Overview
Neonatal isoerythrolysis in kittens causes a litter to become weak and die within days of being born. While death of the newborns can be caused by infectious diseases, birth defects, and a plethora of other factors, in the case of neonatal isoerythrolysis it is a result of mismatched blood types and can be completely preventable.

Blood groups in cats work in similar ways as humans, in that blood types are determined by the type of antibodies present in an individual’s blood. Feline blood groups include type A, B, and AB (while the names are similar, they are different from the human ABO blood groups). Mismatched blood types between a mother and the unborn litter do not present any problems since the antibodies do not cross the placenta. However, shortly after birth, the kittens will receive all the mother’s antibodies via colostrum (first milk). The mother’s mismatched antibodies will result in the destruction of the kittens’ red blood cells, causing severe anemia and eventually death.

While an overwhelming percentage of cats in North America are of a single blood type (type A), different breeds can have a different distribution in blood groups. Neonatal isoerythrolysis can result in repeat loss of kittens, and can be a devastating condition especially for cat breeders. However, it is easily prevented by determining the blood types of cats prior to breeding, and by preventing the kitten from receiving their mother’s colostrums if their blood types mismatch.

Symptoms and Diagnosis

The newborn kitten will appear pale, weak, and jaundiced. Their urine may be tainted brown, and in less severe cases the tail tip might become necrotic. Most kittens affected by neonatal isoerythrolysis will die within 48 hours.

Positive diagnosis can be done by blood typing both the mother and the kittens; neonatal isoerythrolysis is only possible when the mother is type B and the kittens are type A or AB.

Treatment
Blood transfusion and supportive care are possible for the affected kittens, however most do not survive. Prevention is the most effective way to avoid losing newborn kittens through neonatal isoerythrolysis. In an active breeding program, type B females should only be bred to type B males to eliminate the chance for her to carry type A or AB kittens. If a type B female is already pregnant, and it is likely that the litter contains type A or AB kittens, the newborn kittens should be prevented from receiving the colostrum produced in the first 48 hours after birth. Plasma transfusion can be given to the kittens later on to supplement them with necessary antibodies. After 48 hours the mother starts to produce regular milk, and the kittens can nurse normally thereafter.