Mary Allen
Mold in the air and the feed pollutes the respiratory and gastrointestinal tract of a horse. It is often difficult to catch them.
Not only farmers but also horse owners are looking up at the sky with anxious eyes these weeks. The weather largely determines the quality of the hay, straw, and grain harvest. If feed and bedding get wet, they become an ideal breeding ground for mold. The approximately 300 known species reproduce by forming spores and can produce mycotoxins under suitable conditions. The fungi and their toxins can get into the horse’s organism together with the feed or be inhaled together with dust particles.
Depending on the type of mold, the amount of poison, and the individual animal, the consequences range from allergies and chronic coughing to cramps and liver, kidney, and nerve damage. Mold spores can also lead to diseases such as coughing without the formation of toxins. The first signs of mold poisoning are often tiredness and reduced performance, often several horses in one stable are affected. The problem: It is not always possible to tell at first glance whether the feed is contaminated or not. Hungry horses also eat rotten hay or musty oats. In addition, it is not easy, even for the veterinarian, to unmask mold as the culprit.
Exact Determination is Very Expensive
“Unfortunately, a blood test does not show whether mold is responsible for colic or other diseases. If mycotoxins affect the liver, elevated liver values in the blood can only determine that the liver is affected, but not what the cause is,” explains Annette Liesegang, Director of the Institute for Animal Nutrition. If there is a suspicion of mold infestation, all the feed, the bedding, and the rest of the stable environment must be examined carefully. To take a sample, collect a shopping bag full of stalks or grains from different places in the bale or feed bag, since the mold and toxins are rarely evenly distributed.
If a mold infestation is suspected in the laboratory through a sensory test (smell, appearance, structure) and a microscopic examination, a special laboratory can find out which type of mold it is and whether mycotoxins have been formed. The determination of mycotoxins is very expensive, so it is only recommended if there is reasonable suspicion.
Typical spoilage pathogens (storage fungi) in animal feed are, for example, Aspergillus (the toxins formed are aflatoxins – but these actually tend to grow under warmer conditions, or ochratoxin and citrinin – the latter is also found more rarely under our conditions!) and Penicillium species (toxins: ochratoxin, citrinin). However, toxins could also be produced by field fungi such as Fusarium (deoxynivalenol, zearalenone, diacetoxyscirpenol, T-2, fumonisin) or Alternaria (tenuazonic acid, alternariol).
Detective Work for the Veterinarian
Under local conditions, it is above all the combination of different mycotoxins that are known to be harmful. Which mycotoxin occurs depends on the feed and the influences during harvest and storage. In 2007, a study in 46 horse stables found low concentrations of deoxynivalenol (DON, Fusarium toxin) in eight straw and one hay sample. However, the connection between contaminated roughage and litter and the occurrence of colic and lung diseases could not be proven in this study. Most reports of this come from the USA and other warm countries (South America, South Africa).
“The veterinarian should first rule out other possible causes by taking a detailed anamnesis and examining the animal. A connection between the symptoms and a moldy feed can only be assumed, but usually not proven. What is certain, however, is that hay or grain, which have significant hygienic deficiencies, are not suitable as horse feed,” says Liesegang. The difficulty of making a clear diagnosis often means detective work for the veterinarian in practice: he has to rule out other causes for the horse’s symptoms. Many possible indications feed contaminated with mold is causing problems such as coughing – for example, if other horses eating the same feed have similar problems or if the symptoms improve after a change of feed. However, you usually have to do without definitive proof that a disease was caused by mold.
But it doesn’t matter whether you can determine that the moldy carrots were to blame for the colic or not: Feed and bedding that are contaminated with mold have no place in the box or the trough. Horse owners should regularly check the quality of the horse feed, even if they are in a boarding stable. If the oats smell musty, if the hay is dark and dusty, or if the apples have moldy spots, they should be disposed of immediately on the manure heap – this may be expensive in the short term, but in the long term, it saves a lot of veterinary costs.
Less Dust Means Less Mold
Ideally, the fight against mold begins in the field, because under optimal harvesting conditions mold does not develop in the first place. Of course, it is also important that bedding and feed are stored properly, i.e. dry and clean. Even the best hay rots when it gets wet in the barn. Preventive measures in the fight against mold also include cleanliness and good air circulation in the barn, whereby drafts should be avoided. This reduces dust exposure, which in turn reduces the spread of mold spores.
Various feed manufacturers now offer mycotoxin binders. These contain clay minerals or yeast cell components that are intended to bind the toxins before they enter the bloodstream via the intestine. The mycotoxin binders are used to detoxify affected animals, but it is sometimes recommended to mix them with the feed as a preventive measure. According to Liesegang, however, this is only of limited use: “Before you think about feeding mycotoxin binders, suspicious feeds should be examined in the laboratory.”
However, it should be noted that in the case of mold infestation, it is not only the mycotoxins that cause problems such as colic or liver damage but the mold spores, even without the mycotoxin contamination, which irritate the respiratory tract and cause coughing or chronic lung diseases such as COPD. And mold spores that are inhaled are not affected by the mycotoxin binders.