First, you need to analyze your horse's diet. What kind of feed, how much, and how often? What kind of hay, how much, and how often? Any salt or mineral blocks? How much is your horse worked? Turnout? Etc.
You may need a good vit/min supplement, or you could just need a little something extra. It really depends on your horse's diet.
My horses get no grain or feed. They get free choice grass hay and alfalfa pellets. With the pellets they get an all in one vitamin/mineral supplement, 1/4-1/2 cup of ground flax, and 1/2 cup of apple cider vinegar. This is a simple diet that gives them great feet, coat, hair growth, and overall health.
I use a custom blend vit/min from Uckele Equine Nutrition. There are a few off the shelf products you can buy as well. My two favorite are HorseTech.com's High Point
and Grand Vite
. Uckele has one called Equi-Base Grass
. SmartPak has their SmartVite line
If you give your horse a fortified feed at the recommended levels (on the side of the bag) then you do not necessarily need an overall vit/min supplement. In that case, I would suggest something like Horsetech.con's Glanzen 3
, Grand Coat
, Source Focus HF
, Omega Hoof
, or EquiOmega