Botulism has gained more notoriety in the press over the last few years, especially in areas where herds of cattle have suffered big losses and get into the local news. We see it less commonly in sheep but they are at serious risk from exactly the same disease. A recent case in the practice highlighted the need to be vigilant in all species.
Botulism presents in sheep initially with the animal walking slightly abnormally and may display odd head or ear carriage somewhat reminiscent of listeria. She may look slightly lame or she may be staggering slightly like she’s had one too many at the local pub.
The disease is caused by a toxin produced by the bacteria Clostridium botulinum. This toxin binds where the nerves would usually signal to the animal’s muscles to contract. This binding prevents the neurones transmitting their messages to the muscles and so the animal becomes progressively weaker, floppy even, until eventually laying down and then with her head flat out. By this stage, if botulism is a real consideration, the tell tale sign can be seen by pulling on the tongue… If there is no muscle tone there, or “pull back” then botulism is extremely likely to be the cause.
Treatment is almost without exception a futile effort although there is a vaccine that will work quickly to protect the flock. The focus should be on this and in identifying the source of the toxin and immediately acting to eliminate it.
The bacterium is found in decaying carcasses and sometimes vegetation. Most commonly, the source is chicken manure especially broiler muck since the odd carcass will remain.
In the case pictured, chicken muck was being stored in proximity to the housed sheep. Effluent was getting onto the tyres of the machine used to feed up housed sheep and this was enough to contaminate the forage. The flock was vaccinated to protect from further risk and the contaminated feed immediately removed. Feed was spread by hand thereafter and no further losses were seen.
The vaccine is one of the cheaper vaccines around despite it being imported and requiring a license. I therefore advocate protecting any flocks at risk of coming into any contact with chicken manure even if the fields being grazed have not had manure directly applied. I have even seen cases where neighbouring fields across a road have been the source of deaths. In these cases it is assumed carrion crows, foxes or wind have moved enough material to intoxicate the animals.
Diagnosis: The clinical presentation described and pictured above, combined with a history of chicken manure (or some other carcass) is usually enough to conform a diagnosis. Testing is very rarely carried out due to cost and the fact it involves unpleasantness to mice in a Dutch laboratory somewhere.
If you have any concerns about minimizing the risks of botulism to your flock, please get in touch with one of the vets.