Sleepy foal disease is not common in South Africa but has been seen mainly in Warmbloods and other breeds from imported lines. This disease is caused by the bacteria Actinobacillus equili. Recently a new subspecies, A. haemolyticus has been isolated from foals showing typical symptoms. The transmission of sleepy foal disease is from a carrier mare that infects the newborn as it passes through her bith canal on its way out into the world.
Sometimes the foal is infected before birth and the mare may abort or give birth to a lazy-looking foal which survives for about 24 hours. Most foals, once they are born, become hyperactive within a very short time. The sucking reflex is present within 30 minutes, they are standing and moving well within one to two hours and able to follow their mothers at a walk, trot and canter very soon after that. Normal newborn foals suckle about seven times an hour. They are alert and active, then suddenly lie down and fall asleep for about 20 minutes before getting up again and nursing or playing.
Weakness and lethargy
A normal foal, when asleep, will wake up quickly and stand, ready to flee, if disturbed. Not so with a foal that is suffering from sleepy foal disease. It looks tired and, when it lies down to sleep, is reluctant to stand up. The ears droop and the posture is relaxed. The alert, nervous, excitable look that is normal for a young foal is absent.
The foal shows progressive increase in weakness and looks more and more lethargic or sleepy. The sucking reflex may decline and the mare will appear restless as her udder fills with milk. Sometimes the foal appears to be suckling but when it ducks away from the mother afterwards, it dribbles milk and has a “milky face” – the mare has let down her milk and it has squirted on to the lips and face of the foal instead of being swallowed.
Often, the first foal born after the mare is infected shows the most severe symptoms. Later, it seems to have a partial immunity and shows symptoms only two to three weeks after being born.
The foal can have pneumonia, joint infections or an inflamed, infected umbilical cord. The pneumonia results in a slow, soft cough, while joint infections cause gradually increasing lameness in one or more joints.
Foals with lung infections also tend to gradually lose interest in their surroundings and become sleepy. The bacteria spreads from the lungs into the system and tiny abscesses develop in all the major organs, particularly the kidneys.
As the disease progresses, the foals also stop sucking and lie down for longer and longer periods. Without rapid recognition of the disease and treatment with appropriate antibiotics, these foals will die within a week or two.
Joint infection
The other symptom complex seen with sleepy foal disease is related to infection of the joints and often the umbilicus. Previously it was thought that this infection resulted from the umbilical cord not being disinfected at birth. However, it has since been shown that it also arises from infection by the mare. Recently, A. arthitidis, a closely related species, has also been isolated from foals showing septic joints soon after birth. There are several other bacteria, including strangles (Streptococcus equi), that also cause septic joint infections in young foals.
It spreads slowly
Generally speaking, sleepy foal disease does not infect a whole herd of horses at the same time. It spreads slowly and may follow the introduction of a new broodmare. Initial cases may show as sporadic abortions or weak foals or there may be increasing numbers of foals with pneumonia and joint infections. It is important to always send foals that are born dead, aborted or die within the first few weeks of life for necropsy. Large equine veterinary practices can be contacted to discuss details.
In general, a fresh carcass and aborted material should be put into plastic bags and kept cool. A postmortem should be performed as soon as possible, preferably within two to four hours after death.
Getting rid of the disease in a large stud of breeding mares can be problematic unless the breeder works closely with a veterinarian.
E-mail Dr Mac c/o [email protected]. |fw
