If you spend much time looking at horse magazines odds are you have seen an ad or two for a horse supplement. The real question is does your horse need a supplement? My best advice on feeding supplements and if your horse needs a supplement would be to ask your vet. Your veterinarian should be able to tell you what studies have found about different supplements and more importantly if your horse even needs to be supplemented at all. Like grain horses in more strenuous training are going to need better nutrition than a horse that gets ridden every now and then. Your vet can let you know about what kind of supplements are out there and would be a pretty good unbiased(hopefully) opinion on what brand or what kind of supplement would work best for your horse.