How Much is Too Much? The Dangers of Over-Supplementation
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By Megan Arszman
If there were a supplement that claimed it could help your horse win a World Champion title, would you add it to your horse’s daily rations? In your mind, you’re probably thinking, “Well, as long as it doesn’t hurt my horse, it can only help him, right?”
For years, many horse owners haven’t thought twice about adding a supplement to their horse’s diet, believing that any extra help is good help. Sometimes it’s just to help shine the coat, make the hooves grow strong, or add some bulk muscle. If it’s offered on store shelves, it has to be safe… Right?
Not exactly. Even the simplest supplement can cause slight, or even severe, side effects if not researched thoroughly and handled appropriately.
Human Manipulation
While horses are grazers by nature, their domestication has given humans control over what they eat, how much they eat, and how often they eat. Just like feeding your family, you control the intake of nutrients in your horse’s meals, so it’s important to be as educated as possible about what you’re pouring into your horse’s feed bucket.
“Owners need to understand that although the FDA (Food and Drug Administration) classifies nutritional supplements as GRAS (‘generally recognized as safe’), veterinary nutritional supplements remain largely unregulated,” explains Stacey Oke, DVM, MSc. “This means that the FDA is swamped and can’t ensure the quality of all of the equine supplements on the market.”
Oke points out that nutrients need to be consumed in balance. This is because excess ingestion of one nutrient can alter the absorption of other ingredients—potentially causing a deficiency. This was highlighted in a study conducted by Carey Williams, PhD, an equine Extension Specialist at Rutgers University on upper level, three-day Eventing horses. In that study, Williams and colleague Amy Burk, MS, PhD, a horse specialist from the University of Maryland, found that many horses were consuming higher than recommended levels of vitamin E, potassium, calcium, phosphorus, and magnesium. Over-supplementation of vitamin E (the most commonly supplemented antioxidant in horses) can lead to lower systemic beta-carotene levels, potentially causing a vitamin A deficiency if the horse doesn’t have regular access to fresh, green grass.
In the case of the Eventing horses, excessive vitamin E supplementation led to a vitamin A deficiency. This deficiency can lead to decreased immune function, night blindness, and reproduction issues.
“In an ideal world, a horse would graze on forage for most of the day and obtain all six essential nutrients, naturally,” Oke says. “Unfortunately, poor quality hay, drought, hay shortages, and modern equine management practices can interfere with horses obtaining sufficient nutrients.”
The six nutrients Oke refers to are water, carbohydrates, protein, fat, vitamins, and minerals.
Many horse owners believe that purchasing supplements by the tub to provide “more” or “better” nutrients is in their horse’s best interest. But thanks to numerous companies offering supplements and their effective advertising campaigns, we might be overdoing it.
“The recognition of the importance of nutritional supplementation for various health conditions, such as joint disease, skin and coat, immune systems, or geriatrics has spurred a widespread use of supplements,” Oke says.
Many times, an owner will purchase a supplement off the shelf because of the claims on the label that the product will help their horse live a longer, healthier, and happier life. Rarely are veterinarians or equine nutritionists consulted, which is a big problem, Oke says. The extra time, and perhaps money, spent working with specialists can help you save in the long run, because over-supplementation can be expensive, wasteful, and potentially dangerous to your horse’s health.
Be Educated
One of the reasons owners tend to over-supplement their horses is because they tend to overestimate how much work their horse does. There is a vast difference between light, medium, heavy, and very heavy exercise.
Horses on the show circuit can be classified anywhere as undergoing light exercise (one to three hours of exercise per week) to heavy (four to five hours per week). Note that very few horses classify as heavy workers.
If your horse doesn’t have any special dietary needs (as specified by your veterinarian or nutritionist) and is in the light or moderate exercise category, good-quality pasture or hay alone can meet his or her nutrient requirements.
In order to know if your hay is providing the needed nutrients, you should have your hay tested.
Hay Testing Tips:
• Sample bales of hay from all around your stack. Nutrients in the soil tend to vary from one spot to the next, so it’s best to test from more than one bale (a minimum of 15 bales for a solid test).
• Use a hay corer, which can be borrowed from your county extension agent or hay broker.
• Sample fresh grass. Randomly select a composite sample throughout your pasture and be sure it’s dry before sending it to a lab.
• Use a lab that has passed the Forage Testing Council certification process for an accurate test.
When to Supplement
Despite the potential negative aspects of over-supplementing, it’s important to recognize that supplements aren’t universally evil. There are times when supplementing is needed—as long as your veterinarian has prescribed it as a course of action to battle issues such as joint disease, hoof conditions caused by a dietary imbalance, digestive support (colic, diarrhea, etc.), skin and coat ailments, poor diet, general illness, etc.
Oke advises horse owners to be “SMART” about supplements:
S – Shop Around. Do your research (after consulting your veterinarian or equine nutritionist) for what’s safe, effective, and contains the appropriate type and amount of active ingredient(s).
M – Monitor Response. Nutritional supplements will take a few months to really show a notable response; have patience.
A – Avoid Double Dipping. Know what your horse is eating to avoid feeding more than needed. Many commercial feeds already have additives for supplementation, so read the feed label before purchasing supplements.
R – Re-evaluate Your Choices. Some nutrients don’t need to be supplemented 100% of the time. For example, if you’re adding electrolytes during the hot summer months to combat dehydration and fatigue, you don’t need to feed electrolytes during the winter months when there’s not a whole lot of sweating occurring.
T – Talk to an Expert. Your veterinarian is a wealth of knowledge.
Too Much Love Can Be Dangerous
Over-supplementation can result in more concerning effects than money disappearing from your wallet. Entire textbooks have been devoted to the topic of nutrient interactions, herb-nutrient interactions, and even drug-herb-nutrient interactions reported in horses, Oke says. Such interactions can either cause a decrease or increase in efficacy of one or more product ingredients. If a decrease occurs, then the drug, herb, or nutrient will not be exerting the desired effect. More concerning is if an increase in ingredient efficacy occurs then side effects could be negotiable.
As mentioned earlier, nutritional supplements are classified as GRAS; however, there is still a risk of a substance being toxic or harmful. Mild adverse events include hives, mild diarrhea, and mild weight loss. Most of these cases are rarely reported to the FDA or the manufacturer, but owners are encouraged to do so if they see any sort of reaction in their horses.
Contamination of products with heavy metals or other environmental contaminants, in the case of herbs and botanicals, and cross-contamination with other products manufactured in the same facility have been reported. Choosing a quality supplement can minimize the risk of poor-quality supplements.
Over-supplementation can be dangerous for the environment as well. For instance, excessive electrolyte supplementation can result in the nutrients being lost in urine and feces. The excess nitrates can leach into waterways, leading to an excess growth of algae, thus potentially killing off fish and other aquatic wildlife.
Proceed With Caution
Every horse owner’s goal is to have a healthy, happy horse, and you want to do right by your steed. While nutritional supplements are easy to find anywhere, you want to treat them with kid gloves. Work with experts in your area to find out exactly what you’re feeding your horse and make a plan to fill in any holes. Administering supplements without a veterinary diagnosis and without following the manufacturer’s directions can delay a proper diagnosis, decrease the effectiveness of therapy, and negatively affect the quality of your horse’s life.
