– Dr. Michelle Arnold, DVM- Ruminant Extension Veterinarian (UKVDL) and Dr. Jeff Lehmkuhler, Beef Extension Specialist, University of Kentucky
Round bale silage (or “balage”) is an alternative to baling dry hay that allows shorter hay curing time and saves valuable nutrients in the face of approaching adverse weather conditions. It is a combination of hay and silage making and has certain advantages and disadvantages over other forage preservation systems. Balage is simply forage of a relatively high moisture content that is baled with a round baler and then stored in a sealed container, usually a plastic bag or wrapped in plastic, to keep oxygen out. Both grasses and legumes can be preserved by this method if proper techniques are followed. Forage cut at the correct stage of maturity, allowed to wilt to a 40-60% moisture range, then baled and wrapped at the proper moisture content will undergo fermentation, a process that drops the pH of the feed below 4.5 where spoilage organisms (especially bacteria from the Clostridial family) will not grow. Problems arise when there is a lack of adequate fermentation to reach this low pH, which occurs most often with small grains (rye, oats, wheat, barley). Wet, non-wilted, and/or overly mature forages have less soluble sugars available for completion of fermentation. Clostridials thrive in wet environments where forage moistures are in the higher 67-70% range; > 70% moisture almost guarantees Clostridial activity. Baled silage is also more likely to spoil as compared to silage in traditional silos because of aerobic degradation of the carbohydrate due to delayed wrapping, poor moisture management, and damage to the plastic covering, resulting in the harmful introduction of oxygen.
Botulism is a disease 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 everywhere in the soil and contaminate plant material during harvest. In the absence of oxygen (as is found in wrapped hay) and a pH greater than 4.5 (poor fermentation), 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. Typically a large number of animals affected all 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. A toxoid for Clostridium botulinum type B (Bot Tox B, Neogen Corporation) is approved for horses and can be used in an extra-label fashion in cattle if a valid veterinary-client-patient relationship exists. This vaccine will not reverse clinical signs already present but may help to prevent new cases. 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. 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. Calves may exhibit extreme muscle weakness due to a lack of selenium. Your veterinarian is the best source of information to determine the cause of your problem.
Prevention is based on ensuring proper harvest and preservation of wrapped forages to reduce the risk of botulism in cattle. Correct moisture content and maturity of the forage are of primary importance. Also, achieving the highest bale density possible, especially with high internal core densities, gets out the maximum amount of oxygen with few air pockets. Wrapping the bales as soon as possible with a good quality plastic, preferably with an ultraviolet inhibitor and 6-8mm thickness, and using multiple layers will extend the storage time. If holes appear during storage, these should be covered immediately with tape. Store the wrapped bales on a north facing slope if available because prolonged exposure to the summer sun may cause the upper side and the south face of the bale to dry out, with the moisture condensing on the bottom or north face of the bale. A well-managed bale could end up developing a Clostridial prone pocket in dried out areas of the bale.
In summary, it is advisable to test the pH of your balage to insure 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. An outbreak of botulism in 2009 in Nelson County serves as a reminder 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. It is important to remember that thousands of round bales are wrapped annually with only a few cases of botulism occurring; the risk of disease is low if one applies the proper management from time of harvest through feeding.