BEWARE! - BOTULISM

Dr. Clell V. Bagley, D.V.M.
USU Extension Veterinarian

    Producers changing to the use of baleage should be aware of the potential for botulism and take steps to prevent it. It is not the baleage that is the problem but spoilage. Anytime forage spoils instead of fermenting (for silage) there is a definite opportunity for the development of botulism. Corn silage, bagged in the large plastic silage bags, has also produced botulism at points of punctures or rodent penetrations through the plastic. These sites allow air entry and spoilage instead of ensiling. The same process can also occur even in upright silos if air is allowed to enter.

    Botulism is caused by a very potent toxin produced by the bacterium Clostridium botulinum. This bacterium is commonly present in soil and just needs the right environment to grow and produce the toxin. Horses are even more susceptible to the toxin than are cows. One of the critical factors which allows growth of the bacteria is a pH above 5. With proper ensiling, the pH soon drops below this level and prevents bacterial growth.

    "For a variety of reasons, baleage usually does not undergo an extensive fermentation. Furthermore, the rate of fermentation is much slower in baleage than in conventional silage. The slower and less extensive fermentation that occurs in baleage means that the pH of baleage can remain relatively high for long periods of time after the forage is wrapped or bagged. Under normal conditions, conventional hay crop silage containing 40 to 50% dry matter (DM) will obtain a pH < 4.5 within one week of ensiling. A pH of 4.5 or less is generally indicative of a good, complete fermentation. When baleage is made from forage containing less than 40 to 50% DM, often the pH does not drop below 5 and can remain above 6 for more than 7 days post-ensiling. Baleage is an unstable product because of its high pH. When anaerobic conditions are compromised (i.e., the bag tears), the forage will undergo aerobic deterioration very quickly."

    "Recommendations: the growth of Clostridia sp. is inhibited in feeds containing low concentrations of water and by keeping pH less that 4.5. As mentioned above, the pH of baleage often is considerably higher than 4.5; therefore, wilting forage to more than 30% DM (40% DM is better) is essential. Clostridial contaminated silage has a very offensive odor (putrid and ammonia smell). Baleage (or any silage) with those odors should not be fed. Baleage that is covered with mold should not be fed (it is much more likely to harbor Listeria monocytogenes, another bacterial problem). The mold indicates that the pH of the silage is high and Listeria and/or Clostridial contamination is possible. Farmers may wish to purchase an inexpensive pH meter so that the pH of bales can be monitored. Those bales with pH greater than about 6 should be discarded and bales with pH between 5.5 and 6 should be examined closely for molds and evidence of Clostridia (ammonia smell)."1

    One method that has been used to measure the pH of silage is as follows: take a small plastic container (500 to 1,000 ml = 1 pint to 1 quart), pack it about half-full of silage, then add water to cover it (a sort of silage slurry). Mix it all up and measure with a pH meter. (Hand-held pH meters are available.)

    Clinical signs of botulism poisoning include a flaccid paralysis that is progressive. The animals tend to lie down more than usual and can still get up if encouraged but their muscles will soon begin to tremble while they are standing. They want to eat but there is weak tongue tone which causes difficulty in eating and swallowing. If the tongue is pulled out a little, they will have difficulty retracting it back into the mouth. They will eventually be unable to rise and may be mistaken for cases of hypocalcemia or ketosis but don't respond to treatment.

    Forage quality is critical for good nutrition and animal health, regardless of how the forage is harvested and stored.
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1Ohio Veterinary Newsletter, January 1993. ©