While many of us believe our "complete" feed gives our horses all of the essential minerals he needs for optimum health, that may not, actually, be true.
Due to variations in how much owners feed each horse, your horse may not be getting the recommended daily amount.
Horses need calcium, phosphorus, magnesium, potassium, sodium and sulfur. They also need some "trace" minerals-smaller amounts of other minerals:
Some minerals are more prevalent in some parts of the country than in others. So while you may think your horse is getting proper nutrition from locally grown hay, he may not be.
Putting out a high quality mineral block is the first and most important step. But you may need to add even more minerals to his diet. Look for a dietary supplement that matches the particular needs of your horses. Veterinarians recommend that you don't overlap-use only one supplement and do so in moderation.
Mineral overdoses can happen, so definitely compare labels and check with your veterinarian before feeding any supplements.