Fading Kitten Syndrome, aka FKS, is not a disease. It is a collection of symptoms, the very first of which might be the unexplained death of a very young kitten. In that respect, it has been compared to SIDS (Sudden Infant Death Syndrome) in human babies.
With kittens, however, an extremely perceptive caregiver might be attuned to the symptoms, and sometimes take actions to prevent immediate death, and depending upon the causes, allow the kitten to survive indefinitely.
People who rescue and foster pregnant cats and/or the fostering of kittens are especially qualified to spot the symptoms, as the offspring of stray and feral cats are particularly prone to this condition. In fact, many people involved in rescue believe in the spaying of rescued pregnant cats for exactly this reason. Because spaying a pregnant cat is technically "surgical abortion," One veterinarian even refers to it as "Feline abortion: often an unnerving necessity."
The first six to eight weeks of kittenhood are the most serious for the possibility of Fading Kitten Syndrome (some experts use 12 weeks as a guideline).
Symptoms of Fading Kitten Syndrome can include:
Extremely Low Birth Weight
The kitten is usually the "runt of the litter," much smaller and less active than its littermates.
Unable to Nurse Properly
Healthy kittens are able to nurse almost immediately after birth. The "fader" kitten might be described as the "hind teat kitten," and it often is not strong enough to grasp and suckle the mother cat's nipple.
During first 72 hours or so, the fluid is colostrum, a special milk which provides nutrients and also whatever antibodies the mother cat may have acquired, giving the kitten what is referred to as "Passive Immunity". Several companies are now manufacturing colostrum for kittens, such as Just Born Milk Replacer Plus Colostrum.
Abandonment by the Mother Cat
Queens have an instinct about their litters, and will often abandon the weakest kitten. A vivid but sad example of "survival of the fittest."
Since newborn kittens don't yet have the means to regulate their own body temperatures, they depend on their mom for warmth. If the mother cat has abandoned a kitten, the kitten will quickly develop hypothermia. The hypothermic kitten will be lethargic, and its mouth and gums will be a bluish shade rather than a healthy pink. Death will likely occur soon thereafter, unless human intervention occurs, with the provision of a warm nest and food supplementation.
Causes of Fading Kitten Syndrome
There are a number of causes of FKS, and any potential treatment will greatly depend on the cause or causes. Some of the most common ones include:
Disease or Malnutrition of the Mother Cat During Gestation
If this is the first litter of the queen during the current "kitten season," she may have enough food to allow proper development of the embryos into viable kittens. However, since a whole female cat can conceivably give birth to up to five litters of kittens within a year, it's easy to see how she could become malnourished and sick by the end of the year.
Lack of adequate nutrition will weaken her, making her more susceptible to disease. This combination deals a "double whammy" to the later litters, resulting in both stillborn kittens, kittens born with disabilities and kittens with FKS.
For these reasons alone, it is imperative to take a suspected pet pregnant cat to the veterinarian for a prenatal checkup, and to ensure that she can even carry to full term, discuss her diet (canned kitten food would be preferable), discuss the advisability of vaccinating her with core vaccines, and also to discuss the possibility of spaying her.
There are a number of infectious diseases which can quickly take out a whole litter of kittens. For this reason alone, it is important to keep the litters of a stray or feral queen completely separated from the household cats and to use scrupulous sterilization methods to prevent your carrying these infections to your own cats.
Fleas and Other Parasites
Infestations of fleas feasting on a kitten can quickly cause anemia or even Hemobartonella, both potentially fatal to a young kitten.