There are a couple of reasons why your horse may be losing weight in his topline. The most common is if he is an older horse. Many older horses will start to lose the topline quality regardless of exercise. However, in order to help prevent this from occurring, keeping the animal physically fit is best. Higher fat diets may also help keep the topline, but this will not work in every case in the older animal. You can try adding 1 to 2 lb of rice bran to the daily ration. Many people will tell you that protein is the problem; however, this is not the case. Most older horses will not need high protein to maintain condition, just a good-quality protein source and the addition of a fat source.