When horses roamed the countryside, their diets didn’t require supplementation. As horses migrated, they fed on diverse species of plants in various soils and climatic environments. Different species of plants accumulate soil minerals differently based on their physiology, soil type, and climate, and this variety probably covered all of the horse’s dietary needs.

Today’s horse is exposed to a fairly uniform diet, with hay or pasture lacking in diversity. Hay or pasture (forage) is the backbone of this unvaried diet, and the purpose of dietary supplementation should be to complement the diet for different situations. Different workloads, stages of growth, pregnancy, and lactation require different dietary configurations. To meet these needs, horse owners often want to use supplements. However, you should realize that supplements can cause more problems than they solve.

Combining multiple supplements without consideration for the forage might adversely affect important mineral balances. Take for example a pregnant mare fed alfalfa hay, which has a high calcium to phosphorus ratio. The owner purchases a supplement purported to be essential for pregnant mares. Pregnant mare supplements often contain high calcium levels and unnecessary calories. The combination of the alfalfa hay and the supplements in this diet could increase the risk of inducing developmental orthopedic diseases in the foal such as osteochondrosis dissecans (OCD) or possibly angular limb deformities (crooked legs), as mineral imbalance can cause abnormal bone growth. Also, excess calories make mares obese, and they then seem to have more parturition and post-foaling problems.

This problem often is compounded as more supplements are added to the diet–for improving feet, battling Cushing’s disease, adding red blood cells, conditioning skin, improving appetite, etc