What's in Your Feed? (Contamination)

"Yuck!" you hear your friend exclaim from the feed room as you move down the barn aisle one evening, doling out flakes of hay.

"What is it?" you call over your shoulder.

"There are huge lumps of molasses in this bag of feed!" she replies, chucking one out into the aisle for emphasis.

Arms now empty of hay, you scoop up the offending object. It certainly is substantial. Breaking the golf-ball-sized lump apart with your fingers, you note that it seems to contain only clumped-together grains, fines, and molasses. A quick sniff confirms the familiar sweet feed smell.

"Well, it's kind of gross, but I don't think there's anything harmful in there," you call back. "I wouldn't worry too much."

Modern processing and packaging methods have conditioned us to expect near perfection in all our food these days, from perfectly shaped Os in our Cheerios to pristinely polished oats in the grain we buy for our horses. It's easy to forget that the grain mix in your feed room is the product of a very natural environment--a farmer's field. Consumers don't want that surrounding habitat--a couple of twigs, a pebble, a clod of dirt, or some weed seeds--working its way into the feed we offer our horses. We also don't want the feed mill's mixing and bagging procedures not to be perfect or yield products with inconsistencies such as a lump of poorly integrated dried molasses. Little imperfections that would probably go unnoticed in a cattle barn might be enough to evoke extreme reactions in an equine operation.

Contaminants in horse feeds are, to some degree, a fact of life, and would be even if it were possible to grow oats, corn, and barley in completely sterile conditions. Very often, what a horse owner sees as a serious feed contaminant is pretty innocuous to the horse. But, a few foreign substances have the potential to cause real health problems.

How do you sort out the harmless from the horrifying?

Risk Factors

One of the reasons it's important to keep a watchful eye out for feed contaminants is that the horse's digestive system makes him unusually good at absorbing certain toxins. Ruminants, such as cattle and sheep, ferment their feed before they absorb the bulk of the nutrients, and that fermentation process effectively neutralizes many potentially harmful compounds before they can cross the gut wall.

However, horses process their feeds in reverse order. Most of the nutrients contained in their diets are absorbed through the wall of the small intestine before the fibrous portion of the feed is pushed on to the fermentation vat of the cecum in the large intestine. As a result, there's ample opportunity for toxic substances to be absorbed through the gut wall and circulated throughout the horse's system.

The fact that horses have no reverse peristalsis reflex--they're unable to vomit--further complicates matters. The body can't forcibly eject objectionable substances that have made their way down the esophagus.

Fortunately for the horse, the same talented upper lip that allows him to graze selectively--choosing the plants he favors and rejecting the bitter, inedible, or poisonous ones--serves him well when he's eating grain. The majority of horses are fussy eaters and will easily sort out any foreign material that happens to be lurking in a scoop of oats or mixed feed. It's very rare to hear of a horse which has choked on a stick or stone. That's why it's usually not a big problem if you find a small particle or two of something from the landscape in your feed; chances are, it simply slipped past the feed mill's several mechanisms for eliminating contaminants, but will be detected by your horse and cause no harm.

The incidence of physical contaminants such as dirt or rocks in packaged grains is quite low because feed companies bend over backward to eliminate them before the product reaches the consumer. When grain first arrives at the feed mill from a grower's field, each batch is inspected visually for contaminants before it's accepted, explains long-time plant manager Bob Bruce of MasterFeeds, a large feed company based in London, Ontario, Canada. Any grain that has too high a percentage of foreign material--stalks, pebbles, dirt, weeds, or insect parts, for example--is rejected immediately. The grain will undergo several more sortings before it gets poured into a bag.

In the mixer, foreign objects like small rocks get stuck and are removed; a sifter allows heavy objects to fall to the bottom, where they're cleaned away at least once a shift. Magnets pull out any metal that might be hiding in the grain. Finally, most feeds are subjected to an aspiration process, which sucks up unwanted dust and fines, before feeds are bagged and sent to your local feed store.

The care feed companies put into their mixing processes is designed to ensure, as much as possible, that the consumer receives grain that is 100% uncontaminated. But some types of contamination might occur after the feed has been bagged and sent to the store. Insects, for example, can invade closed feed bags in the storeroom. When you open your bag of feed, you might find yourself staring at an unpleasant series of cobwebs and tiny pupae mixed in with the grain. That is distasteful, to be sure, but fortunately harmless to your horse.

"The feed doesn't sit long enough at the mill for insects to be a problem," Bruce says. "If you find moths or other insects in the bag, it's because the product has been sitting in the warehouse too long, or at the wrong temperature. It's a good idea to check the date the feed was made, and to always buy the freshest feed you can find."

Physical contaminants are the most common problem with packaged grain feeds, Bruce adds. But there are other, rarer forms of contamination that are of more concern to horse owners. Mold growth, in particular, has the potential to seriously affect your horse's health.

Moisture is the Enemy

When the moisture level in certain grains is too high, bagging or otherwise packaging them can quickly lead to fungus or mold growth. There are dozens of fungi and molds that can attack corn, oats, and barley, the three main grains found in most North American horse feeds. Not only does mold pose a threat to your horse's respiratory health when he sticks his nose in a bucket of "furry" feed, but some molds also exude poisons (called mycotoxins) that are potentially fatal.

Mycotoxins were in the news recently, having been initially implicated in the rash of foal deaths and early abortions in Kentucky broodmares. Further research has led scientists to hypothesize that the abortions probably were not caused by mycotoxins in pastures, but by cyanide from cherry trees possibly carried into pastures by tent caterpillars.

Mycotoxins certainly have the potential to cause reproductive, digestive, neurological, and athletic problems in horses. Add to that list paralysis, hypersensitivity, brain lesions, and a gradual deterioration of organ function, which in turn can affect respiration, feed efficiency, and growth rates in youngsters. The impact of mycotoxin-infected feed can be especially high in horses which are used for high-intensity sports or in gestating or lactating broodmares, because they usually have a higher grain intake than other equines. Also, it is known that the debilitating effects of the mycotoxins increase with repeated exposure. Other multiplying factors include heat stress, exposure to more than one mycotoxin at a time, over-crowding, exposure to disease, drug interactions, and malnutrition.

One of the most dangerous things about moldy feed is that most molds associated with the grains fed to horses don't affect the palatability of the feed. Without a change in the taste or smell of the ration, horses are likely to keep eating. Equine leukoencephalomalacia (ELEM), commonly known as moldy corn poisoning, is the mycotoxin-related syndrome with which horse owners are most familiar.

First identified in 1891, it is the result of a fungus called Fusarium moniliforme, which invades corn fields in the Midwest. Fusarium produces a toxin called fumonisin, which increases in concentration when corn crops are stressed during the growing season (outbreaks of ELEM are usually associated with drought or very wet conditions at harvest). When consumed in sufficient quantity over a period of at least one to two weeks, fumonisin causes liver or neurological problems as early as 10 days after exposure or as late as 90 days afterward.

Horses usually show incoordination and a reduced response to external stimuli at first, followed by circling or aimless wandering, hyperexcitability, pressing the head against solid objects, blindness, and partial paralysis. Eventually, affected horses become recumbent (always lying down). These symptoms are a result of extensive brain damage (necropsies reveal a rather horrifying liquifying of portions of the cerebral cortex), and horses which exhibit these symptoms usually die within 24 to 48 hours. Horses which survive often suffer life-long neurological defects.

For reasons that aren't yet clear to researchers, some horses with ELEM end up with liver disease rather than neurological damage. Weight loss, edema, hemorrhage, unthriftiness, elevated bilirubin (which can cause jaundice), and serum hepatic (liver) enzyme activity, and jaundice are the signs of moldy corn poisoning-related liver failure. This form of ELEM is believed to be more reversible with treatment than the neurological form. However, once more than half of the liver becomes damaged, hepatic disease can become chronic, resulting in a horse which loses weight even when fed more than adequately.

Horses are more vulnerable to moldy corn poisoning than any other livestock species, sometimes showing symptoms after exposure to levels as low as five parts per million. The survival rate usually depends on how much toxin the horse ingested and over what period of time, but it is estimated that less than 50% of affected horses survive.

How can you minimize the chance that moldy corn will find its way into your horses' feed buckets? You could, of course, eliminate corn from the diet completely, but other grains also have some potential to be infected with molds or fungus, so it's difficult to achieve zero risk. Feed mills, well aware of the dangers of moldy corn poisoning, go through several steps to ensure their grain is fumonisin-free.

"Moldy corn develops after the feed is bagged," says Bruce, "and it needs a high level of moisture. So when we get corn in the mill, we test it to make sure the moisture level is below 14.5%. Otherwise the whole batch is rejected."

Because the risk of mold increases when the seed coat of the corn kernel is compromised, all processed corn--whether it is cracked, flaked, micronized, or ground--is routinely treated with a buffered mold inhibitor. These non-toxic products are usually sprayed on the grain before it is bagged or mixed into a sweet feed or pellet formulation. Mold inhibitors are also useful for high-fat and high-molasses feed mixes, Bruce says: "You can improve the shelf life of a feed by months when you use one of these products."

Many documented cases of ELEM have been linked to the feeding of corn screenings, or off-grade or damaged kernels of corn. Therefore, using only top-quality corn, processed and examined by a commercial feed mill, improves your chances of getting fumonisin-free corn.

Fumonisin isn't the only toxin to develop in corn. Aflatoxin, which is produced by Aspergillus mold, is another common one. Other grains, such as oats and barley, also can have mold growth. As a general rule, however, poor growing seasons (which tend to produce damaged kernels) and a high moisture content are the biggest risk factors. So, choosing a feed with naturally low moisture (such as a pelleted ration) might be a wise move in a year when the growing season has been particularly tough.

Most pelleted feeds have a moisture level of only 12-13%, making them resistant to mold as long as they're stored in a cool, dry environment. If you prefer a sweet feed or other molasses formulation, you might want to use one that is sold in paper bags, which "breathe" and allow moisture to escape. You should try to completely use your feed supply within a couple of weeks--especially in hot, humid weather--and discard any feed that got wet or was in storage for more than six weeks in the summer.

Beware Ionophores

There's one other major contamination factor of which horse owners should be aware. There is a class of antibiotics commonly added to some beef cattle and poultry feeds to which horses are extraordinarily sensitive. As a class, these drugs are called ionophores, and they effectively aid feed conversion and weight gain in cattle under stressful conditions. The best-known is a drug called monensin sodium (trade names Rumensin, Lasalocid, and Naracin).

Ordinarily these drugs would never be found in horse feeds, but if a batch of feed intended for equines were to be contaminated, a dose of monensin of only 1.0 to 3.0 milligrams per kilogram of equine body weight would be enough to kill more than 50% of the horses that ate it. Death comes after hours of progressive weakness (especially in the hindquarters), incoordination, disorientation, colic, labored breathing, and profuse sweating. In horses which recover from this type of poisoning, there can be long-standing cardiac degeneration, unthriftiness, and poor performance, with the possibility of delayed cardiac circulatory failure.

Because ionophores are such a danger to horses, the best place to buy horse feed is from a feed mill that doesn't manufacture these medicated feeds at all.

"It's best not to have (monensin) in your plant in the first place," says Bruce. "But if you must buy your feed from a mill which incorporates these drugs in cattle rations, ask about the procedures used to flush the system between cattle and horse feed batches. After a medicated cattle feed is made, I'd want to see the mill run through a batch of non-medicated beef feed, then maybe a dairy and a pig feed, before anyone started making feeds for horses."

He adds that the companies that manufacture ionophores now make it easier to test for their presence by including micro-tracers--minute iron filings that exude a dye detectable in the lab.

Because ionophores are so toxic to horses, it's best not to recycle feed bags that might have been used at one time to package medicated cattle feed. Horse feeds should be stored separately from cattle rations, preferably in a separate area of the warehouse or barn.

Basic Precautions

Fortunately, increased awareness has made monensin poisoning an extremely rare event these days. As for other forms of contamination in feeds, you can limit the risk by following a few sensible precautions:

  • Deal only with reputable feed mills and buy only top-quality feeds (generally, price is a good indication of quality).
  • Inspect each bag of feed before you offer the contents to your horses. Look for obvious signs that the bag has gotten wet; examine the grain for mold, insects, and foreign objects; and make sure it smells as it should. A musty or "off" smell can indicate spoilage.
  • Check the date code on the feed bag or tag before you buy, and select the freshest bags you can find.
  • Ideally, buy feed in small batches and feed it within two weeks of purchase. If you must store feed longer, keep in mind that pelleted or dry extruded feeds should have a shelf life of six months from date of manufacture if kept in cool, dry, rodent-proof conditions; feeds with added molasses or fat should be kept for a maximum of three months.
  • If you are feeding a large number of horses and store grain in a silo, be aware that feed closest to the outside walls might be exposed to greater temperature fluctuations, moisture, and mold growth. The best plan is to maintain two silos so that you can completely empty and clean each one before you fill it with fresh feed.
  • In poor growing seasons, consider switching to a corn-free or pelleted ration to reduce the risk of ELEM and other mycotoxins.
  • Ask about your feed supplier's return policy.
  • If you find evidence of contamination, don't feed the product to your horse. Save it to show to your feed dealer, along with any other bags you might have purchased at the same time. The contamination might affect only one bag, or the whole batch. Your dealer will want to trace back the feed to its origins and address the problem with all of its customers.
  • Store feed in rodent proof containers in a cool, dry environment.
  • Do not feed any feed in which you find a dead animal, since there is a serious risk for botulism.

Your vigilance for feed contamination is the best prevention against problems for your horse.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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