Alloimmune haemolytic anaemia of the newborn
An alloantigen is an antigen existing in alternative (allelic) forms in a species, thus inducing an immune response when one for is transferred to members of the same species who lack it. So alloimmune haemolytic anaemia occurs when a neonate inherits the sire's blood type and drinks colostrum from the dam, which contains antibodies against the sire and thus the neonate's red blood cells.
It can naturally occur in humans (Rhesus disease) and foals (neonatal isoerytholysis) and can be induced in pigs and cattle by vaccines containing allotypic red blood cell antigens.
Neonatal Isoerytholysis (NI)
Occurs in some foals, and always occurs in mules due to the incompatibility of the sire and dams blood types.
First pregnancy from a stallion with incompatible blood type to the mare:
- Mare is mated with a stallion with an incompatible blood type.
- The neonate may inherit the sire's blood type.
- At parturition, or because of placentitis, RBCs from the foal enter the maternal circulation.
- The surface of the foal's RBCs possess an antigen (usually Aa or Qa) that the mare's RBCs lack.
- The mare begins to mount an immune response towards the foal's RBCs.
- There are no antibodies against the foal's RBCs in the mare's colostrum as there has not been sufficient time to mount an immune attack and secrete them into the colostrum.
- The foal's intestine stops absorbing maternal antibodies after 30 hours (as previously discussed) and thus, when the alloantibody is secreted in the milk, it does not affect the foal.
Subsequent pregnancy from the same stallion or same blood group as previously exposed to
- Foal is born and suckles from the mare.
- Colostrum already contains alloantibodies against the foal's RBCs causing there to be RBC destruction or removal from the circulation (type II hypersensitivity reaction) leading to haemolytic anaemia and jaundice.
- When the foal's intestines are no longer able to absorb maternal antibody (approximately 30 hours post partum) it is safe to return the foal to the mare.
Almost all mule pregnancies result in NI due to the mare lacking a factor called donkey factor.
References
Books
A.H. Andrewa Bovine Medicine - Diseases and Husbandry of Cattle Blackwell Publishing 2004 2nd Edition
Koterba, Drummound and Kosch Equine Clinical Neonatology Williams and Wilkins 1990
P. Lydyard, A. Whelan and M.W. Fanger Immunology Garland Science 2nd Edition 2004
Websites
www.sheepandgoat.com