Thirteen cases of botulism in horses fed big bale silage.

This research describes an outbreak of botulism in horses and ponies in South East England that was potentially caused by their feed, which was large bale silage. The research suggests inadequate fermentation in the manufacture of the plastic-wrapped silage as the reason for the growth of the bacteria that produced the toxin.

Details of the Outbreak

• The research reports on an outbreak of pharyngeal and limb paresis, both of which are characterized by weakness in muscles, in four horses and nine ponies in the south east of England.
• Nine of these thirteen animals either died or had to be euthanized for humane reasons due to the severity of the condition.

Evidence Pointing Towards Botulism

• From the clinical symptoms presented by the affected animals, botulism was suspected as the cause. Botulism is a potentially fatal illness caused by a toxin produced by the bacterium Clostridium botulinum.
• This suspicion was confirmed when tests showed the presence of type B botulinum toxin in the serum of one of the cases.

Source of the Infection

• All of the affected animals were found to be fed big bale silage, which is a common type of animal feed. Silage is fermented, high-moisture stored fodder which can be fed to ruminants or used as a biofuel feedstock for anaerobic digesters.
• The paper discusses how the conditions of fermentation in the manufacturing of this plastic-wrapped silage may not have been adequate to prevent the growth of the Clostridium botulinum bacteria.
• Upon the examination of a feed sample that the horses had been fed, it was determined that this was likely the source of the toxin that caused the botulism.