The poll is the top of a horse's head just behind the ears, over the first two vertebra of the neck. In a typical posture, the poll is the highest part of the horse other than the ears. The crown piece of a bridle passes across the poll as it goes over the top of the horse's head.
If the horses injures it head or its bridle chafes the poll area this can allow bacteria to invade. An infected animal may show no symptoms for as long as two years. But then the infection will cause swelling, large swollen areas and even a discharging fistula on each side of the neck.
This is very rare now, but historical was quite common with working horses, and was referred to as "poll evil". The name of the condition was derived from the aggressive way a suffering horse would act, to avoid being bridled and experiencing more pain.
A similar condition at the top of the shoulders was referred to as fistula of the withers or fistulous withers. In severe cases the swellings will burst and allow for secondary infections, and the horse may suffer from lameness and lethargy.
The condition of poll evil may go back almost as far as the domestication of the horse. A case has been described based on the remains of the horse that lived in the first millennium BC.
For most of the period treatments would have been largely ineffective, mainly mechanical interventions like draining of fluids. There were also many folk remedies such as poultices and treatments that did more harm than good such as the use of caustic chemicals.
Poll evil is now very rare in developed nations for multiple reasons:
- Poorly designed stables with low doorways ad ill fitting tack is less common now that most horses are used in sport and leisure rather than labor. thus the kind of injury that can lead to poll evil is less common.
- The types of bacteria that cause the condition (such as Brucell abortus) are now less common. Horses with infections in the 1930s would be found to positive for Brucella abortus about 5-40% of the time, by the 1970s this rate had dropped to 2%. The main source of infection was most likely cattle or pigs that have Brucellosis. In cattle this infection was traditionally referred to a "Bang's disease".
- The condition can now be more effectively treated with antibiotics.
Suppurative atlantal bursitis
In modern terms poll evil is called suppurative atlantal bursitis and fistulous withers is referred to as suppurative supraspinous bursitis.
It is more likely to occur with horses that are in contact with wildlife like elk or bison who may still carry brucellosis, and the condition is more common in older horses.
This condition is also still common in less developed areas such as parts of sub-Saharan Africa where Brucella abortus is still a common infection of livestock.
Humans can also contract Brucelosis by being in contact with infected animals. It can cause symptoms such as fever, fatigue and joint paint.
- Fistulous Wounds. Poll Evil
This term signifies a wound on the poll, or that part of the neck immediately behind the ears. It usually consists of one or more sore places in the skin communicating by pipes (sinuses) with a cavity...
- Fistula of the withers and poll-evil : Merillat, Louis A. (Louis Adolph), 1868- : Free Download &
Veterinary Library's copy part of the John A. Seaverns Equine Collection