Kitten deaths are a cause of distress for both breeders and owners, but the causes and prevention of deaths are similar whether the situation is the breeding, home or rescue/shelter environment.
When breeding cats, it is inevitable that some kittens will die, and a low level of loss has to be expected. Generally pedigree cats have higher levels of kitten death than non-pedigrees. In one large study of pedigree cats, around 7% of kittens were still-born (dead at birth), and a further 9% died during the first eight weeks of life (most in the first 1-3 weeks). The proportion of kittens alive at 8 weeks of age varied between breeds (from around 75% to 95%) with the highest mortality among Persian kittens.
Death before weaning
The majority of kitten deaths occur before birth (still born kittens) and during the first week of life. Once past the first week, mortality rates decline dramatically. Most early deaths result from non-infectious causes, while the mortality rate can rise a little again after weaning as infectious diseases become more common. Most kittens receive protection against many infectious diseases during the early weeks of life from the queen (maternal-derived immunity). Kittens dying between birth and weaning are frequently called ‘fading kittens’.
Neonatal (newborn) kittens may die suddenly, or ‘fade’ within a few days. Unfortunately, the clinical signs of many of the diseases affecting newborn kittens are very similar and vague. While normal kittens tend to cuddle together and sleep contentedly between feeds, sick kittens tend to lie separately, are generally more restless, are not keen to suck, and cry frequently (if still strong enough to do so).
Newborn kittens are vulnerable because mechanisms which regulate temperature control are poorly developed, they are at increased risk of dehydration and low blood sugar (hypoglycaemia), and the immune system is immature. Therefore, regardless of the initiating cause, these kittens can rapidly die.
Major causes of death before weaning
Hypothermia – Newborn kittens are predisposed to hypothermia because they cannot regulate their temperature and rely on the queen (and the environment) for warmth. Hypothermia is particularly harmful as it can result in decreased heart and respiratory rates which can lead to cardiovascular failure. Also, with hypothermia kittens often fail to suck milk effectively , which exacerbates the problem. The rectal temperature of kittens should be 35–37C in the first week, 36–38C in the second and third weeks, and reaches normal adult levels of 38–39C by the fourth week.
Low blood sugar (hypoglycaemia) – Newborn kittens have high energy requirements but no energy reserves so are highly dependent on the milk from the queen. Any kitten that is ill, stressed or has inadequate milk intake may rapidly develop hypoglycaemia. This may be seen as weakness, hypothermia, crying, difficult breathing, and ultimately seizures, coma and death.
Dehydration – Young kittens have a high risk of dehydration because their bodies have a higher water content and they are much less able to regulate water loss compared with adults, losing water readily through their kidneys, lungs and skin. Any diarrhoea will also increase water loss. The normal fluid requirements of a neonatal kitten are around 130-220 ml/kg/24h compared with just 50-65 ml/kg/24h for an adult. Dehydration will readily occur with inadequate milk intake or excessive fluid losses (usually as a result of overheating or diarrhoea).
Common causes of ‘fading kittens’
Birth and queen-related factors
- Hypoxia (lack of oxygen), trauma, hypothermia – kittens born after difficult birthing (dystocia) have a higher risk of death and this may be the most significant cause of early deaths. This results from lack of oxygen (hypoxia) and/or trauma. Studies have shown that cats with extremes of body conformation such as the ‘flat-faced’ Persians experience more birth difficulties, probably as a combined result of the kittens being relatively large (with large heads) and the pelvis of these cats being narrow. Lack of oxygen during birth can result in stillbirth, or the birth of weak kittens that fail to suck.
- Kitten mortality also tends to be higher in the first litter born to a queen, which probably relates to inexperience, trauma and possibly cannibalism. Older queens (after their fifth litter) may also experience more problems.
- Kitten mortality also increases with increasing maternal obesity, and with other queen-related causes such as a lack of milk, mastitis, or maternal neglect.
A congenital abnormality is a physical defect present from birth. Such defects may be genetic (inherited) or simply developmental (for example exposure to teratogens – drugs, disease or other conditions – which induce defects in the developing foetus). Common congenital defects include:
- Cleft palate
- Umbilical hernia
- Skeletal defects
Severe defects usually result in stillbirth or early neonatal death. Milder disorders may result in fading kittens, or only become apparent later in life. Because inbreeding increases the risk of genetic disease, congenital disorders are seen more frequently in pedigree cats.
Low birth weight
Underweight kittens are particularly susceptible to hypothermia, dehydration, respiratory failure and infections, and have a significantly increased risk of neonatal death. Kittens may be born underweight because of maternal malnutrition or ill-health, congenital disease, infections, or any condition that results in poor placental blood supply.
The average birth weight for most breeds of cat and moggies is around 90-100g, but it is normal for some breeds to have smaller kittens (e.g., Orientals) and some to have larger kittens (e.g., Maine Coon). In general, newborn kittens weighing less than 75g are likely to have an increased risk of death.
Inappropriate environment (temperature, humidity, hygiene, overcrowding, over-handling)
Environmental factors can be important causes of fading kittens. These include:
- Extremes of temperature – providing kittens with a suitable environmental temperature is essential and a kitten that has ceased to suck will quickly become cold and hypoglycaemic. Supplemental heating may be needed (and will always be needed if kittens are hand-reared) to maintain an environmental temperature of 29–32C in the kitten box, although they should have the freedom to move away to cooler areas if needed. The temperature can be gradually reduced to around 27C by 7-10 days and can go down to 22-25C by the end of the first month.
- Poor hygiene – will increase the risks of infectious diseases
- Overcrowding – will lead to increased risks of infectious diseases and malnutrition resulting from competition for milk/food
- Over-handling – this may limit the kitten’s feeding time, and with nervous queens may result in cannibalism of her kittens. Since newborn kittens cannot shiver and are unable to control their own body temperature, hypothermia will result, and this will lead to a further reduction in activity and sucking.
It is vitally important to feed the queen an appropriate diet – the nutritional demands of a queen producing milk for her kittens are extremely high and incorrect nutrition can affect the quality of the milk she produces. It is important that the queen is fed a high quality commercial cat food designed to meet the demanding nutritional needs of lactation.
Inadequate milk production may be associated with:
- An inexperienced or nervous queen
- Old queens
- Sick or malnourished queens
- Mastitis (infection of the mammary glands)
- Systemic illness
- It may sometimes be a familial trait
Inadequate milk intake by the kitten can also result from:
- Anything causing ill-heath or weakness
- Competition or bullying from other kittens
- Environmental factors or over-handling that interferes with the queen-kitten bond
Monitor food intake and growth of kittens:
- Weigh kittens at birth, daily for the first week, then at least twice weekly until weaned
- Up to 10% weight may be lost in the first 24 hours
- After this, daily weight gain should be around 10–15g/day (5–10%)
- Kittens should double their birth weight by 1-2 weeks of age
- Any weight loss (or lack of weight gain) should be investigated
If milk supply or intake is inadequate, supplemental feeding will be needed.
Neonatal isoerythrolysis (NI)
In certain cat breeds neonatal isoerythrolysis (NI) is a relatively common cause of fading kittens, caused by incompatibility between the blood type of the queen and the kitten. For more information see [Blood groups and incompatibility].
Infections (viral, bacterial, parasitic)
Normal kittens should suck for the first time within 2 hours of birth – they can absorb antibodies from the queen's milk during the first 16–24 hours of life and it is vital they suck well during this period both for good nutrition and also to receive this critical maternal-derived immunity (MDI, or maternal-derived antibodies – MDA) to protect them from infections. The effect of MDA will usually begin to fade when the kittens are three to four weeks of age but varies between individuals and will depend on the amount of antibodies present and the amount absorbed. The kittens’ natural immunity is still developing as MDA wanes, and since most vaccine regimens do not start until around eight weeks of age, this can leave a period of time when the kittens are particularly at risk for infectious diseases. Kittens that do not suckle will receive insufficient colostrum and so will not be protected by MDA and are particularly susceptible to infectious diseases at an early stage.
Factors that may contribute to an increased risk of infectious diseases in kittens include:
- Inadequate colostrum intake
- Inadequate nutrition
- Low birth weight
- Lack of oxygen at birth
- Congenital disorders (especially of the immune system)
- Overcrowded environment
- Poor hygiene
- Low environmental temperature
Respiratory and gastrointestinal infections are seen most frequently, and important infectious agents associated with fading kittens include:
- Respiratory tract
- Gastrointestinal tract
- Feline coronavirus (FCoV)
- Feline parvovirus (FPV)
- Salmonella species
- Campylobacter species
- Giardia lamblia
- Isospora species
- Systemic diseases
In kittens, bacterial infections are often seen secondary to viral infections (cat flu, FeLV, FIV, FPV, FIP), although they can be seen as primary infections also. Clinical signs depend on the site, nature, and severity of the infection but may include diarrhoea, coughing, breathing difficulties, arthritis, or dermatitis, as well as the less specific signs more typical of fading kittens. Ultimately, many of these infections result in septicaemia (where the blood stream is invaded by large numbers of bacteria) and death.
Intestinal parasites (including roundworms and coccidia) can be a problem where queens are not wormed, or where hygiene is inadequate. Heavy infestations of kittens may result in a poor body condition, soft or bloody faeces, inappetence, a pot-bellied appearance, weight loss, and occasionally death.
General approach investigating kitten mortality
Determining the cause of fading kittens can be very difficult, and many cases are multifactorial. Clinical signs are also generally non-specific and the small size of kittens makes collection of samples difficult. Generally, concern should be raised when pre-weaning kitten losses exceed 20%, post-weaning losses exceed 10%, the number of losses suddenly increases, or a particular cause of death is seen more frequently. Careful records of all animals (including all kittens) should always be kept in a breeding cattery, and all diseases and deaths should be noted.
Investigation usually involves looking at the entire cattery. In many cases it is possible to improve some aspect of the environment, management, and/or nutrition of the kittens. A full investigation will include looking at:
- The background and history of the cattery
- Evaluation of the environment (often including visiting the cattery)
- Evaluation of cattery management, including hygiene, disinfection, stocking density, feeding, vaccination, worming etc.
- Examination of both sick and healthy kittens
- Potentially collection of blood samples or swabs from kittens, and/or a post-mortem examination of any dead kitten(s) … the latter can be particularly helpful
- Examination of breeding queens, particularly the mothers of any fading kittens