Blood Group of Breeding Cats

Some breeders may not be aware of the implications of the blood group or blood types of their breeding cats.  The blood group has no effect at all on a pet cat, but it is important knowledge to have with respect to your breeding cats.

There are three blood groups is cats.  There is blood group A, blood group B and blood group AB (rare).  Blood group A is a dominant type and blood group B is recessive.  Each cat gets one gene for blood group from its sire and one from its dam.  In order for a cat to be blood group B, it must receive a blood group b gene from each of its parents.  If a cat gets a blood group A gene from one parent and a blood group b gene from the other parent, because the A gene is dominant, the cat’s blood group will be A.



















The chart below gives a good explanation of how the blood type genes work.





Why is blood group/type important in breeding cats?  The red blood cells of cats are made of proteins and these proteins are different in a blood type A cat and a blood type B cat.  In blood type B queens, they produce strong antibodies that attack the red blood cells of any blood type A kittens.  This immune system attack by the queen only occurs during the time she is producing colostrum (the first ~ 3 days after birth).  Although blood type A queens also produce antibodies against blood type B kittens, these antibodies are not strong and do not cause harm to the kitten. 




If a type B queen is bred to a type A sire, and the kittens are permitted to nurse during the period the queen is producing colostrum, a condition known as neonatal isoerythrolysis will occur as a result of the queen’s antibodies destroying the red blood cells of any kittens that are blood type A.  Some symptoms include kittens that are no longer nursing, weakness and general failure to thrive.  Other signs include jaundice and dark urine.  In some cases, the tail tip drops off.  However, it is important to note that not every case of neonatal isoerythrolysis will result in jaundice and the kittens may simply fail to thrive and die.  Only the blood type A kittens will be affected.  In the photos below, you can see the jaundice in the color of the noses of the kittens, as well as the bloody tip of a tail.  The paw in the photo below shows the yellowing of jaundice.








If you are planning to breed a blood type B queen to a blood type A sire, you must ensure that the kittens do not suckle at all from the queen for three days.  You can either put them with another blood type A queen you have that is lactating and will accept them, or you can hand raise the kittens for the first three days.  You can make a garment for the queen so that she can still clean and cuddle her kittens, but you must be sure that it covers all nipples and there is no way for a kitten to slip through to nurse.  The issue with this is that the kittens will not receive the beneficial colostrum they would get by nursing the first few days after birth.


As a RagaMuffin breeder, you should be aware that the B blood type does exist in our breed and it is known to be in at least a few lines.  Since most breeders do not test their cats for blood type, it is difficult to determine the prevalence in our breed, though it is not likely highly prevalent.  However, it is possible that unexplained kittens fading and dying could be due to neonatal isoerythrolysis.


It is now possible to send buccal swabs to UC Davis to genetically test for the cat’s blood group.  This will not only tell you the blood group but in the case of a blood group A cat, it will tell you if the cat carries the gene for B blood type.  Visit for information on blood type testing.

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