The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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42 TheHorse.com THE HORSE August 2015 T he hay delivery truck has just pulled out of the drive, leaving behind stacks of expensive hay bales that are a leafy, verdant green, void of obvious mold, and … mmm … they smell so fresh! But wait, how do you know this is the best possible hay for your horse? Could there be hidden horrors lurking within? Equine nutritionists say the answer is a resounding yes. From toxins and molds to opossum droppings and animal carcasses, forage can contain a variety of harmful contaminants. "It is the owner's onus to look beyond the color, cut, crude protein and carbo- hydrate content, and the leaves, seeds, and stems to see whether or not you purchased good-quality hay or bought yourself a pile of lemons," says Kathleen Crandell, PhD, nutritionist at Kentucky Equine Research, in Versailles. Our goals in this article are to alert you to dangers associated with hay, suggest various ways to avoid forage fiascos, and arm you with the necessary tools to find (almost) flawless forage. But don't let these potential problems dissuade you from feeding hay-based diets! Most horses thrive on forage and forage alone, unless involved in heavy work, breeding, or lactation. Fungi (Including Molds) The fungi kingdom includes both molds and yeasts. Molds are plantlike organisms that derive energy from the organic material on which they live. They thrive in moist environments and can grow on forage before and after it has been cut for hay. In general, the faster hay dries after cutting, the less mold grows. "The presence of mold indicates that the hay was moist for some time before baling or that the hay was baled while it was still moist," explains Carey Williams, PhD, equine Extension specialist and associate director of Extension at Rutgers' Equine Science Center, in New Bruns- wick, New Jersey. "Moldy hay is generally unpalatable, which decreases intake." Moldy hay might not have been poor-quality to start with, but it gener- ally becomes such. This is because the mold- inducing moisture causes the tem- perature inside the bale to rise, and that excess heat damages the hay. Molds can also produce harmful toxins. Although these toxins are usually a bigger problem in haylage or silage (because of the warmer, moister conditions), moldy hay bales can contain sufficient quanti- ties of toxins to cause serious problems in horses. One example is aflatoxin, produced by Aspergillus spp, which can damage the liver and cause inappetence, depression, fever, tremors, ataxia (inco- ordination), and coughing. Researchers have proposed a possible link between aflatoxin exposure and recurrent airway obstruction (commonly known as heaves). Unfortunately, a barn-aisle examination of hay alone is not always an effective means of assessing hay quality. "While some molds are clearly seen or smelled, there are some sneakier mi- crobes that can pose a problem for your horse," warns Williams. One such example is the fungal endo- phyte Acremonium coenophialum, which can live between individual plant cells in tall fescue. "The fungus and fescue essentially set up a win-win situation," explains Williams. "It is a symbiotic relationship where the fescue 'protects' the fungus and the fungus produces chemicals such as ergovaline that are bitter and unpalatable to fescue-feeding insects." Fortunately, infected fescue ingestion is predominantly only of concern to those managing pregnant mares because it causes prolonged gestation and aga- lactia (lack of milk production). Most other horses can tolerate infected fescue, and pregnant mares can still be offered endophyte-free tall fescue. Just because your hay looks and smells nice doesn't mean molds, bugs, and weeds aren't hiding within. Be sure to inspect it closely before feeding it to your horse. DUSTY PERIN NUTRITION STACEY OKE, DVM, MSC TheHorse.com/Nutrition What's Lurking in Your Forage? Find out what hay contaminants could hurt your horses