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Test pH to ensure adequate fermentation

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By Rick Greenwell

We are sharing with you what causes botulism in cattle after an outbreak in Nelson County a couple of months ago. A lot of local people are gun shy over their cattle dying.

A recent outbreak of botulism (“forage poisoning”) in Nelson County serves to remind us of the potential for deadly consequences from poor quality feed. In December 2009, round bale oatlage was fed to stocker calves that resulted in the deaths of 90 head. Samples of the rumen contents and the oatlage were sent to the Botulism Diagnostic Laboratory at the University of Pennsylvania where both tested positive for the Clostridium botulinum Type B spores and preformed toxin. Further analysis revealed a pH of 6.8 in the forage-the perfect environment for a disaster.  The cool, wet spring of 2009 prompted many producers in KY to wrap the first cutting of hay; essentiallypacking large round bales at high moisture content into individual plastic bags then sealing them to keep oxygen out. Forage cut at the correct stage of maturity, allowed to wilt then baled and wrapped at the proper moisture content will undergo fermentation, a process that drops the pH of the feed to a range where spoilage organisms will not grow. Problems arise when there is a lack of adequate fermentation to reach this low pH. This can occur most often with small grain (rye, oats, barley) haylage because fewer soluble sugars are available for completion of the fermentation process.

Botulism is caused by one of the most potent toxins known to man. This toxin is produced by Clostridium botulinum, a spore forming anaerobic Gram + rod. These spores are found in the soil and contaminate plant material during harvest. In the absence of oxygen and a pH greater than 4.5 , the spores enter a vegetative state, multiply and produce toxin. Two forms of the toxin, Types B and C, occur most frequently in KY cattle. Type B is associated with improperly fermented forage while Type C occurs from the accidental feeding of dead birds, dogs, cats or poultry litter contaminated with dead birds in the ration of cattle. Both types produce the same characteristic clinical picture in cattle including:

1. A large number of animals affected at once

2. Progressive muscle weakness leading to recumbency (downers) over a 2-5 day period of time, depending on the amount of toxin ingested. Signs may develop as early as 24 hours to as many as 10 days after ingesting the toxin.

3. Decreased Tongue Tone-The “classic” feature of botulism. The tongue may actually hang from the side of the mouth as the disease progresses. Without tongue control, a cow will have other associated signs such as a dirty nose, difficulty chewing and swallowing, and plunging the nose deep in a watering trough to drink.

4. Constipation/Raising the tail while straining. Sometimes see colic (abdominal pain) and a “hunched up” appearance.

5. Death due to paralysis of muscles of the diaphragm.

Treatment consists of supportive care including administering fluids and propping cows up on their sternum. An equine and a bovine origin antitoxin is available but neither will reverse clinical signs already present. Generally, animals less severely affected that do not go down will survive. Dead animals must be disposed of properly (including rendering) as the meat is not safe for consumption.  

Diagnosis is difficult and is usually based on history and clinical signs. Rumen contents, feed samples, and blood can be analyzed for the toxin and can also be injected into mice and observed for death. Other possible causes of muscle weakness and downer cows include low blood levels of calcium, potassium or magnesium, ionophore toxicity (rumensin, lasalocid), organophosphate or carbamate insecticides, heavy metals such as lead, and infectious causes such as listeriosis or rabies. Your veterinarian is the best source of information to determine the cause of your problem.

In summary, because of the cool, wet spring and the potential for large numbers of deaths, it is advisable to test the pH of your small grain haylage to ensure adequate fermentation. To do this samples can be submitted to a forage laboratory and a fermentation profile requested. This will often include a pH and volatile fatty acid profile. This is a common practice for corn silage and one should consider this with fermented forages of all types. According to Dr. Garry Lacefield (University of Kentucky Forage Specialist) ,there is no way to look at silage or haylage and tell if botulism is a problem. It can be off color and have a less than desirable smell and still be safe. However, anytime you open a bag and the feed is slimy, off color and sour smelling are strong indicators something has happened resulting in improper fermentation and possibly formation of the botulinum toxin.