There can be few events as distressing for a cat breeder as watching a litter of kittens fade and die within the first 48 hours of life. Yet this has been the experience of many British Shorthair breeders until it was recognised that the reason was that the queen had a different blood type from her kittens and was killing them, unintentionally, through her milk. It is particularly a problem in the British breeds, as almost 60% are blood group B, but it can affect almost any breed of cat, including our dear old domestic moggies.

Knowing your cat’s blood group can save their and their kittens’ lives.

What are feline blood groups or blood types?
Our blood consists of red blood cells, white blood cells and plasma. The red cells carry oxygen and their well-being is essential for life. Red blood cells, like most other components of the body, are made of protein, and proteins can be recognised and destroyed by the body’s immune system. The cat has essentially two blood groups: A and B (although there is a third, very rare, group, AB, which is a combination of the two). The red blood cell proteins are A in one group, B in the other (see figure 1). In fact, the proteins on the surface of type A and B red blood cells are only slightly different, but of course the immune system can detect the difference.  

As you know, if you have a blood transfusion, it is essential to get the right type of blood, a transfusion of the wrong blood type could kill you – it is no different for cats. The immune system of the cat or person receiving the blood transfusion reacts to the blood which it sees as alien, and the consequences can be fatal.

What is neonatal isoerythrolysis?
A recently recognised cause of fading kittens in pedigree cats is neonatal isoerythrolysis, where kittens have a different blood type from their queen, and, on suckling her milk, receive antibodies against their own red blood cells. The antibodies cause destruction of the kittens red blood cells which leads to jaundice (see figures 2 and 3), brown urine, and rapid death. In less severe cases, the tail tip drops off.  

Samples of blood from the kittens and queen can be blood typed to confirm the diagnosis.  

 
Figure 2.  A litter of kittens with neonatal isoerythrolysis.  Note the
jaundiced (yellow) noses and bloody tip of the tail of the white kitten. 

Figure 3.The paw of a kitten with neonatal isoerythrolysis – note how jaundiced (yellow) it looks.

Prevention of neonatal isoerythrolysis

1. Typing the queen and tom before mating
Prevention involves blood typing the queen and any prospective tom that she may be mated with. Cats get one gene for blood type from their mother (in the egg) and one from their father (in the sperm). The genes for blood type A are dominant to the genes for blood type B, which means that a cat with a mixture of genes – Ab (note that this is different from the third, rare, blood group AB) – will have blood type A  A blood group B queen can give birth to a blood type A kitten if mated to a blood type A tom carrying the genes for blood type B, (as in figure 4 and table 1). This is the situation in which neonatal isoerythrolysis is most likely to occur.

Figure 4 - How two type A cats can give birth to a type B kitten

Table 1 - What happens when you mate a blood group B queen to a blood group A tom cat depends on whether his genes are purely A or a mixture of A and B. The kitten’s genes are represented by the shaded boxes. The biggest risk of neonatal isoerythrolysis is when kittens with blood type A are born to blood type B queens.

Cats with blood type B are recessive (i.e. they all have two b genes, genotype bb) and can be safely mated to other blood type B cats - all the kittens will be blood type B (table 2.) and neonatal isoerythrolysis will not occur.

KEY

Table 2. - What happens when you mate two blood group B cats together.

Table 2                   

All of the kittens will be blood group B (shaded area represents kittens of such a mating) and there will be no risk of neonatal isoerythrolysis.

 Table 3. - What happens when you mate two cats with blood type A together.

In the simplest scenario, all the genes of the tom and queen code for blood type A and all the kittens will be blood group A. However, since blood group A is dominant to blood group B, one or both cats could be carrying the gene for blood group B.

In the first example above, the tom has both versions of his gene (i.e. the one from his mother and the one from his father) coding for blood group A, therefore all his kittens will be blood type A. Half of his kittens will carry the gene for blood group B, which they have gotten from their queen. None of the kittens will be at risk of neonatal isoerythrolysis as they all have the same blood group as their queen.

In the second table both blood group A cats are carriers of the gene for blood group B. As you can see, one quarter of the kittens born to this pair will be blood group B (blue shaded box). Queens with blood group A have less anti-type B antibody than blood group B queens have anti-group A antibody, so the type B kittens of this mating might survive. However, if the mating is repeated, the queen will build up anti-B antibody and eventually one fourth of her kittens could die of neonatal isoerythrolysis.

The only way to establish the genotype of a blood type A cat is by trial mating with a type B cat.

Table 4.- The outcome of trial matings to establish whether a blood group A tom carries blood group B genes.

Table 5. - The outcome of trial matings to establish whether a blood group A queen carries blood group B genes.

Does Neonatal Isoerythrolysis occur in my breed?

At the University of Glasgow, we are collecting data for the frequency of type B cats in the UK pedigree population (see table 6). Type AB is very rare. Remember that some breeds are relatively uncommon and not many cats have yet been tested, so that the figures given in this table are based on a small sample size and may not be wholly accurate. If you have had any kitten deaths which could be due to neonatal isoerythrolysis, have your queen tested no matter what breed she is.

Table 6.  Blood type B frequencies in various feline breeds: breeds without type B cats are safe from developing neonatal isoerythrolysis.  

 
* Where I have not tested any members of a breed, or another author has tested more cats, I’ve used their percentages: Knottenbelt et al, 19991 or Callan & Giger, 19942.

2. Blood group testing the kittens at birth
A drop of blood from the umbilicus of the newborn kitten can be used to blood type the kitten to assess whether it is at risk from suckling. Clearly the blood type of the queen must also be determined. It is safe for a kitten to suckle a queen of the same blood group, but if the kitten's and queen's blood types differ, you may want to prevent the kitten from suckling their queen for the first 16 hours of life.

3. Prevent at-risk kittens from suckling their queens for 16 hours
The gut of the newborn kitten only remains permeable to antibodies in colostrum for the first 16 hours of life, after which time it is quite safe for the kitten to suckle its mother, even though she is a different blood type.  

Further reading
1. Knottenbelt CM,Addie DD, Jay MJ, Mackin AJ. 1999 Determination of the prevalence of feline blood types in the UK.   Journal of Small Animal Practice 40 115-118

2. Callan, MB, Giger U. 1994 Transfusion medicine. Consultations in feline medicine 2.  Ed. August, JR. 525-532

3. Casal ML, Giger U. 1997 Colostrum: friend or foe? Feline Advisory Bureau Journal 35 70-72

Help neonatal isoerythrolysis research

If you have any experience of mating type A queens to B toms, or type AB cats to any type (A, B or AB), I’d love to hear from you.  Please fill out this email form: (to be added soon - please come back and fill it out!)

Updated 7/Jan/03

Site ©2000 Dr. Diane Addie
Site Design © Melody Amundson, Mariposa Creations