[header] How to give your horse the right supplements [title] Collect a sample of the hay you feed your horse. [step] Most horses eat a combination of roughage, or hay, and concentrates, or grain products. Usually, nutritional content will be listed on the grain feed label, so you'll only need to collect a sample of your hay to be tested. 
[title] Contact an agricultural research laboratory to have your hay tested. [step] Agricultural research laboratories offer hay testing that will provide you information about the crude protein content, fiber, and vitamins and minerals in your feed.