Mold and Mycotoxin Contamination in the Equine Diet
A subject that is currently receiving a great deal of attention both in the U.S. and abroad is that of feed-borne mold and mycotoxins. Mycotoxins are harmful metabolites which are produced by molds (fungi) which exist in the soil and vegetation such as feed, grains and foraging material. Mycotoxins form from mold before and during harvest in the field, and continue to form while being stored if conditions are poor after harvest. Mycotoxins are generally very stable and can persist for long periods of time. They act by inhibiting protein synthesis, which impairs the horse physiologically. The frequency of mycotoxin contamination of feed is increasing, most likely due to weather extremes leading to unfavorable growing conditions.
For years, livestock producers (poultry, ruminants and swine) have been aware of the dangers of contamination of feeds with mycotoxins, especially a toxin known as deoxynivalenol (DON), and have taken measures to decrease this feed contamination. Until more recently, there has not been as much focus and research placed upon exposure of horses to molds and mycotoxins, as well as what illnesses can arise from them.
So how are horses exposed to harmful molds and mycotoxins? Most often, exposure occurs via the ingestion of contaminated feed--concentrated grains, whole grains, hay, and even foraging in a green pasture. Less frequently seen methods of exposure include inhalation or transdermal entry. The extent of severity of exposure is dependent upon multiple factors, including how high the concentration of the mycotoxins is in the feed, how much feed is consumed, and are there multiple varieties of mycotoxins present which may interact with one another to create an even greater toxic effect.
The mycotoxins consist of a number of different varieties including aflatoxins, ochratoxins, deoxynivalenol (DON), fumonisins, zearalenone, and ergot alkaloids. Each of these toxins can be found in specific feed stuffs, including corn, wheat, oats, rye, barley, hay/straw, and grass. Two of the more commonly seen mold varieties are Aspergillus and Fusarium.
Aspergillus flavus and Aspergillus parasiticus are two molds which produce aflatoxin. These molds are generally seen more commonly in warmer temperatures and highly humid environments. Horses are especially susceptible to feed-borne aflatoxins, most frequently targeting the liver.
Fusarium mycotoxins (present on a global basis) thrive in soils ranging from North America, South America, and parts of Europe to Asia--anywhere that has a predominantly temperate climate. A number of different mycotoxins are produced by the various Fusarium variants, but horses are especially sensitive to feed-borne fumonisin, which can cause equine leukoencephalomalacia (moldy corn poisoning) and death.
There are a myriad of issues varying in severity which can result from the ingestion of mold and mycotoxins. Dermal inflammation and allergies as well as respiratory ailments such as blockage and heaves (Chronic Obstructive Pulmonary Disease) can be seen with mold ingestion. Clinical signs of mycotoxicosis in horses vary depending upon the type of mycotoxin ingested and the concentration of the mycotoxin in the feed. Some signs of ingestion include ataxia, tremors, fever, anorexia, weight loss, lameness, liver and kidney damage, reproductive issues/abortions, skin conditions, seizures and death. Some clinical signs following ingestion are acute, while others are chronic. The horse’s age, work-load, stress-level, nutritional status and immune status all factor in to determining how severe an impact the toxins will have.
Identifying cases of exposure to mold and mycotoxins can be a difficult process. Clinical signs can be indicative of ingestion; however, many signs are non-specific and could be caused by a variety of illnesses or toxins. If mold or mycotoxin ingestion is suspected, samples of all feed, hay, etc. should be submitted to a reliable laboratory for evaluation. Detecting and identifying a contaminant can be difficult, especially if the toxins are not evenly distributed throughout the feed or hay. Random sampling of small quantities may miss toxins that are only located in small portions of the feed.
Prevention of mycotoxicosis in horses must occur at numerous stages during the growing, harvesting, processing and storage of feeds and hay. The first step in control and prevention is through proper agricultural practices including crop rotation, soil cultivation, and insect and weed control. Once feeds have been harvested, it is essential that they are dried to below 13% moisture and stored at that moisture, necessitating ideal temperature, humidity and ventilation in storage areas. If grain and hay can not be stored in an ideal environment, then mold inhibitors should be considered. As well, organic and inorganic binders (which have been properly evaluated for safety and efficacy) can be added to the feed in order to prevent the absorption of toxins by the digestive tract.
In conclusion, it is essential that feed, supplements, and hay be acquired through reputable feed companies or other suppliers. It is very difficult to completely avoid all exposure to mold and mycotoxins; however, if the feed is produced, processed and stored using proper protocol, the likelihood of contamination will be greatly reduced. Hay and grain should always be stored in a dry location, and feed should ideally be kept in airtight bins to prevent moisture, insects, or rodents from accessing it. All food should be inspected at each feeding to ensure that it is mold-free. If hay or grain is identified as having been contaminated with mold, it should be discarded immediately. Simply removing mold visible to the eye will not eradicate the spores and mycotoxins that are still present in the feed and hay. If a bale of hay or a bag of grain has any visible signs of contamination, the entire bale/bag should be discarded, not just the portion that is visibly affected. These simple measures should go a long way in reducing the likelihood of your horses being exposed to contaminated food.
