A survey by the USDA indicated that 69% of responding horse owners add supplements to their horses’ diets. This could range from vitamin/mineral supplements to joint supplements to “performance enhancing” supplements. There are so many supplements available - How do you determine if you need to supplement the horse’s base diet and if so, what to supplement and how much?
In one catalog, over 90 dietary supplements are available for the horse owner to purchase. Advertising for these supplements contain claims such as “will increase power”, “build muscle”, “ensure maximum utilization of all protein sources”, etc. At some point in the decision process as to whether a supplement should be used, the horse owner should evaluate the validity of such claims. According to Ray Geor, BVSc, Ph.D., there are several questions to consider carefully when sorting through the information available on the efficacy of a given supplement. First, is there a scientific rationale that the use of the supplement could actually produce the purported effect? For instance, the addition of a nutrient that is critical to a metabolic reaction could theoretically improve the efficiency of that reaction. On the other hand, adding a supplement that has no scientific rationale for efficacy is usually a waste. For instance, there is no known function in the body for bee pollen, so there is no real scientific rationale for its addition to a horse’s diet.
If there is a sound scientific rationale for the use of a nutritional supplement, the next question to ask is “Is there evidence that the substance is absorbed from the digestive tract, and if so, does that substance reach the target organ or tissue where it could be of benefit?” For instance, if the substance is supposed to aid in joint health, but is not absorbed from the digestive tract, or is absorbed but does not reach the joints, it would be of little benefit to the horse.
Finally, the most important question is: “Is there evidence that the supplement works?” Even if a supplement is proven to be absorbed from the horse’s digestive tract and transported through the body, if there is no evidence that the supplement provides any improvement or benefit to the horse’s performance or health, then is there truly justification for using the supplement? Unfortunately, in horses there is little research on the effects of supplements on the performance of horses, especially when the control horses in the studies are fed balanced diets that meet all nutritional requirements. There are certainly many studies available that prove that adding a nutrient to a diet that is nutritionally deficient will improve performance and/or health.
There are many categories of equine dietary supplements, including joint supplements, digestive aids, relaxing supplements, performance boosting supplements, and many more. For the purpose of this discussion, we will focus only on nutritional supplements.
When it comes to nutrition, sometimes more is better, sometimes more is worse and sometimes more is just more. There are certain amounts of all nutrients that the body requires for optimum function and performance. If the diet is deficient in a nutrient, health and performance will suffer. If that nutrient is added to the diet, performance will continue to improve until the nutrient requirement is met. If more of the nutrient is then added, performance will plateau. However, there comes a point at which the continued addition of that nutrient will actually begin to hinder health and performance, and in some cases, continued over-supplementation can become toxic to the horse. For example, addition of vitamin A to a horse’s diet that is deficient in that vitamin will be of great benefit to the animal, relieving symptoms of night blindness, possibly anorexia, poor growth, etc. However, prolonged feeding of excess vitamin A may result in bone fragility, loss of hair and epidermis, and other symptoms. Supplementation of selenium to the ration is often recommended due to its role as an antioxidant, and is certainly beneficial to the animal with insufficient selenium in its diet. On the other hand, excess selenium can cause blind staggers – characterized by apparent blindness, colic, diarrhea, increased heart and respiration rates and lethargy.
One problem for horse owners is that they often don’t know whether the horse’s feeding program is nutritionally balanced and meeting all requirements or not. They may buy different supplements to address issues like hair coat, hoof quality, soundness and other issues, often supplementing with multiple products. Many of these supplements will contain several of the same ingredients or nutrients so when two or three different supplements are added together, even to address different issues, the result may be an overabundance of some nutrients.
Conversely, in some situations the horse owner feels that the ration is nutritionally balanced and complete because the horse looks good and is carrying adequate weight, but in reality the diet is deficient in several nutrients. In the short term, the deficiencies may not show obvious symptoms, but over time the results can be devastating and irreversible.
In general, the best option is to provide a diet that contains all the essential nutrients in the correct concentrations and balances. There are recommendations for feeding horses with specific conditions, such as equine polysaccharide storage myopathy or recurrent exhertional rhabdomyolysis, in which a supplement containing one or a few specific nutrients is specified. However, the first step in managing most, if not all conditions in horses is to ensure that the animal’s basic nutrient requirements are met.
Sometimes it is difficult to determine if a horse’s diet is meeting all the nutrient requirements without a complete ration analysis. Horses can appear to be in good health and body condition, when in reality some nutrients are deficient. A factor which plays a large role in such situations is the forage portion of the horse’s ration. Unless the forage is sampled and analyzed, it is impossible to determine the total nutritional status of the diet. In many cases, sending samples for analysis is not feasible due to economic constraints or even just practicality – i.e. if hay is purchased in large quantities it may be reasonable to sample and analyze, but it is not practical to analyze hay that is purchased in many small batches.
Further, horse owners often assume that horses that maintain their weight and body condition on pasture and/or hay alone are meeting their nutrient requirements. Looking at many hay sample analyses, one can see that this is often not the case. For instance, copper and zinc concentrations in forages are usually marginal or deficient for adult horses today. In a survey of hay samples from around the US conducted at the LongView Animal Nutrition Center, only one of six samples of hay contained adequate (yet marginal) copper to meet a horse’s nutritional needs, and no samples contained adequate zinc. These observations are borne out by the Feed Composition Library available at the Dairy One website (www.dairyone.com/Forage/FeedComp/). Out of 11,184 samples of grass hay, the average copper concentration was 9.3 ppm, and the average zinc concentration was 23.5. For 21,000 samples of legume hays, the average copper content was 9.2 ppm and zinc was 31.1. Again, considering that the 1989 NRC determines the minimum copper requirement for horses to be 10 ppm and zinc requirement 40 ppm, one can see that few hay sources meet even the minimum copper and zinc requirements for horses. Further, the contribution of amino acids to the diet from hay is often less than expected due to the variation of digestibility of forages in the upper digestive tract. In one study, only 2% of the protein in low/average quality alfalfa was digested in the upper tract (yielding amino acids). The remainder of the protein was digested in the hindgut, thus the amino acids were lost to the animal. This illustrates the importance of ensuring that the various elements of the total diet are adequate to provide the nutrients that the animals require.
In some situations the recommendation is made to reduce or eliminate the grain portion of the diet, for instance, to slow the growth rate of a foal exhibiting DOD, or to reduce the caloric intake of an obese horse. This practice may indeed reduce caloric intake, but amino acids, vitamins and minerals in proper amounts and balances are still necessary for healthy growth and development of young horses and maintenance of adult horses, and pasture and/or hay alone is not likely to supply adequate amounts of all the necessary nutrients. In these situations, a “supplement” is necessary to balance the diet so that all the nutrient requirements are met without adding calories that would speed the growth rate or increase obesity. The nutritionists at Purina Mills designed the Nature’s Essentials line to address such issues. For horses that need to reduce calories, Nature’s Essentials Born to Win or Mare and Maintenance are designed to provide the vitamins and minerals as well as amino acids that are usually lacking in forage-only diets.
It can be fairly complicated to determine if a horse’s feeding program is meeting all the nutrient needs of the horse without deficiencies, toxicities or imbalances. That is why LOL Purina Feed has invested decades of research into horse nutrition and feeding. The veterinarians and Ph.D. nutritionists at Purina identify nutritional challenges horses are facing and then conduct studies to determine the very best combination of ingredients and nutrients to address those challenges.
Nutritional Supplements - "Too Much of a Good Thing?"
Katie Young, Ph.D.
Consulting Equine Nutritionist
LOL Purina Feed
