Dr. Michelle Arnold, UK Veterinary Diagnostic Laboratory
Botulism is a disease caused by one of the most potent toxins known to man. This toxin is produced by Clostridium botulinum, a Gram-positive bacterium from the Clostridia family. This bacterium survives in the environment as a "spore" and contaminates plant material during harvest. For the bacteria to multiply and produce toxin, an anaerobic ("without oxygen") environment must be maintained. Under certain conditions, round bale silage ("baleage") can provide the correct place for botulism toxin to form. In the absence of oxygen (as is found in wrapped hay) and a pH greater than 4.5, the spores enter a vegetative state, multiply and produce toxin.
This toxin, once consumed and absorbed into the blood stream, blocks transmission of nerve impulses to the adjacent muscles. Two forms of the toxin, Types B and C, occur most frequently in Kentucky 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 rations of cattle.
Baleage is an increasingly popular alternative to baling dry hay that allows shorter hay curing time and saves valuable nutrients in the face of approaching adverse weather conditions. Baleage 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 long plastic tube or individually 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 tightly baled and quickly wrapped in 6 or more layers of UV-resistant plastic will undergo fermentation, a process that should drop the pH of the feed below 5.0 (ideally below 4.5) where spoilage organisms do not grow well.
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) but can occur with any type forage. If fermentation is restricted, it is critically important to maintain the integrity of the wrap to keep an anaerobic environment in the sealed bale and preserve the silage.
If wrapping is delayed or there is damage to the plastic covering, spoilage may result, which supports the growth of Clostridial organisms. On the other hand, very wet, non-wilted, and/or overly mature forages wrapped for baleage have less soluble sugars available for completion of fermentation and are also at an elevated risk for botulism toxin formation. Bacteria from the Clostridia family thrive in wet environments where forage moistures are in the higher 67-70% range; greater than 70% moisture is very high risk for Clostridial growth and spoilage.
Prevention is based on ensuring proper harvest and preservation of wrapped forages and maintaining proper feed out rates to reduce the risk of growth of organisms dangerous to cattle. Correct moisture content is of primary importance; there is a field method to assess moisture that will yield a general idea of moisture content but there are far more accurate methods available.
Achieving the highest bale density possible, especially with high internal core densities, removes the maximum amount of oxygen with few air pockets. Wrapping the bales quickly after baling with a good quality plastic, preferably with an ultraviolet inhibitor and 6-8mm thickness, and using multiple (4-6) layers will extend the storage time. Bale weight can be a safety and equipment issue.
It is advisable to test the pH and moisture content of your baleage at the very least to insure adequate fermentation before offering it to cattle. Samples can be submitted to a forage laboratory such as Dairy One for quality and a fermentation profile. This type of forage analysis will include a pH and volatile fatty acid profile and will give a very good idea of the quality of feed produced.
This is a common practice for corn silage and one should consider this with fermented forages of all types to avoid health risks. 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 techniques from time of harvest through feeding.
As always for more information feel free to contact myself, T.J. Adkins, at the Pulaski County Extension Office 606-679-6361. We are always happy to help.