Fading kitten syndrome

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). Although always a worry, birth defects are a relatively uncommon cause of fading kittens. 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).

©Emrah Ayvali / Pexels

The definition of fading kitten syndrome varies but the most widely accepted is kittens fading before they are weaned which usually occurs at 7-8 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. This is a useful division because likely cause of FKS is different between these groups

Perinatal deaths are most commonly associated with difficulties during the birthing process or severe genetic or developmental abnormalities.

Neonatal deaths are most closely associated with low birth weights (less than 75 g), 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.

Young kittens have limited ways that they can show illness so what is 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.

There are many potential causes of FKS:

• Maternal factors such as illness during pregnancy, difficulty giving birth (dystocia), mastitis and trauma.
• Congenital defects may account for 10-20% of deaths these are both kittens with genetic abnormalities and those whose development in utero has gone wrong due to non-genetic factors such as illness or malnutrition of the queen.
• 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 10-15 g/day over the first 1-2 weeks.
• Neonatal isoerythrolysis occurs when the blood group of the queen and kitten is incompatible leading to antibodies in the queen’s milk destroying the kitten’s red blood cells.
• 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 fight 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 antibiotics being of limited value.

Breeding queens should be in good health, free of parasites, and vaccinated. Avoid overcrowding and breeding from queens with poor mothering instincts or those that have had a prolonged labor in previous births. Ensure the queen and tom have compatible blood types.

Encourage early bonding and make sure that colostrum (the mother’s first milk) is the first feed as this provides antibodies and transfer of immunity.

The kittens should be kept at a constant, warm temperature and monitored carefully, including being weighed daily in the first 1-2 weeks. Good hygiene must be maintained and over-crowding (eg multiple queens with coinciding litters) should be avoided. The kittens should not be handled excessively so as not to stress the queen.

Lack of weight gain is a significant warning sign with these kittens being closely watched, given opportunities to suckle and kept warm.

Your veterinarian will check kittens for congenital problems and signs suggesting specific infections requiring treatment. Your veterinarian may recommend that the kittens be taken into the hospital and fed with an orogastric tube that is placed for each feed. Older kittens may have a feeding tube placed in the esophagus (gullet), fitted under anesthetic. Oxygen therapy may be given along with fluid therapy, antibiotics, and colostrum (mother’s first milk). Temperature and bodyweight will be monitored until the kitten is bright, eating and gaining weight.

Unfortunately, as a significant number of causes such as genetic defects or viral disease are not directly treatable many kittens with FKS are unlikely to survive with deterioration being very rapid in some cases. Chances of success can be maximized by spotting and intervening early. If a kitten does die then serious consideration should be given as to whether a post-mortem is carried out as this may provide important and valuable information if other kittens in the litter start to fade. A diagnosis of the cause of death is found in around two thirds of FKS at post-mortem.