Many veterinarians, like many medical doctors, have an equivocal relationship with the concept of supplementation. Precise evidence for efficacy is lacking in many cases, and even where data exists it certainly doesn’t rise to the level of proof they are used to with pharmaceuticals. The case for dietary shortfalls resulting in nutrient deficiencies is not as clear cut as it may be for human populations. And many vets are also suspicious of the quality control in the dietary supplement realm and believe that is is all too easy for an owner to purchase a supplement for a pet that has too little of the stated active ingredient or might be contaminated with undeclared substances.
Less is more
Horses are a prime example for the case of less is more. Horses are indestructible-looking to the uninitiated eye. But these animals, which evolved to survive on open grasslands, can be remarkably delicate in a typical recreational setting, however well they may have adapted overall to being domesticated. Horses are adapted to roaming far and wide and eating large quantities of rough forage, and can be plagued by digestive issues when confined and fed more nutrient dense feed.
Dr. Tanja Hess, DVM, an equine nutrition specialist at Colorado State University, said the case for routine supplementation in horses is flimsy at best in her opinion. Horse owners, in their zeal to do the best for their companion animals, can in effect love them to death, she said.
“People usually give too many supplements, that is the rule,” said Dr. Hess said. “They give them because they think they are good based on their own experience. More is better, and therefore they over-supplement.”
Knowing baseline feed values
Dr. Hess said horse owners, even with the best of intentions, can inadvertently make mistakes when supplementing their horses’ feed. Without knowing what a horse might be lacking, and without a clear understanding of how a horse’s physiology differs from that of a human even though they are both mammals, owners may inadvertently do more harm than good. She said that in the data CSU has gathered, about 85% of supplements given to pet animals are purchased from non-veterinary sources.
“Too much is not good,” Dr. Hess said. “Some mineral supplements might upset the whole balance. For example, you could have a case in which orthopedic disease could develop because the balance of zinc and copper is off.”
Horses are naturally browsers, and will chose to eat a wide variety of plants when they are available. Problems can arise when they are fed a low quality diet or are turned out and pasture is poorly managed.
“People really should know what the content of their pasture or their hay is. If they can’t have it tested, they should at least know the common values for pasture or hay in their area,” she said.
According to CSU, for example, the average pasture in the Denver-Fort Collins area of Colorado where many horse owners in the state live is relatively nutrient deficient. In that area it takes at least about 28 acres of average-quality, non-irrigated pasture to adequately nourish one horse. If that acres-to-horse ratio is smaller, as it would be in most cases, supplemental feed with hay or alfalfa is necessary.
Diets in omega-6 fatty acids can be pro-inflammatory
Even so, Dr. Hess said, outright nutrient deficiencies in recreational horses are rare if pastures or hay are of average quality. What’s more common are problems that arise when too much food is given, or if ‘rich’ food, such as lush pasture when it first greens up in the spring, is offered all at once. Horses that have eaten too much fresh grass in one go can develop a digestion-related inflammatory condition known as founder (laminitis), which causes the all-important connective tissue in the hooves to soften and weaken. Foundered horses can be rehabilitated, but the condition can be fatal when the horse becomes too lame to stand.
“We know that 56% of the founder cases are related to dietary issues, and about 48% are related to feeding on lush pasture that is rich in sugars,” Dr. Hess said.
Dr. Hess said knowing breed differences and differences among individual horses are critically important. Horses known as “easy keepers,” in other words those that thrive on less and poorer feed than their peers, are analogous to humans who might more easily develop Type 2 diabetes. Diabetes is rarely seen in horses, but some horses can develop insulin resistance, which might come on with too much grain (which is related to colic more than laminitis) or free choice supplementation. Horses offered free choice forage may get overweight and if they develop a metabolic disorder could then develop laminitis. Horses are not very good at digesting the kind of concentrated carbohydrates found in grains, Dr. Hess said. Some owners, seeking to pamper their horses, could easily feed too much grain.
With all of those caveats, Dr. Hess said that some ingredients have been shown to be effective in horse supplementation. Glucosamine and hyaluronic acid have been shown to be helpful in joint support, and chondroitin has been shown to be absorbed into horses’ blood after being added to feed. (Whether it does anything after getting into the blood is less clear cut, she said.) In addition, omega-3 fatty acids have been shown to be useful in managing inflammation. Probiotics in theory might be useful, but Dr. Hess said there is not much data on dosages, so it is hard to know how much to give, considering the vast digestive tract of a horse compared to that of a human.
Getting too much home cooking
Knowing what a pet really needs as opposed to what ‘sounds right’ is critical for the animal’s health, agreed pet nutrition specialist Dr. Lisa Freeman, DVM, of Tufts University in Boston. Dr. Freeman, like Dr. Hess, is not sold outright on the notion that every dog or cat needs a little extra something.
“Nutrient deficiencies in pet animals like dogs are not very common. People are often wanting to give a multivitamin to their animals but there is not a good reason if they are feeding a good quality manufactured food,” Dr. Freeman said.
Dr. Freeman said where she does see dietary problems is with those owners who decided out of love to go the extra mile and cook their own meals for their pets. These ideas are often formulated on an owner’s mistaken or romantic notions of what an animal might have consumed in the ‘wild.’
“Where we do see deficiencies is with home cooked diets that are not formulated by a veterinarian or an animal nutritionist. It’s easy to make the food, but it is not easy to make a nutritionally balanced diet. Close to 100% of home cooked diets that we have seen are nutritionally unbalanced,” she said.
Dr. Freeman said that joint health is one clear area at least, where supplementation could play a clear role as animals grow older.
“I do use dietary supplements for my patients where they are indicated. But when I use them, I want to use them very carefully and I want supplements that have good data on safety and efficacy and have good quality control. Our pet animals are living longer and are starting to show the common diseases of aging. Osteoarthritis is common among dogs and cats,” she said.