Haemolytic Disease in Newborn Foals
Equine Veterinarian and Consultant Nutritionist Blood-typing of mares and stallions to confirm parentage offers owners an early warning system for detection of foals at risk from potentially fatal jaundice. Jaundice or haemolytic disease occurs naturally only in humans and horses and is due to the mare and stallion having different blood groups. It is commonly associated with the blood types Aa-negative and Qa-negative. Most stallions are Qa-positive and if the mare is Qa-negative or Aa-negative, she produces antibodies to the Qa-positive red cells. The antibodies attach to the foal’s red blood cells. The antibodies flag the red cells for destruction and removal from the circulation.
In the horse, antibodies cannot cross the placenta. The foal is safe from the antibodies until it is born. Human babies, on the other hand become affected before they are born, because in people, antibodies cross the placenta and pass into the baby, causing destruction of the red cells.
Ordinarily, it is critical for foals to receive colostrum, to load up with antibodies to protect them for 3 to 4 months until they are old enough to produce their own. However, if the mare is a different blood group to the foal, the colostrum becomes a lethal cocktail. Anti-red cell antibodies concentrate in the colostrum and when the foal begins to nurse, the antibodies enter the foal’s circulation and attach to the red blood cells. Then begins is a continuing process of red blood cell destruction causing profound anaemia, jaundice, weakness and death.
Diseases and conditions that affect newborn foals are grouped into various categories, but the clinical signs are often the same and anything outside ‘normal’ is a cause for closer observation and prompt veterinary advice. Newborn foals should be closely observed for the first few days and any subtle changes in behaviour must be investigated promptly. Some foals may be ‘normal’ at birth but close observation will reveal slight changes which are not specific for any particular disease or infection, but Published date: 11-2006 that indicate a need for veterinary examination. A characteristic of most diseases is sleepiness and lethargy. All foals sleep most of the time, so it is important to note any foals that seem unusually sleepy. Some foals fall asleep while standing and may fall down if they go into a deep sleep. The complicated maneouvring of legs required to lie down is usually achieved after the first