very common dilemma for the cat breeder is 'my tom or queen
has just produced a deformed kitten. What should I do about
this? Should I breed from him or her again?'
is a question which is rarely easy to answer. Each situation
should be considered individually and many factors must be
borne in mind. Your veterinary surgeon is therefore in the
best position to advise on particular cases and you should
consult him, providing as much background information as possible.
An information sheet such as this cannot provide a set of
rules which can be applied to every case. However, it will
outline some guidelines which may be helpful to breeders planning
the most appropriate course of action to adopt if a deformed
kitten has been produced. This is an important subject which
every responsible breeder should consider very carefully for
the benefit of their own cats and the breed involved.
information sheet is concerned with congenital deformities:
these are abnormalities which are present at birth. Some of
them are very obvious and will be noticed following the most
casual observation - such as gross abdominal hernia. Others
are much less obvious and may only be discovered following
a thorough post-mortem examination - such as congenital malformations
of the organs. For this reason, it is very important that
a full post-mortem is performed on all young kittens which
die for no obvious reason. There are also many very subtle
abnormalities, such as errors of metabolism, which can only
be diagnosed by sophisticated laboratory tests on blood samples
from live kittens.
congenital abnormalities are present at birth, they may not
necessarily be apparent at this time. For example, a congenital
abnormality of the heart may not produce any signs in a young
kitten, but in time, as the kitten grows and the demands on
the heart increase, characteristic signs of heart disease
are also some hereditary abnormalities which take time to
develop. For example, retinal atrophy, although known to be
hereditary in Abyssinians, Siamese, and possibly other breeds,
is a slowly progressive disease in which no impairment of
vision or abnormality of the retinal vessels may be recognised
until the affected cats are quite old.
all congenital abnormalities are hereditary. Some certainly
do result from gene mutations, but there is another important
group of congenital deformities, the so-called non-genetic
developmental abnormalities. These are caused by disturbance
of the development of the kittens in the uterus by some non-hereditary
infections may lead to damage or death of the developing young
if they occur during pregnancy. Most of these are viral infections
since viruses tend to prefer rapidly dividing cells, and the
cells of a developing embryo or foetus are dividing particularly
rapidly, thus providing a prime target. For example, it is
widely recognised that German measles can damage the developing
baby if a mother is infected during pregnancy. There are similar
examples recognised in cats, and panleucopenia infection may
act in this way. It can selectively destroy cells in a certain
area of the brain, the cerebellum. This part of the brain
is important in controlling coordination and therefore affected
kittens are ataxic (have difficulty in balancing).
only can field virus derived from natural infections cause
this problem, but also virus used in some vaccines. Some vaccines
contain live virus which is attenuated (it does not produce
disease in kittens or adults), but it can, nevertheless, damage
developing foetuses if a pregnant queen is vaccinated. For
this reason, as a general rule, live vaccines are not used
in pregnant animals.
drugs can damage developing foetuses and these are known as
teratogens. Probably the best known example of a teratogenic
drug is thalidomide which produced deformities in the children
of mothers who had received this drug during pregnancy.
little is known about the teratogenic potential of most drugs
used in cats. Drugs must be tested for teratogenicity before
they are licensed for use in humans but their teratogenicity
may vary considerably in different species, and it is clearly
impractical to test drugs routinely for teratogenicity in
cats. We certainly know that some drugs can be teratogenic,
for example, griseofulvin, the antibiotic used for ringworm
treatment, can cause congenital deformities in developing
kittens if given to pregnant cats. But with most drugs used
for cats, we simply do not know whether or not they are teratogenic.
Therefore, as a general rule, it is best to avoid the use
of drugs in pregnant queens unless absolutely necessary.
other than drugs may also act as teratogens. For example,
it is possible that some common household substances, or food
preservatives could act in this way.
environmental factors are known to be teratogenic. Exposure
of pregnant animals to high temperatures can lead to developmental
abnormalities in their unborn young. This can occur simply
by maintaining the animals in a higher ambient temperature.
We have encountered cases where there has been a strong suspicion
of congenital deformities of kittens resulting from hyperthermia
due to exposure to high environmental temperatures.
other factors may be responsible for developmental problems
and these may be very difficult to identify. An example of
this would be inadequate development of the placenta. This
is not uncommon in humans and may lead to intra-uterine growth
retardation. A similar situation may possibly occur in cats
if the placenta fails to function correctly. It is the 'lifeline'
for the foetuses, providing all their requirements for life,
and if its function is impaired, the growth of the foetuses
will suffer. Such a problem may be particularly common in
a polytocous animal such as the cat which usually has many
young in a litter. There may consequently be competition between
the placentae for the available uterine space and some may
fail to develop fully.
question that the responsible cat breeder should ask on the
appearance of a deformed kitten is: 'Is this an hereditary
or non-genetic problem ?' Unfortunately, with many congenital
deformities in cats, we simply do not know. With some of the
more common conditions, such as cleft palate or umbilical
hernia, it is quite clear that these may be of either hereditary
or non-genetic, developmental nature.
are a number of indicators which can be used. It must be stressed
that these are not 'hard and fast' rules, and each case must
be considered individually.
If there is a strong breed disposition (ie. the condition
occurs particularly frequently in a specific breed) this suggests
some hereditary involvement, although there are other possible
causes of breed predispositions.
The presence of multiple abnormalities in the same kitten
or in different kittens in the same litter, suggests a non-genetic,
developmental problem, rather than an hereditary one. For
example, a kitten may be born with cleft palate, a twisted
spine and spina bifida - or in the same litter there may be
one kitten with a cleft palate, one with an umbilical hernia,
one with a malformed leg and one mummified. This would suggest
that it is probably a non-genetic developmental problem and
therefore not hereditary.
considering an individual case, there is much information
to examine (see table 1). In particular, if the mating has
been used before, it is useful to know the outcome. It is
also important to check whether the same deformity has been
recorded in the progeny of either of the parents, and, if
so, whether other partners in the mating were related to either
the tom or queen.
change in management, especially of diet, and any history
of illness during pregnancy may be relevant, as such factors
may be responsible for non-genetic developmental abnormalities.
In addition, difficulty during kittening may lead to damage
to the young kitten.
information to consider if a deformed kitten is produced
How many kittens were produced in the litter and how many
were abnormal ? Did they all show the same abnormality ?
Has this mating been used before and, if so, what was the
Have either of the parents been mated to other cats before
? If so, were they related (to either of the original parents),
and what was the outcome ?
Have you encountered this deformity previously, either in
your own cats or in cats of the same breed ?
Did anything unusual occur during the pregnancy ? For example,
1.) a change of diet or management ?
2.) any illness during pregnancy ?
3.) did the queen receive any drugs ?
Were there any problems with the kittening ?
the available evidence strongly suggests that the problem
is hereditary, and if the deformity is serious, the breeder
may elect to have the queen spayed. However, it should be
remembered that if the condition is hereditary, there will
be far greater ramifications to consider. Most congenital
deformities are inherited as recessive factors, in which case
both parents must be 'carriers' of the condition and also
66% of the apparently normal littermates. Furthermore, the
trait will be carried by at least 50% of the progeny of either
parent mated to other cats. It is clear, therefore, that the
implications for breeders who encounter severe deformities
of an hereditary nature are extremely serious.
in many instances, insufficient information is available to
decide whether or not a deformity is hereditary, and this
may only be determined by carrying out a series of test matings.
ideal mating for this purpose is between affected offspring
and their parents. If a recessive factor is responsible for
the abnormality, 50% of the resulting kittens will be affected.
If a simple recessive factor is suspected, it is necessary
to produce at least five normal kittens to ensure a probability
of over 95% that the condition is not hereditary, or seven
kittens to increase the probability to over 99%. Just one
affected kitten may be enough to indicate that the defect
is inherited. However, if the abnormality is so severe that
this is not practical, the original mating which produced
the affected kittens should be repeated or, failing this,
the parents should be mated with other cats known to have
produced affected offspring and therefore suspected to be
carriers. In this case only 25% of the progeny will be affected
(although a further 66% of the apparently normal progeny will
be carriers). In this case it is necessary to produce at least
11 and 17 unaffected kittens to ensure a probability of over
95% and 99% respectively that the condition is not inherited.
a mating programme may be rather an anathema to a breeder,
arranging matings in an attempt to reproduce the condition,
and breeders may be tempted to mate their cats to another
individual from a different line. Indeed, all the young produced
by this mating may well appear to be normal (unless the new
partner is also a carrier), but if the abnormality is inherited
as a recessive factor, 50% of these will also be carriers.
This may not be discovered for several generations until a
pairing is chosen between two cats with the original carrier
in both their pedigrees. The trait may then be well disseminated
throughout the breed and difficult to eradicate. The responsible
breeder will therefore act immediately if deformed kittens
it becomes apparent that a congenital abnormality is particularly
common in a certain breed. This does not necessarily indicate
that the abnormality is inherited, and it is possible that
certain breeds may tend to express non-genetic developmental
disturbances in a particular way. The importance of some hereditary
conditions may be affected by the breed. An example of this
would be hip dysplasia in the dog, a condition involving a
deformity of the hip joints. In small breeds, the condition
may have very little effect on the gait, but in large, and
consequently heavier breeds, this can be a crippling deformity.
Breed variation in the expression of congenital deformities
is generally less significant in cats since there is not such
a range in size and conformation between breeds.
congenital deformities usually of a polygenic (ie. controlled
by a number of genes rather than a single gene) may be associated
with breed conformation. For example, lacrimal (tear) overflow
may be seen in very 'typey' long-hair cats since a particularly
short nose may lead to deformity of the naso-lacrimal ducts
(which drain tears from the eye to the nose).
is important that if a breed predisposition is suspected,
investigations should be undertaken to determine whether the
condition is inherited and, if so, its mode of inheritance.
This information may be required if the trait is to be eliminated.
first step is to determine the prevalence of the condition
and to collect as much information as possible about individual
cases (see table 2). In the case of some deformities, a thorough
clinical investigation, possibly supported by laboratory tests
or pathological studies, may be required to confirm the diagnosis
and to differentiate from other conditions which cause similar
clinical signs. Collation of pedigrees of affected individuals
may also provide evidence of common ancestry and possibly
an indication of the mode of inheritance. Unfortunately, the
stigma that many breeders feel is associated with congenital
deformities may discourage open discussion of such problems
and free exchange of information. In this situation the breed
club may elect to request the assistance of an impartial collator.
Breeders may be more willing to provide information about
cases to such an individual if they are assured of confidentiality.
For this reason, and because of the availability of veterinary
expertise, which may be required both to provide a definitive
diagnosis and to investigate further the nature of the deformity,
breed clubs may request the help of the Feline Advisory Bureau.
of deformities with suspected breed disposition
Circulate a questionnaire to:
1.) Determine the extent of the deformity
2.) Obtain information about the nature of the problem
3.) Collect information on the breeding and pedigrees
of affected kittens
Collate the breeding results and pedigrees
Organise a test mating programme
next step is to determine the precise mode of inheritance
of the deformity. This will usually necessitate a test mating
programme, but in some cases sufficient data may be available
from random matings if detailed records and pedigrees are
available. Considerable care, however, is required in collating
the pedigrees of kittens from less common breeds. There may
be a limited number of stud toms available for such breeds
and the same studs will inevitably appear frequently in pedigrees,
particularly if they have been very popular. Hereditary deformities
are likely to appear more frequently in small breeds for this
very reason, especially if it is a new breed which has increased
in popularity rapidly and has been derived from a relatively
small genetic pool. The genes responsible for congenital deformities
may not be more common in such breeds but the chance of affected
kittens may be higher due to a necessarily higher degree of
success of an investigation of this type is dependent mainly
on the participation of breeders. Unless breeders provide
detailed information about cases, there will be insufficient
data for meaningful analysis. It is also important for breeders
to appreciate that investigations of this nature may take
considerable time to complete. A test mating programme is
a major undertaking and requires extensive resources, although
it may be possible for a number of breeders to arrange a series
of matings under the direction of a collator. However, a conflict
may arise for the collator between the requirement to maintain
confidentiality concerning information passed on by breeders
and the need, inevitably, to disclose some information in
suggesting suitable pairings for the test mating programme.
Even if an extensive test mating programme of this type is
performed, it may prove difficult to define the precise mode
of inheritance for a number of reasons:-
The deformity may be polygenic rather than due to a single
gene mutation. Its inheritance may therefore be highly complex.
It may be a deformity that can be either hereditary or of
a non-genetic developmental nature.
The severity of the deformity may vary. This may be due to:
A single gene with variable expressivity or incomplete penetrance
Although the deformity may depend primarily on a single
gene mutation, other factors, such as diet, may contribute
to its severity in individual cases.
Threshold factors may be involved.
the hereditary nature of a defect has been confirmed and its
mode of inheritance has been determined, the breed club can
decide on an appropriate course of action. If the defect is
mild, and is of purely aesthetic importance with no deleterious
effect on the cat's health, it may not be considered necessary
to take any action. If it is a serious defect, the course
of action may depend on the prevalence of the defect. A rare
deformity which is restricted to just one or two lines of
cats may be eliminated relatively easily. However, if the
deformity is widespread, it may prove impossible to eliminate.
For example, if the incidence of a deformity is 1:100 cats,
there may be 18 carriers in every 100 individuals.
is therefore vital that every responsible cat breeder and
breed club should make every effort to identify hereditary
deformities as soon as possible to avoid perpetuation of the
trait. Hereditary deformities do not disappear if ignored
- they get worse. There is also considerable merit in the
policy of collating information on all congenital deformities
either through the breed club and the GCCF, or through the
FAB register of such anomalies.
to send a dead kitten for investigation
This applies to the UK only!)
you intend sending a kitten for investigation at The Feline
Centre, Langford, please observe the following:
You must consult your veterinary surgeon and obtain his agreement
before you send the kitten.
Include as many of the details described in this information
sheet as possible.
Send the kitten by first class post, wrapped in absorbent
material (preferably cellulose wadding paper, but alternatively
in tissue or cotton wool) and packed in a 'Jiffy' bag or an
uncrushable package. DO NOT use a plastic bag, this is particularly
important in summer as high temperatures will lead to 'sweating'
and rapid deterioration.
If a kitten dies at the end of the week, or at the weekend,
and a delay of more than two days is likely between despatch
and receipt at Langford, the kitten should be stored temporarily.
This can be done by placing the kitten in a fridge or deep
freezer. Tissues will continue to deteriorate in a fridge
(but not so rapidly) and subsequent histological interpretation
may not be possible. If histology is likely to be important
in a particular case, this problem can be overcome by fixing
(pickling) small portions of the desired tissues in 10% formal
will not usually interfere with virus studies and will minimise
deterioration of the tissues but does interfere with bacteriology
(by selectively killing some bacteria), and histology (the
ice crystals that form disrupt the tissues). It does have
the advantage of enabling indefinite storage. Ideally, a kitten
stored frozen should be received at Langford without thawing