Vitamins and Minerals Explained

Which supplements are necessary, and when are you offering too much of a good thing?
by Wendy Harless Mollat, DVM, Diplomate ACVIM

As noted in last month's column, the bulk of your horse's diet should come from good quality forage (hay, hay pellets or hay-based complete feeds); however, the addition of certain supplements is often necessary to make up for vitamin and mineral deficits that may be present in certain types of feed or geographic regions. It is equally important to make sure you are not providing excessive amounts of certain vitamins and minerals, as this may lead to harmful toxicity. The vitamins, minerals and other supplements highlighted below are geared toward the adult horse (age 2-20 years). Broodmares, growing horses and high performance horses will all have varying needs that cannot specifically be addressed in this article.

Selenium
Selenium is a trace mineral present in plants. Our Northwest soil is notoriously deficient in selenium; therefore, forage grown here is also selenium deficient. To support normal immune system and muscle function horses need 1-3mg of selenium per day, with performance horses and broodmares having the highest requirement. Selenium deficiency can occur in any age horse and usually manifests as mild to severe muscle disease or difficulty chewing. On the other hand, selenium toxicity results in hair loss and hoof wall damage. Because the safety range for this trace mineral is so narrow, it is important not to over-supplement by feeding multiple products that contain selenium.

Vitamin E
Vitamin E is an important antioxidant that counteracts free radical-induced damage throughout the body. It is important for maintaining normal muscle and nerve function. Deficiencies are often associated with limited access to pasture or green forage or prolonged feed storage--this vitamin is very labile and degrades quickly in dried feeds. In general, horses require about 250-300 IU of Vitamin E daily. Supplementation with natural vitamin E (alpha tocopherol) versus synthetic sources is preferable, as the former is more readily absorbed and utilized in the horse.

Calcium and Phosphorous
Most horses on a forage-based diet have adequate intake of calcium and phosphorous, yet it remains important to pay attention to the ratio of these two minerals to each other. Imbalances can cause significant health problems. The ideal ratio is approximately 2:1 (calcium:phosphorous). Ratios of less than 1:1 decrease calcium absorption in the GI tract with serious consequences on skeletal development and repair. Ratios exceeding 3:1 should be avoided in growing horses. In general, hay is higher in calcium and grain is higher in phosphorous. Therefore, diets based largely on grain or bran sources have skewed ratios. With rice bran in particular, look for “stabilized” formulations in which the calcium content has been adjusted to avoid problems.

Joint Supplements
There are literally hundreds of supplements marketed for improving joint health. Glucosamine and chondroitin sulfate have been heavily promoted for the treatment of osteoarthritis and cartilage damage. All of these products are classified as neutraceuticals – over-the-counter nutritional supplements that may have health-promoting properties. Unlike prescription medications, the Food and Drug Administration (FDA) does not regulate neutraceuticals, so the manufacturer does not have to provide any scientific research to substantiate the claims made on the label. When choosing an oral joint supplement, the decision should be made based upon your veterinarian’s recommendation; individual experience and clinical response may vary for each horse.

Metabolic Supplements
Metabolic syndrome and Equine Cushings Disease are two health conditions that are receiving increased awareness by owners and veterinarians. While each condition has distinct differences, it is not uncommon for both groups of horses to develop insulin resistance. Under normal circumstances, insulin is responsible for helping shuttle glucose from the bloodstream into the cell, where it can be utilized as an energy source. The hallmark of treating insulin resistance is to increase exercise and control carbohydrate intake.

• Chromium – Research in other species has shown that chromium may improve insulin sensitivity. The jury is still out on the effectiveness of this supplement in horses, but there is no evidence that it is detrimental.

• Thyroxine – If your horse is overweight and has been diagnosed with Metabolic Syndrome or Equine Cushings Disease, your veterinarian may recommend treatment with a synthetic thyroid hormone to aid in weight reduction. It is important to note that these horses are not hypothyroid and that by administering a thyroid supplement the horse may temporarily become hyperthyroid. While studies have shown that this drug can speed weight loss and improve insulin sensitivity, long-term equine safety studies have not been performed. Since potential adverse side effects can occur, thyroid supplements are best used for the shortest time possible to achieve the desired effect.

This is simply an overview of some of the supplements you will encounter in the equine market. It is important to consult with your veterinarian to design a feed and supplement program that is most appropriate for your horse.