by Professor Tim Gruffydd-Jones, University of Bristol

Presented at the FAB conference, October 2002

THE TERM ‘FADING KITTEN' IS OFTEN interpreted as linked to a specific form of death in young kittens. However it is purely a descriptive term giving no indication of the underlying cause and can be very misleading. A much more appropriate term is neonatal mortality. This covers death around the time of birth (peri-natal mortality) and death during the first few weeks of life when the kittens are still highly dependent on their mother.

Neonatal mortality rates can be quite high – up to 10 per cent or more, and constitute the bulk of cases of deaths prior to weaning.

Neonates are relatively tolerant of hypoxia (low oxygen) In addition their haemoglobin type maximises the efficiency of oxygen transfer. It is therefore worthwhile persisting for some time in efforts to revive any kittens which appear reluctant to breathe.

Kittens have little thermoregulatory control over the first few weeks of life and depend on the warmth provided by their mother's body and a dry, warm nesting environment. Chilling will soon lead to depression of the suckling reflex with consequent hypoglycaemia (low blood glucose) and death. Most queens have very strong maternal instincts and make good, attentive mothers. If a cosy nest box is provided the queen's body heat will ensure that the immediate nesting environment temperature is adequate. Again, it is important that the queen is settled in the nest box. If not she may constantly be moving the kittens, which can lead to chilling. Nest boxes should be made of material that can be suitably disinfected or discarded after use.

Regular suckling, particularly immediately after parturition, is vital. Neonates are vulnerable to hypoglycaemia and regular feeding is necessary to ensure this does not occur. Hypoglycaemia leads to suppression of the suckling reflex which accentuates the hypoglycaemia and will rapidly end in death.

Suckling in the first few days of life is also important to ensure that good levels of maternally derived immunity (MDI) are achieved. Negligible levels of antibodies are usually obtained by placental transfer prior to parturition and kittens depend on colostrum for MDI although colostral transfer may continue for up to 72 hours, most occurs within the first 24 hours and it is therefore vital that the kittens suckle well during this period. Regular use of vaccine boosters for the queen, preferably just prior to mating, will also assist in ensuring that

good levels of MIDI are achieved.

Contented kittens spend around 90 per cent of their time sleeping for the first few weeks of life. they are born blind and their eyes begin to open seven to 10 days after birth. From around three weeks of age they become more adventurous, emerge from the nest box and begin to feed themselves, often sharing some of the queen's solid food before they learn to lap fluids.

Recognising problems in young kittens

The critical nature of the neonatal period has been emphasised above and certain losses are inevitable over this period, even with optimum neonatal management It is important, therefore, in investigating kitten mortality in a cattery to establish the extent and pattern of losses and to assess whether these losses are acceptable. Extensive databases on kitten mortality exist for cat colonies, but much less information is available for breeding catteries. An acceptable maximum figure for mortality rates up to weaning is probably around 10 per cent, half of this representing stillbirths. Average birthweights of mixed breed, colony-maintained cats are around 100g. However, much lower normal birthweights should be expected in some pedigree kittens, particularly of the lighter framed Oriental breeds, which tend to have much larger litters.

Regular weighing of the kittens can provide a useful assessment of performance and had the added advantage of accustoming the kittens to handling from a young age. Colonymaintained cross-bred kittens will gain up to 30g daily, but weight gains may be much more modest for pedigree kittens, particularly for kittens from large litters.

There are limited ways in which young kittens demonstrate distress, irrespective of the underlying cause. They may be much more restless than normal, fail to sleep contentedly for prolonged periods as should normally occur and may cry excessively. They tend to wander aimlessly predisposing themselves to chilling. The queen may appear to neglect sick kittens and they maybe found away from the next box. They cease feeding and the suckling reflex becomes depressed. In view of the limited range of clinical signs sick kittens display, clinical examination is generally unrewarding. In many cases a diagnosis can be made only at post-mortem examination and this will often reveal infections and congenital abnormalities which would otherwise pass unnoticed. This may ennoble preventative action to protect the remainder of the litter or may provide useful information on which to base future breeding plans.

The major causes of death in young kittens are environmental and managemental factors, maternal factors, infections and congenital conditions.

Environmental and management factors

Post mortem examination fails to reveal a clear cause of death in a large proportion of kittens which die within the first few days of life. Undoubtedly environmental and management factors, particularly chilling and failure to suckle, considered above, are responsible for many of these. The loss of occasional kittens may simply reflect inattentive queens, but major losses in the first few days of life suggest some basic mismanagement problem. This can be investigated satisfactorily only by visiting the cattery, by detailed study of the normal husbandry measures and by assessment of breeding records.

Maternal factors

Management of the queen is crucial in the general management over the neonatal period. Maternal factors may also play an important role in infectious problems either through contributing to protection or predisposing to infection.

The queen is the major source of early protection against infectious agents in the form of MDI derived from colostrum. However, the queen may also predispose to infectious disease by acting as a source of infection as a consequence of her carrier status or development of mastitis. She may also play a role in umbilical infections.

Bacterial infections

An important route of infection in new-born kittens is the umbilicus. The kitten may be infected by vaginal organisms during birth or by opportunist organisms in the environment after birth. Infection may track up the umbilical vessels to cause a liver abscess or it may lead to peritonitis. Several kittens in the litter, or frequently the complete litter, may be affected. Close examination of the umbilicus will sometimes reveal slight discoloration or swelling. Antibiotics are indicated for treatment, but the response in established cases is poor.

Another quite common source of infection in pre-weaning kittens is infected milk from mastitis in the queen. In acute mastitis the queen will show clinical signs, but in chronic mastitis the queen may seem well and her mammary glands may appear normal. Mastitis leads to gastroenteritis in the kittens with diarrhoea and occasionally vomiting. The kittens must be separated from their mother and hand-reared.

Viral and chlamydial infections

Viruses can be a major cause of disease in young kittens in breeding catteries but not usually until a little later. Kittens are most vulnerable between four to six weeks of age when maternally derived immunity is waning. The respiratory viruses and chlamydia are generally the most important infections in kittens.

Miscellaneous disorders

Young kittens are very vulnerable to trauma and this is an important cause of death. External injuries may not be obvious, but recent trauma may become evident on post-mortem examination.

Neonatal isoerythrolysis

This condition involves an incompatibility in the blood group of the kittens and their mother It can occur if a group B queen has group A kittens. Some such queens have potent antibodies against group B blood. These antibodies are present in the colostrum and will be absorbed for up to the first 24 hours after birth. They destroy the red blood cells leading to anaemia. Affected kittens may die in the first two to three days. This problem is more frequent in certain breeds which have a high prevalence of group B individuals – such as British Shorthairs, Birmans and Devon Rex.

Congenital abnormalities

There are many congenital abnormalities of cats which may become apparent during the first few months of life and some of these may cause death of young kittens. Some will be discovered on casual examination of the kittens, but in other cases a post mortem examination will be required to reveal their presence. Many inborn errors of metabolism are recognised in man and other species and these can only be diagnosed in life, often requiring sophisticated laboratory investigation. A few such congenital defects of metabolism have been recognised in cats, but they have received little consideration in this species and it is likely that they may account for some of the occasional losses encountered in young kittens.