Kittens suddenly die for a multitude of reasons. As someone said, they are fragile creatures. Some kittens are “predetermined to fail the test of survival because of low birthweight and influences that affect growth and development in the uterus”. In short, some kittens simply are unviable in terms of survival which may account for the reason why domestic cats are such good breeders.
There appear to be two main headings as to why kittens suddenly die: fading Kitten syndrome and kitten mortality complex. To these you can add the usual diseases.
Fading kitten syndrome
During the first two weeks of life newborn kittens are most at risk of dying. They may have acquired diseases in utero and birth injuries during delivery and labour. These may cause death. Other causes under this heading may include a failure to provide adequate heat where the kitten is born and a failure to provide a proper diet with sufficient calories and nutrients including taurine. On that last point, by the way, there is a post on the Quora.com website in which the owner of a kitten said that they fed their cat with “frozen fish pieces “. They were asking why their cat died suddenly. A lot of people said that the diet caused it. They were criticised by a PhD graduate who said that there were other reasons. But just feeding fish would produce a lack of taurine which in turn would kill the kitten in time.
Some kittens are “developmentally immature”. They lack sufficient birth weight and muscle mass and subcutaneous fat. They may fail to breathe deeply and nurse effectively. They may struggle to maintain body warmth. If the birthweight is 25% below that of their siblings they may be crowded out by them and forced to suckle at a less productive nipple. These kittens fail to nurse properly. They become dehydrated and chilled. They may develop a “shock like state due to circulatory failure”. The temperature drops as does the heart rate and breathing. The body temperature drops below 94°F and vital functions become depressed. They eventually fall into a coma combined with breathless periods lasting up to a minute. The condition becomes irreversible and they die.
Kitten mortality complex
At one time it was believed that this was caused by a single virus, the same one that causes feline infectious peritonitis (FIP). Is now considered to be a spectrum of illnesses which affect newborn kittens in the first weeks of their life. Kittens in the first stages of their life are at risk of neonatal illnesses including septicaemia, toxic milk syndrome, umbilical infections, feline infectious peritonitis, panleukopenia and isoerythrolysis (the mother has antibodies against the blood type of the newborn). They can cause death. But they cause death less often than trauma during birth and an inadequate supply of milk from the mother. In addition kittens can suffer from external and internal parasites, low blood sugar, diarrhoea and dehydration all of which pose a threat of death to the kitten. Between five and twelve weeks of age kittens are susceptible to infections including in particular viral pneumonia. This is caused by a lack of immunity in the kitten and before they are vaccinated.
Note: quotes are from Cat Owner’s Home Veterinary Handbook which is the source of this information.
Some posts on newborn kittens