address weight gain in a thin horse, adjustments to the feeding program can be made by focusing on increasing the caloric density of the diet. Three key nutrients that can help boost caloric content are fiber, starch, and fat. Fiber is a vital energy source for horses and can be found in grass, hay, and alternative sources like beet pulp or soy hulls. High-quality fiber from sources like alfalfa hay can provide essential energy for weight gain.

Starch, primarily found in grains, is another energy-dense option but should be fed cautiously to prevent digestive issues. Different grains have varying levels of digestibility, with oats being easier to digest compared to corn or barley. Proper processing of grains like steam rolling or cooking can enhance their digestibility for horses.

Fat is an excellent energy source that can aid in weight gain without causing excessive excitability in horses. Vegetable fats (oils) are generally more digestible and palatable than animal fats. Common fat sources include corn oil, rice bran, linseed, sunflower seeds, and soybeans. Adding fat to the diet not only provides concentrated energy but also contributes to improved coat condition and endurance in performance horses.

In conclusion, addressing a thin horse's weight gain involves understanding its metabolism, providing a balanced diet rich in essential nutrients like fiber, starch, and fat, and making gradual adjustments to the feeding program to promote healthy weight gain