• Fading kitten syndrome (FKS) is a catch all term that is used to describe pre-weaned kittens that stop growing and gradually decline over a short period usually hours to a few days. FKS can affect individual kittens within a litter, part or the whole of the litter. FKS can be a one off event or be an ongoing problem in a breeding colony.
• In pedigree cats around 8.5% of kittens are stillborn and a similar percentage die before weaning. There is considerable variation between cat breeds with most of the common breeds showing pre-weaning mortality rates between 5 and 12%. Recent figures for domestic shorthair (DSH) cats are not available but limited information suggests that FKS is less common when compared to pedigree cats although in shelter and rescue facilities death rates are higher at around one in eight kittens.
• The definition of fading kitten syndrome varies between authors. Some would only include kittens <2 weeks old. More commonly FKS covers from birth to weaning (around 8 weeks of age). This group is often subdivided into perinatal (within the first 24 hours) neonatal kittens (1-14 days old) and pre-weaning kittens that are over 2 weeks old.
• Cause:
  • Perinatal deaths are most commonly associated with difficulties during the birthing process associated with hypoxia and trauma or severe genetic or developmental abnormalities.
  • Neonatal deaths are most closely associated with low birth weights (less than 75g), trauma (usually caused by the queen), single kittens, litters of over 7 kittens and blood group incompatibility with the queen (neonatal isoerythrolysis). Low birth weights likely reflect problems during a kitten’s development in utero that may or may not be genetic. Neonatal death rates also seem to be higher in younger (especially first litter) and smaller queens. Mortality rates increase after a queen’s fifth litter with congenital defects becoming more common.
  • Preweaning deaths are more likely to be infectious in nature with viral disease especially feline parvovirus being more common than bacterial infections.
  • Maternal factors such as illness during pregnancy, difficulty giving birth (dystocia), agalactia, mastitis and trauma.
  • Congenital defects may account for 10-20% of deaths these are both kittens with genetic abnormalities and those that have suffered abnormal development in utero due to non-genetic factors such as illness or malnutrition of the queen. Some conditions, such as cleft palate, can be associated with a genetic abnormality or caused by abnormal in utero development. In litters with more than one affected individual, genetic abnormalities tend to cause the same defect and will only affect a proportion of the litter (very rarely more than 50% of the litter and usually less than 25%). An insult during in utero development tends to result in most kittens being affected but the abnormalities being different as kittens will be at a slightly different stage of their development at a specific time point.
  • Low birth weight is the single highest risk factor for neonatal death. Kittens typically lose <10% of their bodyweight in the first day and then gain 10-15g/day over the first 1-2 weeks. Low birth weight is generally defined as >25% less than average for the breed. Such kittens tend to have decreased nursing ability and are more prone to hypoglycemia, hypothermia and sepsis.
  • Neonatal isoerythrolysis occurs when the queen’s blood group and the kitten’s are incompatible as preformed antibodies in the queen’s milk results in immune destruction of the kitten’s red cells. This most commonly occurs with a group A kittens from a mating of a group A stud cat with a group B queen.
  • Infectious disease tends to be responsible for FKS in older kittens with viral causes such as parvovirus, herpes and calicivirus being more common than bacterial, parasitic or protozoal disease. Kittens have limited ability to respond to infection as their immune system is immature relying on immunity that is passed to them by the queen in the first milk (colostrum). Sadly as many infections are viral, specific treatment is not possible with antimicrobials being of limited value.
  • Environmental causes: most commonly poor hygiene, inadequate nutrition and dehydration. Extremes of temperature and toxin ingestion are relatively uncommon causes.
• Signs: the younger a kitten is the fewer the number of specific signs that tend to be seen. Most commonly seen is a kitten that is not suckling well and whose weight plateaus and then starts to fall. Initially these kittens will vocalize but after a while will become quiet, lethargic and often separated from the rest of the litter. Temperature tends to be low and diarrhea is relatively common.
• Diagnosis: a complete investigation including history, examination, laboratory tests and, sometimes, post-mortem examination. Post-mortem should be recommended as it may give valuable information as to cause and potential treatment should other kittens start to fade.
• Treatment: symptomatic management and nursing care. Successful treatment will depend on:
  • Accurate identification of cause.
  • Maintaining nutrition.
  • Appropriate treatment.
• Prognosis:
  • Generally guarded - the majority of fading kittens do not survive. Likelihood of survival is maximized by the breeder spotting fading kittens as early as possible and the veterinary team establishing cause.
  • Lack of weight gain is a significant early warning sign, such kittens should be closely watched, given opportunities to suckle and kept warm. If failure to gain weight or weight loss occurs for >24 hours advice should be sort form the veterinary team.

Presenting signs

• A kitten failing to gain or losing weight.
• Kittens that are quiet or inactive.
• Kittens separated from the rest of the litter.
• Failure to take milk.
• Maternal neglect.
• Kitten developing diarrhea.

Acute presentation

• Kittens found dead.
• Rapid weight loss, inactivity and failure to suckle.

Age predisposition

• Perinatal, neonatal or preweaning.

Cost considerations

• A full investigation of disease of young kittens often is not thought cost effective for individuals especially commercial breeders. If a kitten has died, then post-mortem Post-mortem technique can be the most cost effective way to establish a retrospective diagnosis that can be used to help other kittens in the litter should they become sick or inform future breeding practices.
• Because owners are less likely to be emotionally involved with the kitten, they are less likely to fund expensive investigations and treatments.
• Many kittens can be helped with relatively little expense by history taking, examination and minimal laboratory tests. Key factors to success can be to ensure appropriate nutrition (by encouraging suckling, bottle or tube feeding and hydration and maintain an appropriate body temperature.
• A breeder with repeated problems may need to spend more money. Post-mortem examination with histopathology and microbiology are cost effective. Best results are obtained from a sacrificed moribund kitten that has not had antibiotics.

Special risks

• Fading kittens are poor anesthetic risks.
• Drug dose rates for kittens poorly established - in general they have a high body surface area to weight ratio, but poor excretory ability so often relatively high doses need to be given but less frequently.