Botulism is a deadly disease with a direct relationship to certain types of compromised forage fermentation. Historically, it has not been a common occurrence, but with a higher volume of baleage being made, the frequency has the potential to rise.
Clostridium botulinum is the culprit bacterium that produces the toxin. It grows under anaerobic conditions (no oxygen) and when the forage pH is greater than 4.5, notes Michelle Arnold, D.V.M., who is with the University of Kentucky (UK) Veterinary Diagnostic Laboratory.
“This toxin, once consumed and absorbed into the blood stream, blocks transmission of nerve impulses to the adjacent muscles,” Arnold writes in UK’s Off the Hoof newsletter.
Cereal forages are generally at the highest risk for growing clostridial bacteria, but it can occur in any type of harvested forage. Extremely wet forage (above 67% moisture) and very mature forage is also subject to poor fermentation and creating an environment where clostridia can thrive.
Arnold lists the following characteristics for cattle suffering with botulism:
1. Typically, multiple cattle will be affected with symptoms at the same time; some cases may present as sudden deaths. Otherwise, animals first appear dull, depressed, lethargic, and eventually become thin and dehydrated due to the inability to eat and drink.
2. Cattle will have progressive muscle weakness that may lead to recumbency (downers), depending on the amount of toxin ingested. Clinical signs are first observed from about 24 hours up to 17 days after exposure to the toxin.
3. Cattle will lose tone and control of their tongues. Without tongue control, a cow will have other associated signs such as a dirty nose, difficulty chewing and swallowing, drooling, and plunging the nose deep in a water trough to drink. Although animals may appear to chew hay or grass, there is an inability to swallow, so feed and forage may be seen to fall from the mouth or may be found within the mouth.
4. Back and forth movement of the lower jaw may be very loose, and the upper eyelid and tail tone are often noticeably limp.
5. Cattle may become constipated, raising the tail while straining. In addition, colic is sometimes observed, and a “hunched up” appearance is noted.
6. Most cattle that go down due to botulism toxin will die due to paralysis of diaphragm muscles, dehydration, or complications from being a “downer.” Cattle with a more gradual progression of signs and that maintain the ability to eat and drink may recover, although it can take 30 days or longer to return to normal function.
From a prevention perspective, Arnold recommends the following:
1. Harvest at the proper moisture content (55% to 65%), and especially don’t take chances harvesting wet cereal forages.
2. Wrap bales quickly and with enough plastic (four to six layers) to ensure an anaerobic environment. Maintain plastic integrity and quickly patch any holes with approved tape.
3. At a minimum, test bales for moisture and pH before feeding. Consider getting a fermentation profile analysis, especially for suspect baleage.
4. Use feedout rates that don’t leave bales in feeders for an extended period of time.