Neonatal isoerythrolysis is caused by an incompatibility between blood groups of the mare and foal. Antibodies to the foal's red blood cells are formed by the mare and secreted in her colostrum. When the foal nurses and absorbs these antibodies, its red blood cells are destroyed. Without prompt veterinary treatment, the foal becomes anemic and dies.
For more information, see Care of the Newborn Foal.
