surgeons in practice spend most of their time in preventing
rather than promoting breeding in cats. However, cats, and
particularly pedigree cats, are becoming more popular as pets,
so the demands on the veterinary profession for advice on
breeding and its problems are likely to increase.
is a subject which has received scant attention in the veterinary
literature in the past, in fact their has been little information
available about normal reproduction. For example, until recently,
normal hormonal patterns throughout oestrus and pregnancy
in the cat were not known. Over the past few years, however,
a number of studies into feline reproduction have begun.
failure can arise at a number of different stages throughout
the reproductive process. Firstly, a queen may fail to ever
call or display oestrus. Even if she does call, she may refuse
to mate - mating failure. Failure of ovulation, fertilisation
and pregnancy may all occur, and finally there may be difficulty
at the time of kittening. In addition, problems may occur
in either queens or toms.
the limited space available it is not possible to cover all
aspects of this wide subject. Instead, we intend to concentrate
on failure of ovulation, fertilisation and pregnancy. In other
words, any problem that arises in queens from the time of
a successful mating to parturition. These seem to be the stages
at which most difficulties are encountered and are the problems
veterinary surgeons in practice are most frequently called
upon to diagnose.
physiology of pregnancy
of the most interesting features of the reproductive process
of cats is the phenomenon of induced ovulation. This has a
number of important consequences:
All sterile matings necessarily lead to pseudo-pregnancy
Vaginal cytology may not be suitable for investigation of
reproductive function in cats
Progesterone assays can be used to confirm ovulation
eggs are fertilised in the oviduct and arrive in the uterus
4-5 days after mating. For the first 10 days the blastocysts
are nourished by the uterine milk secreted by the endometrial
glands. The process of implantation begins 14 days after mating.
By 20 days the conceptual swellings are approximately 'pea-size'
and it is at this stage that pregnancy can first be confirmed
by abdominal palpation. However, the optimum time at which
to carry out pregnancy diagnosis by abdominal palpation is
4-6 weeks when the conceptual swellings vary from 'walnut-size'
to 'bantam-egg-size'. 3-4 weeks following mating most queens,
particularly maidens, show marked reddening of the teats.
This phenomenon is referred to as 'pinking-up' by breeders
and is used as an indication of pregnancy. However, this will
also be seen in pseudopregnant queens and cannot be relied
upon to confirm pregnancy. Indeed, as already explained, pseudopregnancy
involves formation of corpora lutea and production of progesterone
in just the same way as pregnancy.
actions of progesterone may cause pseudopregnancy to mimic
the changes of pregnancy. For example, it leads to fat deposition
and changes in water balance and will cause considerable abdominal
enlargement. Therefore, confirmation of pregnancy by abdominal
palpation is required to differentiate between pseudopregnancy
and pregnancy. Pseudopregnancy in the cat rarely involves
pseudo-lactation as is so commonly seen in the bitch. The
lifespan of pseudopregnant corpora lutea is very variable
and pseudopregnancy may last from 3-7 weeks. Therefore, in
some cases a pseudopregnant queen may return to call at the
same expected date as if unmated, whilst in other cases there
may be an extended period of inactivity before onset of the
6 weeks the conceptual swellings begin to merge and cannot
be identified individually again until the last two weeks
of pregnancy, particularly if the queen is carrying a large
litter. However, by this time the abdominal distension will
usually be obvious.
of the foetal skeletons cannot be recognised radiographically
until the last week or so of pregnancy.
corpora lutea are essential for the maintenance of pregnancy
during the early stages. There is some disagreement concerning
the stage of pregnancy after which ovariectomy, and hence
removal of luteal progesterone, will not induce abortion.
It is presumed that after this stage the placentae and/or
foetuses produce sufficient progesterone to maintain pregnancy.
A rapid increase in progesterone occurs soon after mating,
followed by a gradual decline which becomes precipitous during
the last week of pregnancy until the levels have returned
to basal values at the time of parturition. The high oestrogen
values of oestrus soon fall away after mating. There is a
peak in oestrogens during the sixth to eighth weeks of pregnancy,
the magnitude of which may be related to litter size, followed
by a rapid fall during the last week.
of gestational failure
failure can occur at various stages of pregnancy and may take
Early Embryonic Death
involves death of the blastocysts between the time of fertilisation
and implantation. A certain level of EED can be considered
normal and is considered to represent foetal wastage resulting
from natural selection. Because of its phenomenon of induced
ovulation, the cat is ideally suited to a study of EED. It
does seem that "normal" EED rate is low in cats.
Resorption and Abortion
by the uterus of the conceptual tissues may occur after either
foetal or placental death. Once calcification of the foetal
skeletons is well established resorption is not possible.
The distinction between resorption and abortion is not always
clear cut. Passage of partially resorbed "liver-like"
tissue by queens during pregnancy is a common occurrence.
On some occasions the tissue may consist purely of resorbed
placenta, whilst on others, a partially resorbed foetus may
be attached. It is common for resorbed placentae and foetuses
to be passed at parturition together with live kittens in
cases of large litters, particularly from Oriental queens.
These deaths possibly result from "over-crowding"
and are not considered to represent reproductive failure.
of forms of gestational failure
of abortion is self-evident. Resorption occurs after implantation
and can therefore be identified by failure to produce kittens
after pregnancy has been confirmed by abdominal palpation.
EED must be differentiated from both fertilisation and ovulation
of the inter-oestrual period cannot be relied upon to identify
the latter due to the variability in the duration of the pseudopregnancy
mentioned previously. It is necessary either to examine the
ovaries at laparotomy or measure plasma progesterone, as described
earlier, after mating to determine whether or not ovulation
and investigation of EED
of EED requires specialised techniques and is not feasible
in general veterinary practice. I shall therefore only briefly
laparotomy is performed four to ten days after mating and
collection of the eggs from the oviducts or uterus is attempted.
Microscopic examination enables determination of fertilisation
status, morphological abnormalities, or degeneration possibly
indicative of an unfavourable uterine environment. If healthy
eggs are present these are cultured and subsequently evaluated
cytogenetically. It is unlikely, however, that chromosomal
abnormalities will account for complete reproductive failure.
It is much more likely merely to cause a reduction in litter
size. At laparotomy it is also possible to evaluate the ovaries
for adhesions and the oviducts for any blockage which might
impede the passage of eggs.
and investigation of resorption/abortion
is more common than abortion, and indeed seems to be the most
common manifestation of reproductive failure in pedigree queens.
The causes can be divided into three main groups.
environmental and managemental factors influence reproduction
in the cat. For example there is, in many groups of cats,
a definite breeding season.
length seems to influence seasonality more than temperature,
and constant lighting of 14 hours per day will abolish anoestrus
periods. Social stimuli also appear to be important. However,
it is not known whether phenomena such as the Bruce effect
can operate in the cat to induce resorption. (The Bruce effect
involves the resorption of foetuses when a pregnant female
mouse is exposed to the pheromones of any male mouse other
than the sire of the litter).
importance of nutritional problems as a cause of reproductive
failure in pedigree cats is overemphasised. Deficiencies of
Vitamin A, Calcium and Iodine have been shown experimentally
to impair reproduction but only when grossly imbalanced diets
have been fed. Most pedigree queens receive sensible diets
and such marked deficiencies are unlikely to occur in practice.
imbalances, too, have probably been overplayed in the past
as a cause of resorption and abortion and many undiagnosed
cases have been mistakenly ascribed to such problems. Ignorance
of the normal hormonal patterns in cats, until only recently,
has prevented substantiation of endocrinological imbalances.
Cysts are a potential source of abnormal levels of hormones
and are common in the cat. Parovarian cysts are often encountered
at routine spaying of immature queens. They appear as thin
walled, fluid filled structures, of variable size, often quite
large, attached to the oviduct, uterus or broad ligament.
They do not appear to be of any clinical significance.
ovarian cysts are usually encountered as incidental findings
on examination of tracts from queens with satisfactory breeding
performance records. They do not, therefore, seem to be a
significant cause of reproductive failure in cats.
deficiency has also been suggested as a cause of habitual
resorption/abortion in cats. Such queens will supposedly carry
their litters to term if injected with progesterone during
pregnancy. However, progesterone has, as in other species,
a relatively short half life in the cat and a single injection
is likely to be of little value.
number of queens with histories of habitual resorption purportedly
resulting from this problem have been studied at Langford.
However, only in one case has there been any evidence to substantiate
a diagnosis of progesterone deficiency, and from all others
FeLV has been isolated. It has been suggested that this condition
is analogous to luteal phase inadequacy in man and results
from premature regression of the corpora lutea before the
foeto-placental unit can produce sufficient progesterone to
maintain pregnancy. The progesterone levels from these cases
attained normal peak values and have then followed the pattern
for pseudopregnancy. The conceptual swellings appear to decrease
in size at the same time as the progesterone levels begin
to fall, but laparotomy at this time has indicated that the
foetuses die at an earlier stage and that the size of the
conceptual swellings does not provide an accurate assessment
of foetal well being. In the only case of probable luteal
deficiency, the peak values of progesterone were much lower
than normal. A progesterone implant inserted early in pregnancy
enabled the pregnancy to proceed normally.
progesterone deficiency is of any practical significance it
is more likely to result from foeto-placental insufficiency.
Single foetuses may not produce enough progesterone to maintain
pregnancy and are therefore resorbed. This might explain why
the occurrence of litters of a single kitten is unusual. Non-hormonal
placental insufficiency may also contribute to reproductive
failure. At the present time a lack of suitable tests for
monitoring foeto-placental function prevents verification
of this possibility.
as viruses are the most significant cause of the major infectious
feline diseases, so they are important in causing reproductive
Feline Leukaemia Virus An association between FeLV
and reproductive failure has been suspected for some time.
It now seems that FeLV is probably the most important cause
of resorption in the pedigree cat, particularly in the cattery
where more than one queen is affected at the same time. Indeed
reproductive failure is usually the first indication of FeLV
infection in entire queens who subsequently develop lymphosarcoma
or some other FeLV related disease. The exact manner in which
FeLV causes reproductive failure is not known. Possibilities
death as a direct result of infection.
of endometritis due to immunosuppression leading to an
unfavourable uterine environment.
or prenatal infection has been demonstrated but it is not
known whether this results from genetic, epigenetic or transplacental
view of the strong association between FeLV and reproductive
failure, all infertile cats should be screened for the virus.
Feline Infectious Enteritis The affinity of the
panleucopaenia virus for rapidly dividing cells and the subsequent
cerebellar damage to kittens born of queens infected during
pregnancy are well recognised. It seems likely that this virus
could cause foetal death at other stages of pregnancy. However,
FIE is probably not a significant problem in practice due
to the efficiency and widespread use of vaccines.
Respiratory Virus FVR infection by abnormal routes
of entry has been shown experimentally to cause placentitis
and abortion. Certainly pregnant cats with acute respiratory
virus infection may subsequently resorb or abort their foetuses
although it is not certain whether this is the result of placentitis
or non-specific pyrexia and illness. There is no convincing
evidence to suggest that sub-clinical infection in carrier
animals is a significant cause of reproductive failure.
Feline Infectious Peritonitis Until recently FIP
infection could only be recognised by the presence of associated
clinical signs. Since the prognosis, once signs have developed,
is hopeless and it is primarily a disease of young cats, little
opportunity has been afforded for any associated reproductive
problems to become evident. However, now that the recently
developed serological tests have indicated that FIP infection
is more common than was originally thought and epigenetic
transmission has been demonstrated, it is likely that efforts
will be concentrated on clarifying the apparent association
with reproductive failure. There is some evidence of such
a link but this could result from the association between
FIP and FeLV rather than any action of FIP itself.
specific bacterial infectious causes of reproductive failure
nor venereally transmitted infections are recognised in cats.
This species seems naturally immune to brucellosis and leptospirosis.
However, a number of bacteria - particularly staphylococci,
streptococci and coliforms - may be associated with reproductive
failure. The findings of Dr. Povey and myself indicate that
the assessment of the significance of any bacteria isolated
from infertile cats is difficult for a number of reasons:-
vaginal flora of the cat is not representative of the
picture in the uterus - which is usually sterile.
bacterial flora varies at different stages throughout
the reproductive cycle. It is therefore vital to take
serial swabs and not to rely on the results of a single
sample. At oestrus the cervix is open and therefore swabs
do provide a more representative picture of the uterine
flora. However, the high levels of oestrogens at oestrus
facilitate control of infections and the results of swabs
taken at this time may be misleading.
streptococci, coliforms, etc. are isolated with the same
frequency from both infertile and "normal" queens.
if bacteria are isolated they may only be secondary to
some other problem, such as FeLV or chronic endometritis.
is a common cause of reproductive failure in the cat, probably
secondary only to FeLV in importance. Various grades of severity
are seen. In mild cases the placentae may function efficiently
until approaching the terminal stages of pregnancy and the
condition may be manifested by the birth of stillborn kittens.
In other cases, the uterus may initially support the growth
of foetuses, but these subsequently die and are resorbed.
If changes are severe the blastocysts will not survive the
hostile environment and eventually frank pyometra may develop.
endometritis probably results from a number of factors - primarily
hormonal creation of a uterine environment suitable for the
development of secondary bacterial infection. Vaginal swabs
may not be useful in diagnosing this condition for reasons
discussed earlier and the only satisfactory method of confirming
chronic endometritis, particularly in mild cases, may be by
direct examination of the uterus, possibly with endometrial
biopsy, at laparotomy.
with severe endometritis will not breed again, but in mild
cases there may be a return to normal fertility. Antibiotics
seem of little help, the most valuable approach is to leave
the queen unmated for at least two calls in the hope that
she will be able to clear herself of infection naturally.
progesterone dominated uterus is particularly susceptible
to infection and progestagens may exacerbate endometritis.
Therefore, in view of the frequency of this condition, empirical
use of progestational agents in cases of reproductive failure
of uncertain aetiology is positively contra-indicated.
the cat is the primary host of Toxoplasma gondii ,
experimental studies have failed to demonstrate either reproductive
failure or congenital infection associated with infection.
This organism is therefore thought to be of little practical
importance as a cause of reproductive failure in cats.
conclusion, reproductive failure and reproduction in the cat
have only received serious attention during the past few years.
Our knowledge of even the normal reproductive process of the
cat is scant at present and many questions about reproductive
failure are unanswered.
recently, very little attention has been paid to the problems
of fertility in the tom cat. The impression gained from reading
the textbooks is that male fertility is almost inevitably
above suspicion and that it is the poor female who fails in
her duty. However, we are now beginning to realise that the
tom does have his problems too and that these require some
affecting fertility in male animals can be divided arbitrarily
the first group, anatomical factors can again be sub-divided
into developmental and acquired abnormalities.
Cryptorchidism : This is a failure of the
testes to descend from the abdomen into the scrotum. During
foetal life the testes lie within the abdomen, close to the
kidneys. Normally, as the animal develops, the testes migrate
posteriorly through the inguinal ring and finally come to
lie outside the body. The testes are normally descended at
birth but may not be palpable until the animal is four to
twelve weeks old. If they have not descended by six months
of age, they probably will not do so. When the condition is
bilateral the animal is sterile because the deep body temperature
is too high to allow normal spermatogenesis. If the condition
is unilateral, one testis is normally descended. (The animal
is not a mon-orchid since this implies that he has one gonad.
He has two, but only one is visible). Unilateral cryptorchids
are fertile because the normally descended testis will produce
spermatozoa. However, it is not recommended that such animals
are used for breeding since cryptorchidism is probably genetic
in origin. Furthermore, because of the danger of tumour development
in the abdominal gonad, both testes are usually removed.
Persistent frenulum : During its development
the penis is attached to the wall of the prepuce by a fold
of tissue called the frenulum. This normally breaks down as
the animal matures. However, in rare cases this fold of tissue
persists and the animal is unable to protrude the penis and
complete intromission. The condition can easily be rectified
by a simple surgical operation.
Chromosomal abnormalities : It is now well
recognised that male tortoiseshell cats are almost always
infertile. The infertility is due to abnormalities in the
development of the seminiferous tubules and spermatogenesis.
Some of these males lack the normal secondary sexual characteristics
and show no libido. Cytogenic analysis of the chromosomes
of these animals have shown them to have an extra (X) chromosome
and a karyotype of 39XXY. Other male tortoiseshell cats have
been more male looking and these had multiple cell lines,
some of which were quite complex. Although such chromosomal
abnormalities have only been found in tortoiseshell toms,
there is no reason to suppose that other breeds of cats should
not occasionally have similar abnormalities. Although nothing
can be done to treat such animals, recognition of the condition
would save the animal from being subjected to numerous, ineffectual
Infections : Some foetal or neonatal infections
can lead to a maldevelopment of the reproductive system. For
example, testicular hypoplasia may be a consequence of an
early infection of panleucopaenia.
Trauma : Such things as scrotal bite wounds
will lead to local inflammation, heat and hence disruption
of spermatogenesis. The effects on fertility may last longer
than the visible effects of the wound. There is a time lag
of a number of days before the effects on the developing spermatozoa
are seen in ejaculated semen. Trauma resulting in a penile
haematoma may be a sequel to urethral obstruction.
problem said to be associated with long-haired cats is penile
hair rings. These develop because of the friction of the penile
spines against the perineal and dorsal hair of the female.
Usually, any such hair accumulation is removed by the tom
during grooming but if it is allowed to persist it may prohibit
intromission. When recognised, the problem can easily be rectified
by removing the hair ring.
Malnutrition : This is often secondary to
a prolonged illness and results inter alia in marked reduction
of spermatogenesis. The effect is usually reversible.
Obesity : At the other extreme, fat cats
often have poor libido although spermatogenesis is usually
normal. Cats fed on a high liver diet may develop testicular
degeneration because of hypervitaminosis A. The process can
be halted, although not reversed, by reducing the liver intake.
Overuse : In these cases there is no real
abnormality, it is just that the tom is being asked to use
up the semen faster than he can produce it. In such cases
libido will be maintained even after spermatozoa in the ejaculate
have fallen below levels adequate for conception.
Immature toms : Males reared in isolation
often do not mature until over a year old. Examination of
testosterone levels in such animals have shown them still
to be low. Furthermore, even mature toms, removed from the
stimulus of other animals, may suffer a temporary loss of
Debilitating diseases : Any chronic disease
will affect steroid production and secretion and hence reduce
Hypothyroidism : This condition produces
a generalised reduction on metabolic rate and all bodily processes
are retarded. However, this is reversible with suitable treatment.
Environment : Young males may be disturbed
by changes in environment or routine. This may be sufficient
to inhibit them making advances to queens even when they are
well in oestrus.
Queen : Aggressive behaviour on the part
of the female may discourage an inexperienced male. memories
of such behaviour may persist and the tom may be reluctant
to mount even a receptive female.
conclusion, fertility problems in the male usually present
either as a lack of libido or as a failure of conception,
but both can be caused by a number of factors.