Fading Kitten Syndrome

Seeing a litter of kittens fade away is extremely distressing. Understand the causes of fading kitten syndrome, including blood group incompatibility.

Fading kitten syndrome is an umbrella term for a number of conditions that cause part of a litter or an entire litter of kittens to quite literally fade. They gradually become weaker and less vibrant and ultimately, if the cause is not addressed quickly, they die. This usually happens within the first week of life. Fortunately, once you understand the common causes of fading kitten syndrome, you can work to minimise the risks.  One of the main causes of fading kitten syndrome is feline neonatal isoerythrolysis, or blood group incompatibility, and this is dealt with towards the end of this article. 

Causes of Fading Kitten Syndrome

There are a wide range of causes of fading kitten syndrome. Many of these causes are easily preventable, so with a little research and preparation, you can avoid them entirely. 

1. Fading kittens syndrome from poor hygiene:

hygiene and fading kitten syndrome

  • Kittens have low immune systems so poor hygiene can create conditions that easily overwhelm them 
  • To give your kittens the best possible chance of survival, make sure that change your queen's litter tray daily, and disinfect it with a good anti-viral solution that is safe for use with cats. You can read about litter tray cleaning options here
  • Wash your queen's bedding daily, before and after the kittens arrive. Replace it with clean bedding each day. Wash the bedding on a 60 degree wash cycle to kill viruses. Use a non-bio laundry liquid to avoid irritating the kitten's delicate skin, and make sure you use an extra rinse cycle to ensure the laundry liquid is properly removed
  • Keep the area that your queen is in clean and free from dirt
  • Change her food and water bowls daily, putting down clean sterilised bowls each day. 
  • This will help prevent the build up of bacteria and spread of viruses. 

2. Fading kittens syndrome from hypoglaecemia:

  • if a kitten does not get enough food, regularly enough, its blood sugar levels will become dangerously low, and can result in death. 

  • Keep watch over your kittens and ensure that they are all feeding regularly. 

  • Weigh them at the same time every day to make sue that they are all gaining weight. 

  • If needed, use kitten milk replacement to support the kittens if they are struggling

  • Check your queen's nipples daily to make sure she does not have mastitis

3. Fading kittens syndrome from hyperthermia:

  • Newborn kittens are unable to regulate their own body temperature
  • If they get too hot, or too cold, it can be fatal
  • Kittens rely on their mother's body to keep them warm.
  • Using a heat pad and keeping a room thermometer in the kittening room can help to ensure they are kept at the correct temperature 

4. Fading kittens syndrome from infections

  • bacterial infection, viral infection and, parasitic infection can be very serious to newborn kittens
  • make sure that your queen is healthy before she becomes pregnant
  • if you are using  a stud boy from another breeder, make sure that they have very high standards of cleanliness. Check that he is not an 'open stud' who is advertised online, as these stud boys pose extremely high risks of contagious infections
  • keep your hygiene standards exceptional throughout your household, not just with your pregnant queen
  • make sure your pregnant queen and her kittens do not have any contact with any other cats in your household 
  • read more about Feline Coronavirus 
  • read more about FIP

5. Feline Neonatal Isoerythrolysis, or blood group incompatibility

Feline Neonatal Isoerythrolysis (FNI) is a very serious, but completely avoidable condition that can arise in newborn kittens, and it is almost always fatal. The symptoms of the condition are very distressing, with the tips of the kittens' bodies necrotising before they pass away. Any time that kittens fade away or die is referred to as fading kitten syndrome, and this is included in that term.

It occurs when two parents of incompatible blood type are bred together.

Some cats have Type A blood, some have Type B and there is a third very rare blood type of AB. Type A blood cats can either be homozygous for A (AA blood) or heterozygous and carry a recessive B allele (Ab). The B allele is recessive to the A allele. 

Therefore, depending on which blood types the parents have, the kittens will have various combinations of A and alleles. Some breeds do not have type B blood, and in others the prevalence of it is very low. In British Shorthair cats around 60% of cats are thought to have type B blood, so understanding blood group incompatibility is the first step any aspiring breeder should take. If you learn to understand it early on, it will help you make informed decisions when choosing your cats. 

The problem arises because type B blood has a very high titer for anti-A antibodies, and when this is passed to the kittens in the colostrum, during the first 24 hours or so of a kitten nursing, the kittens will receive very high levels of those anti-A antibodies. This means that if she has a kitten with blood group A, the cells in her colostrum will enter the kittens and will attack their red blood cells, essentially killing them.

Type A blood does have some anti-B antibodies, but usually the number is so small that Feline Neonatal Isoerythrolysis, or fading kitten syndrome, is unlikely.

The rare type AB blood, which is a third type and is unique from type A and type B, is a less well understood blood type and will not be dealt with in detail here

Here is a basic summary of feline blood group matings:

  • Where a blood type BB queen is bred to a blood type BB stud, there is no problem


  • Where a blood type AA queen is bred to a blood type AA stud, there is no problem


  • Where a blood type BB queen is bred to a blood type AA stud, all of the kittens will be blood type AB (A carrying B) and therefore all of them will be at high risk of Feline Neonatal Isoerythrolysis


  • Where a blood type BB queen is bred to a blood type Ab stud, half of the kittens should be blood type BB and half of them should be blood Type Ab. Therefore half them will be at high risk of Feline Neonatal Isoerythrolysis


  • Where a blood type Ab queen is bred to a blood type BB stud, then all of the kittens will be blood type Ab or BB. The BB kittens may be at a moderate risk of Feline Neonatal Isoerythrolysis and this risk will increase as the queen has more litters with kittens of blood type BB in them


  • Blood group AB is a third blood group, separate from blood groups AA, BB or Ab. It is not yet fully understood and has not been dealt with in this article. 

How to avoid Feline Neonatal Isoerythrolysis

Feline Neonatal Isoerythrolysis, which causes fading kitten syndrome, can be avoided altogether by blood grouping any cat that you want to breed from before you plan the mating. Blood grouping can be done by your vet, or by a DNA swab by Langford Vets which you can order online here.

In order to eliminate the risk it is recommended to only breed blood group BB queens to blood group BB studs, and blood group Ab queens to blood group AA studs. Blood group AA queens may be bred to blood group BB studs, AA studs or AB studs, as all of the offspring will still be blood group A or Ab, and there will be no risk to the kittens.  

It is generally, but not universally, accepted that a blood group A queen, whether or not she carries a b gene, may be put to a blood group B stud without significant risk, because of the lower antibody titer level amongst blood group A queens. However, it is thought that over time, the queen's titer level will increase and could lead to kittens being at risk of neonatal isoerythrolysis.

If you find that you have a mating that will result in incompatible blood groupings, leading to fading kitten syndrome, then act immediately - confirm the blood groups of the cats and if there is any risk at all, remove the kittens from the queen as they are born, before they get a chance to suckle any milk at all. Feed them every hour or two with a good quality kitten milk replacement (KMR) After 24 hours the risk will have passed and they can be given back to their mother to suckle.

Read more about Feline Blood groups