Neutering
terms and attitudes: Note:
Neuter applies to either sex.
Neutering of dogs has been performed
for a number of years, and in some countries is a widely accepted
practice. The Guide Dogs for the Blind neuter dogs not earmarked for
breeding, and many of us share our homes with neutered pets.
Neutering of pet dogs is often recommended using vague terms such as it
‘improves pet health and behaviour’ [1, 2], though this is not
universally correct (eg [3-8]). There is often scant mention of
possible benefits outside that of reducing pet numbers, nor discussion of
possible downsides. Some disadvantages are minor, some may be of
larger importance. The following may be seen as “politically
incorrect” in that it is not a wholesale endorsement of neutering.
This is because like most things in biology, I find the pros and cons of
neutering are neither black nor white. In some ways, our
veterinarians may be caught in between – veterinarians are often
presented with cases of pyometra or behavioural problems – which
neutering would have in the case of pyometra, and may have in the case of
behavioural issues prevented (would also prevent nasty tempered dogs being
used in breeding). So promoting neutering may actually reduce the
potential cases they would see – even though some people see promotion
of neutering as a money-making ploy by the veterinary profession.
Generally, the terms used are spayed,
neutered, castrated, gonadectomised or desexed. Neutering,
castration, desexing and gonadectomy can apply to either sex. Spay
is reserved for females, which have an ovariohysterectomy (ovaries and
uterus are removed), or ovariectomy (ovaries are removed). In males,
permanent sterilisation is most commonly achieved through removal of
testes (sometimes called orchiectomy or orchidectomy). There was a
product on the market in the USA that is injected into testes to achieve
permanent sterilization, but I believe it may now be difficult to obtain.
In Australia and some other countries there is also a product available
for reversible suppression of reproductive function of male dogs (yes,
dogs have been used to sire litters after the effect of the product has
‘worn off’). It is available as an implant like a microchip and
renders a dog infertile for at least 6 months, with newer implants
effective for longer periods in the pipeline [9].
Early age neutering has largely come
about through efforts to reduce unwanted pet numbers in the USA, mainly
because a proportion of young animals rehomed through shelters never
presented to be neutered, despite having been provided with vouchers for
the procedure to be performed. Sometimes early age neutering is
called prepubertal or prepuberal neutering. The terms prepubertal/prepuberal
may be confusing, as although they mean sterilization of sexually immature
animals (before the first oestrus, or before spermatozoa are present in an
ejaculate), this can be at different physiologic ages in different breeds
of dog. Age at puberty may vary from anywhere from 6 months in
smaller breeds to up to 24 months of age in larger breed dogs.
Husbandry (nutrition, kenneling) may also alter this timeframe [10].
Root Kustritz [11] defines early neutering or prepuberal gonadectomy as
occurring in pups up to 14 weeks of age. Others use ‘early age’
to refer to neutering performed earlier than the more traditional age of
around 6 months (eg [12-14]). (The reported benefits/risks of early
age neutering a presented separately, below.)
Not all countries have similar rates
of, or attitudes towards, neutering. Thus, discussions as to the
pros and cons of neutering, especially in young animals, are largely
confined to the USA where general policy is that dogs are neutered before
leaving animal shelters. This is supported by the assertion that
“dogs and cats benefit from gonadectomy performed at any age” [11].
In general, neutering of dogs is less common in Europe than in North
America. Neutering unless for medical reasons was prohibited in
Sweden until 1988. In one study of Swedish dogs born 1993-1995,
only1-3% had been neutered [15]. Until fairly recently spaying
except on medical grounds was also prohibited in Norway [16]. Thus
data comparing health of intact versus neutered animals is not necessarily
available everywhere even when studies have been undertaken.
Some people’s
decisions to spay/neuter, or at what age to neuter may be different
depending upon their breed and its predispositions (also note that some
studies are unable to provide breed related information as there were
insufficient dogs of a breed available in the study in order to make sound
statistical analyses from which to draw meaningful information).
Yes neutering will 100% guarantee your
male will not get testicular cancer, nor your bitch uterine cancer or
ovarian cancer, because these are the bits which are removed – if
they’re not there, they can’t develop cancer. And nor can
infections of these organs occur (when a complete ovariohysterectomy is
performed), nor can your dog or bitch sire or whelp a litter. And
there are not many 100% guarantees in biology! On a population level
general statements can be made regarding any health benefit/risk, but on
an individual basis (ie, *your* dog), there are generally no guarantees.
Some people have asked for a quick
summary of the pros and cons of neutering, and this is below.
Further explanations are below the summary.
Advantages
of spay or neuter
•
Eliminates risk of testicular cancer (most are benign in behaviour)
• Reduces risk of mammary cancer (if performed before 2.5 years
of age)
• Reduces risk of pyometra (uterine infection)
• Eliminates risk of uterine tumours (given uterus is
removed)
• Eliminates risk of ovarian cancer
• Reduces risk of prostatic hyperplasia and inflammation
• Reduces risk of benign perianal tumours in dogs
• Reduces urine marking, mounting. May reduce roaming
Disadvantages
of spay or neuter
• Decreased life span
•
Increases risk of urinary incontinence (in both bitches and dogs)
• Increases risk of obesity
• Increases risk of osteosarcoma (bone cancer)
• Increases risk of prostatic cancer
• Increases risk of bladder cancer
• Increases risk of cardiac haemangiosarcoma
• Increases risk of splenic haemangiosarcoma in spayed bitches
• Increases risk of cholangiocarcinoma (cancer of bile ducts) in
spayed bitches
• Increases risk of cranial cruciate ligament injury
• Increases risk of patellar luxation in small- and medium-sized
dogs
• Increases risk of adverse vaccine reactions
• Increases risk of myasthenia gravis in spayed bitches
• Increases risk of pancreatitis in spayed bitches
• Increases risk of aggression, fearfulness
• Increases cognitive impairment in aged dogs already showing
signs of disease
• Increases risk of benign perianal tumours in spayed bitches
• Increases risk of peri-vulvar dermatitis, vaginitis, cystitis
and recurrent urinary tract infections in early-age spayed bitches
Surgical
complications:Neutering of dogs
and bitches is a surgical procedure. All surgery carries risk, but
the risk of major complications following neuter surgery is low – which
is probably self-explanatory given how often the procedure is performed.
Complications were reported to occur more frequently in dogs older than 1
year of age than those neutered at a younger age [17]. Overall
complication rates are approximately 20% [17, 18], with major
complications occurring in up to 4% of cases [17, 19], and death in less
than 0.1% of cases [17].
Testicular cancer:
Testicular cancers with malignant (nasty) behaviour in dogs are uncommon.
Many older dogs have tumours in their testes, and these go largely
undetected [20]. Testes that are cryptorchid (don’t descend) have
something like 13.6 times increased risk of developing a cancer, and it is
recommended these be removed [21].
Prostatic cancer and
prostatic problems: Neutering will prevent the vast
majority of prostatic problems that arise in dogs (infections and symptoms
associated with hyperplasia (a benign enlargement)), but, contrary to some
reported benefits of neutering eg [1], it may increase the risk of
development of prostatic cancer by up to 4.3 times that of an intact dog
[22, 23,119]. An older study reported that a higher prevalence of
prostatic cancer was not found in neutered dogs compared with intact dogs
“than could be explained by the number of neutered males in the
population” [24]. The conflicting information aside, canine
prostatic carcinoma is an uncommon neoplasm. How uncommon/common is
difficult to determine, with reports ranging from no cases diagnosed in
one ten year Japanese study [25] to an incidence of less than 1% of cases
[26, 27]. That said, of 17 cases of cancer of the prostate I saw in
a 5 year period, only 5 had gone to necropsy (or post mortem, as we tend
to call it here). Some of these 17 cases were only diagnosed post
mortem. Only ~ 40% of dogs which had been diagnosed with prostatic
tumours had a biopsy or necropsy confirm the condition (diagnosis was made
on prostatic wash or massage). So, there is “more of it about”
than the rates of 0-<1% in necropsy studies would indicate.
Generally, prostate cancer is described as a disease dogs aged around 10.
One paper included two Vizslas in its study population of 35 dogs with
prostatic cancer (dogs attended U Penn 1997 - 2001) [23]. This is
the only paper that I have seen that has included Vizslas in its study
group.
Dogs that are neutered do not develop benign prostatic
hyperplasia (BPH). BPH is a hormone-dependent disorder, relying on
testosterone. The testes produce around 95% of the testosterone in
the male dog. So without the testes, the prostate doesn’t develop
hyperplasia. BPH occurs so frequently in aged dogs that it might be
considered an age-related physiologic process – BPH occurs in 50-100% of
dogs over the age of 5, though it is generally not a clinically
significant problem, with only around 1.5% of dogs displaying clinical
signs [22].
Female reproductive tract
cancer and infection: Spaying a bitch will reduce the
occurrence of uterine infection (pyometra) and prevent development of
uterine cancer. Uterine tumours are very uncommon (0.3-0.4% of all
canine tumours), the majority of which are benign [21]. Pyometra can
be life threatening. Incidence and risk rates for pyometra are
confounded by spay rates. One text quotes pyometra as occurring in
around 0.6% of bitches, increasing to 66% of bitches over 9. Another
study identified 9% of female admissions were for pyometra (reviewed by
[28]). In Sweden where approximately 7% of bitches are spayed, risk
of pyometra differed with age, breed and where the dogs lived [29].
Where dogs live may influence the proportion of dogs receiving veterinary
care. Approximately 25% of insured Swedish dogs develop pyometra by
age 10, with age-related differences observed between breeds.
Approximately 4% of cases resulted in death [30]. In a colony of
Beagles, 15% of bitches over the age of 4 developed pyometra [31].
‘Stump pyometra’ may occur in spayed bitches, thus spaying does not
completely eliminate the risk of pyometra.
Ovarian tumours, which are also uncommon, (accounting up to
1.2% of tumours, of which approximately 17% are benign) and for which
incidence or risk rates will be altered by spay rates, will also be
prevented as long as the bitch also has her ovaries removed [21, 32].
Mammary cancer:
Mammary tumours in bitches are reported to be the most common growth to
arise in bitches. Incidence increases with age. Only about
half of these are malignant growths. And of these, around half of
the malignancies are likely to recur or spread to other organs. It
is generally reported that the risk of mammary tumours occurring is
related to spaying, and to the age of the bitch when the spay procedure is
performed. The risk of developing mammary cancer is reported to be
significantly reduced if bitches are spayed before 2.5 years of age [33].
Risks compared with risk in intact bitches (not all of whom develop
mammary tumours) increase from 0.5%, to 8%, to 26%, depending upon whether
a bitch is spayed before her first heat, second, or third season and
thereafter, respectively [34]. In comparison, a UK study found no
difference in the odds ratio for a diagnosis of mammary neoplasia from
intact or spayed bitches, but age at spay was not known [35].
Interestingly, it has been reported that age at diagnosis for intact and
spayed bitches were not significantly different [33] – which is not the
expected behaviour of a tumour that is believed to be hormonally
initiated. The risk of mammary tumour in spayed dogs is also reduced
in those that are thin when aged 9-12 months of age [33].
It is generally agreed that mammary
lumps are like skin lumps – in that they are more easily detected
(visualised/palpated) and likely to be excised than tumours occurring in
internal organs, so this also skews the true incidence rates as a
proportion of all tumours.
Under the umbrella term ‘mammary
carcinoma’ there is more than one type of cancer. They are all
called ‘mammary carcinoma’, because that’s where they arise.
The different types can have different origins within the mammary tissue
(different cell of origin), and varying biologic behaviour. For
example, although the least common type of carcinoma occurring in canine
mammary tissue is a carcinosarcoma, it is the type most likely to spread
and recur. Not all the studies on mammary tumours in dogs use the
same criteria to include cases for study. For instance, the
Schneider et al paper [34] above was based on adenocarcinomas and mixed
mammary tumours. Sonnenschein et al [33] excluded mixed mammary
tumours and sarcomas from their study. Note also, that in different
countries exogenous hormones are often used more widely to control
oestrous patterns in the bitch, and these may alter the risk of
development of mammary lumps.
Increased risk for mammary tumours in
one breed over another varies by study. Several including Egenvall
et al [36] have reported increased risk for English Springer spaniels.
Dobermans and Boxers were also identified as at increased risk.
It has also been reported that spaying a bitch within 2
years of removal of her mammary carcinoma increases survival compared with
the survival of intact bitches and with the survival of bitches spayed
more than 2 years prior to tumour removal [37]. The authors of this
study wrote; “The risk reduction for developing mammary tumors by
performing ovariohysterectomy after 2.5 years is minimal, and the positive
effect of ovariohysterectomy is strongest when performed concurrent with
tumour surgery. Should we advise our clients that if they do not
spay their dogs before the second oestrus, it is better to wait until they
are much older or till they develop mammary gland tumors?” [37].
In contrast, another recent study did not find hormonal status or time of
spay influenced survival for bitches with malignant mammary tumours [38].
Bladder cancer:
The risk for development of transitional cell carcinoma of
the bladder is 4 times greater for neutered animals than for intact
animals. Around 2% of cancers in dogs are bladder cancer, with some
breeds at increased risk (eg Scottish terriers have a 19 times increased
risk over mixed breed dogs). An increased prevalence of bladder
cancer has been seen at teaching hospitals in recent years [39].
Bone cancer, bones and
ligaments: In a study of 683 Rottweilers,
a breed at risk for development of osteosarcoma (bone cancer), the “Risk
for bone sarcoma was significantly influenced by age at gonadectomy.
Male and female dogs that underwent gonadectomy before 1 year of age had
an approximate one in four lifetime risk for bone sarcoma and were
significantly more likely to develop bone sarcoma than dogs that were
sexually intact” [40]. When neutered before 1 year of age, dogs
were 3.8 times, and bitches 3.1 times more likely to develop an
osteosarcoma than an intact dog or bitch. This risk was independent
of size and weight of the adult dogs [40]. A separate study on
various breeds reported that the risk of osteosarcoma doubles with
neutering [4].
Neutering is
associated with twice the increased risk of cranial cruciate ligament
rupture (CCL) [41-43]. Age at spay was not associated with
prevalence of ruptures, though age at spay was not known for many dogs
[43]. Association between obesity following neutering and CCL was
not able to be determined [43]. A later study on dogs less than 2
years of age found heavier dogs were more likely to have CCL [41].
Vizslas were not considered a breed at increased risk of CCL [43].
Neutering is
associated with a 3-fold increase in risk of patellar luxation in small-
and medium-sized dogs, though
this may be related to age as the neutered dogs were older than intact
dogs, and risk of patellar luxation also increases with age [44].
Boxer dogs that had been neutered at
least 6 months before examination were 1.5 times more likely to have
clinical hip dysplasia than intact Boxers (a 50% increase). This
clinical presentation was attributed to increased body weight
post-neutering [45].
In the Airedale Club of America health
survey, bitches and dogs with a musculoskeletal disorder were more likely
to be neutered than intact, but it is not clear if these animals were
neutered to remove them from a breeding programme, or whether neutering
predisposed the dogs to the conditions [46].
Studies in male Beagles found a loss of bone volume
(reduced bone formation compared with resorption) in neutered dogs [47].
Although these results suggest male dogs are a suitable model for
osteoporosis, other studies have found bitches to be unsuitable for such
studies due to lack of sustained bone loss [48, 49].
Perianal tumours:
Benign perianal gland tumours (perianal adenoma) are
androgen sensitive (many regress when a dog is castrated), and thus, the
majority, but not all, occur in intact males. Reported as the most
common epithelial skin tumour in dogs [50], the risk of perianal tumours
is also increased in spayed females, and it is suggested oestrogen is
protective against their development [51]. Goldschmidt and Shofer
[50] saw thirteen cases of this benign tumour in Vizslas, and they
reported a 1.8 times increased risk of this condition in the breed.
There are conflicting reports
concerning perianal gland adenocarcinoma (which occurs far less frequently
than benign perianal gland lesions, comprising approximately 1% of skin
tumours [50]); some authors have noted no gender differences, whilst other
studies found the majority occur in intact males [51, 52], or that when
compared with intact bitches, neutered bitches are at increased risk [51].
Although anal sac adenocarcinoma (occur as approx 2% of
skin tumours in dogs) is considered to arise independent of hormonal
influence, the majority of affected dogs have been neutered [50, 52].
A recent study of 113 cases found no gender bias [53].
Other
tumours: Neutering
increases the risk of splenic haemangiosarcomas in bitches (2 times risk
in spayed over intact) [54], and cardiac haemangiosarcomas in dogs and in
bitches (spayed females > 5 times greater relative risk than intact
females; and “The risk for castrated males was slightly greater than
that for intact males, which had 2.4 times the relative risk of intact
females”) [55]. Spayed bitches have a 1.5 times increased risk of
cholangiocarcinoma (bile duct cancer) than do intact bitches.
Cholangiocarcinoma is uncommon, comprising less than 1% of tumours seen in
dogs [56].
A decrease in odds of tumours (benign and malignant) from
the mouth/pharynx and reproductive systems was found for neutered dogs of
both sexes, over intact dogs [35]. Part of this should not be
surprising given the information concerning testicular tumours and mammary
tumours. The study however also found no difference in the odds
ratio for a diagnosis of mammary neoplasia from intact or spayed bitches
(age at spay was not known).
Incontinence:
Neutering increases the risk of urinary
incontinence in both bitches and dogs [5, 57]. Spayed bitches are up
to 7.8 times more likely to develop urinary incontinence [5].
Incontinence may affect up to 20% of bitches, with breed dispositions
(especially large breeds) and geographical differences observed – one
study reporting up to 65% of Boxer bitches developing post-spay
incontinence, whilst only 10% of German Shepherd bitches were affected,
whilst in the USA [58, 59] and Netherlands, Dobermanns are at increased
risk [60]. Neutering also substantially increases the risk of
incontinence in Airedales and Irish setter bitches [46, 61].
The condition is uncommon in dogs (one study reported 1/122
dogs neutered for behavioural reasons developed incontinence following
neuter surgery [62]), but unlike in many bitches, responds poorly to
treatment [57, 59]. When bitches are spayed the levels of
gonadotropin hormones (follicle stimulating hormone and luteinising
hormone) increase as the feedback loop for the hypothalamic-pituitary
system is no longer present. The levels of these hormones are now
being thought to play a role in development of incontinence in spayed
bitches, but the associations are not clearly understood as yet –
gonadotropin levels in spayed incontinent bitches are significantly lower
than levels in spayed continent bitches [58].
Diseases with possible
immune-mediated mechanisms: The effect of
neutering and risk of hypothyroidism is unclear. Neutering has been
associated with a significant increase in risk of hypothyroidism [63, 64].
In Golden retrievers there appears to be an association between neutering
and hypothyroidism [65]. In contrast, a study in the UK did not find
neuter status a risk factor for hypothyroidism [66]. It has recently
been reported that certain major histocompatibility complex (MHC) antigens
may be associated with hypothyroidism in some breeds [67, 68], though how
hormonal status may/ not influence this is not known.
It
has been reported that neutering increases the risk diabetes in neutered
males, though the findings have not been universal in all populations
studied [69]. Spayed bitches are more likely to be diagnosed with
pure red cell aplasia [70], and compared with other University hospital
dogs, one study reported neutered dogs and bitches were over-represented
in cases with immune-mediated haemolytic anaemia [71]. MHC antigens
have also recently been reported to be associated with both diabetes and
haemolytic anaemia [72, 73], and as with hypothyroidism, how hormones may
influence the development of disease is not known.
Compared with intact, spayed bitches have been found to be
at increased risk of developing myasthenia gravis [74]. This study
included six affected Vizslas, and it was reported that compared with
mixed breed dogs, Vizslas had a 3.3 times increased risk of myasthenia
gravis.
Vaccination:Following vaccination (excluding dogs that also
received heartworm vaccination), neutered dogs and bitches were found to
be at increased risk (27-38% compared with intact animals) of adverse
reactions, none of which were life threatening. This was attributed
to alterations in immune function following neutering. The risk was
inversely related to the dog’s weight (smaller dogs/breeds more likely
to have an adverse reaction than larger dogs), and the risk was greatest
in dogs of 1-3 years of age compared with dogs of other ages [75].
Following rabies vaccination both intact and young animals were less
likely to produce appropriate levels of antibodies for entry into the UK.
There were also differences in sero-conversion rates depending upon the
breed of dog and what country the dog was from [76].
Increased incidence of parvoviral enteritis has been
reported in shelter animals neutered before 24 weeks of age when compared
with those neutered over the age of 24 weeks, though it was postulated
that differences in rate of infection were attributable to different
shelter practices [13]. Neutered males are less likely to contract
parvovirus enteritis than intact dogs [77]. The authors attributed
this to neutered dogs being less likely to roam, and thus come into
contact with infectious agents.
Obesity:
Several studies have reported neutered dogs were
significantly more likely to be overweight or obese than of normal weight,
and the number of obese and overweight dogs increased as their age
increased [78-80]. Obesity after neutering was found to be strongly
influenced by breed [79, 80], and after adjusting for increasing weight
with increased age, significantly more gundogs were obese or overweight
after neutering compared with intact gundogs [79]. Similarly, Golden
retriever bitches neutered at < 1 year of age are significantly heavier
than those neutered at age 1 or more [65], and neutered Wirehaired
Pointing Griffons (WPGs) weigh more than intact WPGs [81]. Other
studies have been less emphatic; less than half the 122 males in one study
had increased weight following neutering [62], whilst in another study 25
of 48 dogs that were castrated had an increased bodyweight [82].
Spayed bitches are more likely to have increased
‘indiscriminate appetite’ (eats rapidly, eats any commercial dog food,
eats rubbish) than intact bitches [83] or increased food intake [84],
which probably accounts for the observations that neutered bitches gain
weight [84] and are twice as likely to be obese [85]. In one study,
the weight gain in bitches was not related to increased deposition of
subcutaneous fat [84]. In a 15-month study by Salmeri et al [86],
although a trend for increased body fat was found in neutered animals, no
statistical difference in obesity occurrence was attributable to
neutering. It is unknown what the long-term result might have been (ie
years). Others however, have reported body weight increases
post-spay due to increased body fat [87]. In a separate study that
followed neutered pets for 4 years, owners did not perceive animals
neutered either before or after 24 weeks of age as being obese, though the
author does acknowledge owners might not be the best judge of obesity in
their pets [13].
Longevity:
Information on the effect of neutering on longevity has
only recently taken into account at what age dogs were neutered. It
is generally claimed that neutered dogs and bitches live longer [1, 2].
One report found neutered bitches lived longer than intact females [88],
and whilst there was no statistical difference, neutered dogs and bitches
tended to live longer [89] (also, see below regarding Golden retrievers
and height/early age neutering). Most studies however fail to take
into account the age at neutering, and that with increasing age more dogs
in a population are likely to be neutered. Thus, intact versus
neutered represents census data at that time point, rather than lifetime
risk. In a 10-year study of Boxers, when the population was simply
considered as neutered or intact, being neutered was associated with a
decreased risk of death. When age at neutering was considered,
neutered was associated with increased risk of death [3].
Behaviour:
Regarding other people’s experience with changes in
behaviour following neutering, it would be wise to bear in mind the
following; “One cannot extrapolate from experience with one or two
dogs or cats in predicting the effects of castration or ovariectomy”
[90].
In
contrast with the oft claimed behavioural benefits of neutering to
‘improve pet behaviour’ [1], where neutered pets ‘become more
affectionate and become better companions’ [1, 2], several reports have
found otherwise [6, 7, 83], with both breed and sex differences noted [6].
An open access web-based survey reported neutered dogs and bitches more
aggressive to owners and were more aggressive towards, or fearful of,
other dogs, and were more sensitive to touch than intact animals.
Breed and sex differences of touch sensitivity were noted [6]. A
breed Club based survey by the same author found similar; spayed bitches
were more aggressive towards strangers, more fearful, and more sensitive
to touch than intact bitches. “For most behaviours,
spaying/neutering was associated with worse behavior, contrary to
conventional wisdom. A few behaviours (e.g., energy level, urine
marking) were reduced in spayed/neutered dogs" [6].
Increased aggression towards strangers has previously been reported [7].
Neutering of males often reduces the
sexually dimorphic behaviours – urine marking, roaming and mounting [62,
91, 92]. If a dog has repeated or learned these behaviours over some
time, it is often suggested neutering will be less likely to be
successful. However neither age of the dog nor duration of the
problem behaviour is predictive as to whether castration will have a
beneficial effect as changes in behaviour do not occur in all dogs
following neutering [82, 90-92]. In a study of 42 dogs with
behaviour problems, roaming was the behaviour reported as being most
affected by neutering – in 15/16 cases [92]. Another study of
roaming in 25 dogs found no alteration in 80% of dogs whose roaming was
not induced by bitches in oestrus, and an increase occurred post-neuter
for 4% of dogs. In dogs roaming because of a bitch in oestrus, a
reduction occurred in 64% of dogs [62]. Five of ten dogs which were
urine marking in the house had the behaviour decline in the house
following neutering, but marking when taken for a walk did not alter [92].
Other studies have reported reduction of urine marking inside the house
for 69% of dogs [62], and no decrease in urine marking for 35/48 (73%)
dogs [82]. Ten of 15 dogs which were reported as mounting other
people or animals had the behaviour decline after neutering [92], whilst
another study found improvement in all six dogs studied with this
behavioural problem [82]. It has also been reported that 5/48 male
dogs appeared more affectionate post-castration [82].
Regarding aggression, in one study
neutering in five out of eight dogs reduced aggression towards other dogs
[92], whilst another study reported 6/9 dogs that were aggressive had a
post-castration reduction in aggression, and of 48 dogs that were
castrated (includes the 9 aggressive dogs), two had an increase in
aggressive behaviour, and two had an increase in barking [82].
Another study found intermale aggression was reduced in 57% of dogs, but
it also increased in 4% [62]. Neutering did not alter territorial
aggression in eight dogs, nor fear-induced aggression in four dogs [92].
Perhaps it may be that neutering does not change behaviour for some male
dogs as much as it changes their environment so to speak – because they
are no longer smelling like intact male dogs to other male dogs, other
dogs react different to them and they are challenged less often? And
speaking of smelling like intact males, or not – 6% of neutered males
became attractive to intact male dogs [62].
A recent study of one year old dogs
found bitches more likely to be fearful, and males aggressive, and that
these behaviours were more extreme in neutered animals [93]. In dogs
over a year of age, a significant association between aggression and
neuter status has also been reported – the odds ratio for a member of
the household being bitten by their dog were 3.23 for neutered males and
2.13 for neutered bitches, but age and reasons for neutering were not
known [94]. Guy et al [94] also cited previous studies (Wright &
Nesselwrote, 1987 and [95] both papers in the journal Applied Animal
Behaviour Science) which found a disproportionate percentage of spayed
bitches were presented for aggression problems compared to their relative
frequency in the referral population. Spaying may increase dominance
aggression tendencies, especially in those bitches that are already
aggressive [83]. The risk of an increase in aggression was reported
to be greatest in bitches who were spayed at less than one year of age
[83]. A study of Cocker Spaniels (which excluded dogs and bitches
that were neutered once showing signs of aggression) found that neutered
bitches were more likely to show aggression towards children in the
household than were intact bitches [95]. German shepherd bitches who
were spayed between 5 and 10 months of age were more reactive to approach
by strangers than non-neutered bitches of the same age [96]. An
Australian study of owner-companion dog interactions recently reported
neutered dogs “were considered to be more nervous or timid than sexually
intact dogs”, they were also rated as less anxious and engaged in fewer
destructive behaviours” [97].
In English Springer Spaniels (ESS),
neutering is associated with increased risk of biting (either sex);
neutered males were more aggressive than intact males in 14 of 18 contexts
(eg hug, stare, remove special food), and spayed females were more
aggressive than intact females in 10 contexts (eg nudge on bed or couch,
push off furniture). As I’ve suggested with the examples in
parentheses, these contexts were not necessarily the same for dogs and
bitches. Neutered of either sex were more likely to have bitten than
intact ESS [98]. Male Cocker Spaniels neutered before showing any
aggressive signs were no more likely to be aggressive in a variety of
different situations than were intact males [95].
Intact dogs and bitches are a third as
likely to have separation anxiety as neutered ones [99]. This is
also supported by the observation that in Europe where the percentage of
dogs that are neutered is lower, a lower proportion of behaviour referrals
are for separation anxiety.
Reports on general activity levels following neutering
vary. Spayed bitches were reported to be less energetic than intact
bitches [6, 7]. Following castration 8/48 dogs were lethargic or
appeared calmer (14/48 dogs) [82], though it was noted the dogs were
generally around 8 years of age, and this may be age- rather than
castration-related. Other studies have reported neutered dogs and
bitches were less anxious and engaged in fewer destructive behaviours
[97], or that they were more active and excitable than sexually intact
dogs and bitches [86].
Cognitive impairment:
Regarding age/longevity, cancers are not the
only consideration to be made; testosterone slows the progression of
behavioural changes associated with cognitive impairment in aging dogs
already showing clinical signs of disease [100]. Unfortunately
insufficient sexually intact bitches were available in the study to
evaluate the effect of neutering on bitches. Whilst by itself
inappropriate elimination as frequently occurs with cognitive dysfunction
is not life threatening, this problem may result in euthanasia of the dog.
Other conditions:An increased risk of pancreatitis has been
reported for neutered bitches [101, 102], and
for neutered dogs in one study [101].
Perineal
hernias are most likely to occur in intact, middle-aged dogs.Dogs with perineal hernias have lower concentrations of androgen
receptors in the muscles associated with the herniation.Castration is often used as part of the treatment to reduce
prostatic size, and thus possible straining that might be associated with
enlargement of the prostate [82].
And
whilst not directly health related; some dogs can develop skin and coat
changes (thin, dry skin and woolly coat) after neutering , with an increase in hair growth (3/48) or
change in coat colour (1/48) observed in dogs that were castrated [82].This is more pronounced in coated breeds such as spaniels,
golden retrievers, Irish setters (eg [103-105]).The ill-understood coat condition observed in double coated breeds
and variously referred to as ‘black skin disease’, ‘coat funk’,
adult-onset growth hormone deficiency, growth hormone-responsive alopecia,
castration-responsive alopecia, biopsy-responsive alopecia, congenital
adrenal hyperplasia-like syndrome and alopecia X is not as some names might suggest, a condition that necessarily
improves, nor maintains improvement upon neutering.It has recently been suggested the term hair cycle arrest be used
for this condition [106].
Early-age neutering:
Surgical
complications:It has been reported that dogs and bitches
neutered below 12 weeks of age have significantly fewer minor surgical
complications than those neutered aged over 24 weeks [107].
Gender
characteristics:Neutering of dogs and bitches before sexual
maturity can inhibit the development of ‘gender characteristics’, such
as broader bones in legs and skull and broader chest in dogs, and of
muscular development.Because
the hormonal surge of puberty causes the growth plates in the bones to
close, dogs neutered before puberty grow taller than they would have
otherwise as the period of growth is prolonged (but the growth rate is
unaltered [86]).This does not mean your
Vizsla will grow to the size of an Irish Wolfhound!The taller stature may also be accentuated by the reduced
muscle mass in neutered animals.Salmeri
et al [86] found that for dogs neutered at 7 weeks and 7 months of age when
compared against intact litter mates, the younger a dog was neutered, the
taller the dog became.In
bitches however, the bone length was not significantly different between
intact bitches and those neutered at 7 months of age, but was between
those neutered at 7 weeks and all the other bitches.Thus,
whilst slight alterations in eventual height and body mass may be
irrelevant in a dog of unknown parentage obtained from a shelter, people
who choose to neuter their purebred may prefer to defer neutering a very
young animal.
Longevity,
cancer and obesity:Healthwise,
Canine Companions for Independence (provide trained assistance dogs) found
that early age neutered dogs had increased incidence of osteosarcoma,
haemangiosarcoma, and obesity [8].
Not early age neutering specifically, but related
to neutering at a young age and resultant increased height and/or weight;
in Golden retrievers, “Both bitches and dogs neutered at < 1 year of
age were significantly taller as adults than those neutered at > or = 1
year of age or intact animals.”Further,
“Among bitches and dogs, the taller the animal as an adult, the shorter
the lifespan.”[65].Similarly, the Wirehaired
Pointing Griffon survey also reported taller and heavier WPG bitches died
at an earlier age than shorter and lighter bitches [81], and taller and heavier
Akitas were more likely to develop neoplasia [108].One study reported that early-age neutered dogs were less
likely to be overweight than those neutered at later ages [14].(In relation to weight, diet restriction in Labrador
retrievers delays the onset of arthritis and increases median life span
compared to litter mates whose feed intake was not restricted [109].)
Bones
and ligaments:Early-age
neutered dogs have increased incidence of orthopaedic problems (type not
specified) [8],
and hip dysplasia (CHD) [14].Similarly, a correlation between increased incidence of CHD and
increased time for growth plate closure has been reported in Labradors [110].Although rates of CHD were increased in early neutered dogs, one
study found the disease was significantly less severe than in dogs that
were neutered at a later age; dogs with hip dysplasia that had been
neutered at 5.5 months or older were “3 times as likely to be
euthanatized for the condition as those with hip dysplasia and
gonadectomized before 5.5 months of age.” [14].This study was done on dogs obtained from a shelter – not a
population of dogs that would normally be screened for CHD.I assume therefore, the dogs presented with clinical signs.In contrast, one study that followed early-age neutered pets
for a 4-year period found no statistical difference in CHD rates between
pre-pubertal (< 24 weeks of age), and traditional age (>/= 24 weeks
of age) neutered pets [13].
Again, relating
to neutering at a young age and resultant increased height/weight; Akita
dogs (not bitches) “with any musculoskeletal disorder were 2-times as
likely to be in the highest weight/height category than were dogs never
diagnosed with a musculoskeletal disease.” [108].
Incontinence:Age of spay - pre-pubertal, and
traditional age - has been reported not to influence the development of
urinary incontinence in bitches [13,
59].One study observed 20/206 early spayed bitches developed
incontinence, and when compared with a different earlier study that
reported around 20% of bitches spayed after their first oestrus developed
incontinence, ascertained that the risk of incontinence in early-spayed
bitches was lower [111].The clinical signs in bitches spayed prior to their first oestrus
were however, increased, though the authors consider that because most
bitches respond to treatment, and that incontinence risk is lower, “This
relative disadvantage of early spaying is negligible when compared with
the benefits, such as lower incidence of urinary incontinence and the
protection against mammary tumours.” [111].
In contrast, an
increased risk of urinary incontinence in bitches spayed before, compared
with after their first heat cycle at the 10% level of significance, but
not at the more conventional 5% level has been reported [5].This is supported by increased incontinence seen in early-age
spayed assistance dogs [8],
and a study on early neutering referred to earlier [14],
where a scale was noticed for incontinence risk and age at spaying –
bitches neutered at less than 3 months of age were at greater risk of
incontinence than those neutered at 3 months of age or more, and also in
the WPG study where; “..the average age at neuter for neutered bitches
with urinary incontinence was lower compared with the average age at
neuter for bitches with no history of urinary incontinence.This raises a concern about the current movement to neuter
dogs at a much earlier age.” [81].
Peri-vulvar
dermatitis/vaginitis: With early-age neutering external genitalia
remain infantile in appearance [86].Peri-vulvar dermatitis has
been associated with an infantile vulva, but the reports of its
significance vary.Increased
rates of peri-vulvar dermatitis [59,
112-114] and/or vaginitis (reviewed
in [10]), [114] have been reported in neutered compared with intact bitches, but the
dermatitis may be uncommon [112], and was not demonstrated in a study of early-age and traditional age
neutered bitches [86].Conversely recent
preliminary studies found a higher incidence of recessed vulva,
peri-vulvar dermatitis, vaginitis, and recurrent urinary tract infections
in spayed than in intact bitches, and the incidence was significantly
higher in bitches spayed before puberty compared with those spayed later [114].
Cystitis:
Spain
et al [14] also reported an increased risk of cystitis in early neutered bitches.In a health survey of Old English Sheepdogs, 6/7 cases of cystitis
in male dogs were in neutered males (total of 275 neutered males) and
35/48 cases of cystitis in bitches were in those who had been spayed
(total 200 spayed bitches) [115].All
cases of vaginitis occurred in spayed bitches (40/200 spayed bitches and
0/253 intact bitches) [115].
Behaviour:
Prepubertal
neutered dogs were more likely to succeed in becoming guide dogs than
littermates neutered at a later age Canine
Companions for Independence who provide assistance dogs found early age
neutered dogs were more likely to fail training [8], and “ovariectomized police dogs have been reported to show unsatisfactory
work performance when compared with sexually intact females” [117]
Perhaps
these differences relate to the nature of the required tasks?I do not know how the assessment was performed on
the Guide Dogs – whether there was a statistically significant
difference, nor if other factors were considered, etc – as it was just
referencing a personal communication.
Behaviour-wise, Spain et al [14] reported “escaping considered a serious problem
declined with decreasing age at gonadectomy”.Increased rates of noise phobias and sexual behaviours were
observed in early-age neutered dogs, whilst separation anxiety was
decreased in early-age neutered dogs, though the authors suggested that
these 3 results may represent Type I (false positive) errors.
Other
conditions: The
long-term study of early age neutered dogs included 167 dogs that had more
than 10 years follow-up (median period of the study was 4.5 years).Rare occurrences of autoimmune disorders, chronic renal failure,
diabetes mellitus, mammary tumours, pancreatitis, hepatic disease,
patellar luxation and urinary stones were reported
The
risks and benefits (e.g. reduce risk of mammary cancer, increased risk of
cranial cruciate ligament injuries, etc) that have been reported for dogs
neutered at later ages should also still apply.
Someone I
'know' by email in northern California has said that the clinic near her
no longer recommends neutering of males at 6 months, or necessarily at all
if they are in a responsible home.If
they are going to be done, then they wait until around a year, and the
same age for bitches.The
pendulum swinging?
And if you planned to
do serious performance events with your dog – apart from the increased
risk of cruciate ligament injury, there is reduced muscle mass in the
absence of testosterone – not exactly performance enhancing ;/It would be interesting to know the effect of this in old age
– are neutered pets more prone to arthritic pain as their muscles are
less well developed and able to support the joints?
… and one last
thing, some people have suggested vasectomy might be acceptable for the
purposes of sterilization for owners who do not want their dog’s testes
removed.Studies on dogs
before and after vasectomy reported that following vasectomy there was an
increase in aggressiveness between some dogs and also greater libido [118].Conditions such as roaming, mounting and marking which are
associated with androgens may still be expected to still occur.
Should I spay or