Different workloads, stages of growth, pregnancy, and lactation require different dietary configurations for the horse. To meet those needs, horse owners often want to use supplements. However, you should realize that supplements could cause more problems than they solve, writes Dr. Joseph J. Bertone in the February edition of The Horse. Combining multiple supplements without consideration for your horse's forage might adversely affect important mineral balances. Take for example a pregnant mare fed alfalfa hay, which has a high calcium to phosphorous 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 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. Therefore, the first thing that should be done when you consider adding a supplement to any horse's diet is determine if one is needed. You should consult with your veterinarian or equine nutritionist on this issue. The second thing you need to realize is that supplements are not all good for your horse--and may even be harmful, as in the case of the pregnant mare above. The third thing is that not all advertisements are completely factual. In many cases, the supplements might provide no more nutrition than a quality grain. Many supplements are not quality controlled and might not contain what the labels claim they do. There are a great many supplements with various claims that have never been substantiated by quality research. The Internet is loaded with them. Reputable nutritionists have designed diets for pregnant mares, old horses, growing horses, etc. If you'd like to check out the adequacy of your horse's current diet before changing to one of these, you can ask a feed company to provide an analysis of your horse's hay (or information on hays from the area where it was grown, if available), and the company can identify a tailored supplement that complements the forage backbone of your horse's diet. "Regarding supplementation, I believe the industry is often naïve when developing new supplements for the equine market," said Dr. Joseph Pagan of Kentucky Equine Research in Versailles, Ky. "There may be a much broader physiological effect than we might expect when horses are fed things that they have not evolved to eat normally. A recent research study that Kentucky Equine Research conducted in conjunction with the Waltham Center for Pet Nutrition illustrates this point. "Using a stable isotope (radiation-emitting molecule), we have now determined that adding 10% vegetable oil to a grain meal doubles the length of time the meal is retained in the horse's stomach. Whether that is a good thing or a bad thing is debatable, but the point is that vegetable oil had a major impact on GI (gastrointestinal) motility that was not previously recognized. "We, as an industry, really need to conduct more research on new supplements before we throw them in a pail with a fancy label and send them off for horse owners to buy," Pagan concluded.