If your senior horse needs to put on a few, first determine the number of pounds using the standard body condition score system (review the process at bit.ly/conditionscore). Then, use that score to determine how much to increase his feed. For example, for every condition score below 5 (can’t see ribs but can easily feel them with your hand), a 1,100-pound horse needs to gain about 45 to 50 pounds. Each 1-pound gain requires about 8,000 to 9,000 kcals over the calories needed for maintenance.
So, if your horse needs to go from, say, a 4 to a 5, he needs to gain about 45 pounds, requiring a total of approximately 380,000 additional kcals. To add that amount safely over 90 days, you’d want him to gain about a half a pound a day. To achieve that, you’d increase his feed by about 4,500 kcals per day—which could be accomplished by adding about 2 pounds of alfalfa hay and 2 pounds of a commercial feed. (Build up to that change gradually to reduce the risks of digestive upsets; learn more at purinamills.com.)