Neutering Dogs: Effects on Joint Disorders and Cancers
in Golden Retrievers
Gretel Torres de la Riva1, Benjamin L. Hart2*, Thomas B. Farver1, Anita M. Oberbauer3,
Locksley L. McV Messam4, Neil Willits5, Lynette A. Hart1
1Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, California, United States of America,,
2Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California-Davis, Davis, California, United States of America,
3Department of Animal Science, College of Agriculture and Environmental Sciences, University of California-Davis, Davis, California, United States of America,
4Department of Public Health Sciences, School of Medicine, University of California-Davis, Davis, California, United States of America, 5Statistics Laboratory, Department
of Statistics, University of California-Davis, Davis, California, United States of America
In contrast to European countries, the overwhelming majority of dogs in the U.S. are neutered (including spaying), usually
done before one year of age. Given the importance of gonadal hormones in growth and development, this cultural contrast
invites an analysis of the multiple organ systems that may be adversely affected by neutering. Using a single breed-specific
dataset, the objective was to examine the variables of gender and age at the time of neutering versus leaving dogs
gonadally intact, on all diseases occurring with sufficient frequency for statistical analyses. Given its popularity and
vulnerability to various cancers and joint disorders, the Golden Retriever was chosen for this study. Veterinary hospital
records of 759 client-owned, intact and neutered female and male dogs, 1–8 years old, were examined for diagnoses of hip
dysplasia (HD), cranial cruciate ligament tear (CCL), lymphosarcoma (LSA), hemangiosarcoma (HSA), and mast cell tumor
(MCT). Patients were classified as intact, or neutered early (,12 mo) or late ($12 mo). Statistical analyses involved survival
analyses and incidence rate comparisons. Outcomes at the 5 percent level of significance are reported. Of early-neutered
males, 10 percent were diagnosed with HD, double the occurrence in intact males. There were no cases of CCL diagnosed in
intact males or females, but in early-neutered males and females the occurrences were 5 percent and 8 percent,
respectively. Almost 10 percent of early-neutered males were diagnosed with LSA, 3 times more than intact males. The
percentage of HSA cases in late-neutered females (about 8 percent) was 4 times more than intact and early-neutered
females. There were no cases of MCT in intact females, but the occurrence was nearly 6 percent in late-neutered females.
The results have health implications for Golden Retriever companion and service dogs, and for oncologists using dogs as
models of cancers that occur in humans.
Citation: Torres de la Riva G, Hart BL, Farver TB, Oberbauer AM, Messam LLM, et al. (2013) Neutering Dogs: Effects on Joint Disorders and Cancers in Golden
Retrievers. PLoS ONE 8(2): e55937. doi:10.1371/journal.pone.0055937
Editor: Bart O. Williams, Van Andel Institute, United States of America
Received August 3, 2012; Accepted January 4, 2013; Published February 13, 2013
Copyright: ? 2013 Torres de la Riva et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: Supported by the Canine Health Foundation (#01488-A) and the Center for Companion 330 Animal Health University of California, Davis (# 2009-54-F/
M). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: email@example.com
The overwhelming majority of companion dogs maintained in
the U.S. are spayed or castrated (both referred to herein as
neutered) . Increasingly in the U.S. neutering is being
performed early, demarcated in the present study as prior to one
year of age. The impetus for this widespread practice is
presumably pet population control, and is generally considered
responsible pet ownership. However, this societal practice in the
U.S. contrasts with the general attitudes in many European
countries, where neutering is commonly avoided and not generally
promoted by animal health authorities. For example, a study of
461 dogs in Sweden reported that 99 percent of the dogs were
gonadally intact , and an intact rate of 57 percent was reported
in a Hungarian study . In the United Kingdom, a 46 percent
intact rate was reported .
In the last decade, studies have pointed to some of the adverse
effects of neutering in dogs on several health parameters by
looking at one disease syndrome in one breed or in pooling data
from several breeds. With regard to cancers, a study on
osteosarcoma (OSA) in several breeds found a 2-fold increase in
occurrence in neutered dogs relative to intact dogs . Another
study on OSA, to explore the use of Rottweilers as a model for
OSA in humans, found that neutering prior to 1 year of age was
associated with an increased occurrence of OSA; 3–4 times that of
Hemangiosarcoma is a cancer that is affected by neutering in
females. A study of cardiac tumors in dogs found that cardiac HSA
for spayed females was greater than 4 times that of intact females
. A study on splenic HSA found the spayed females had more
than 2 times the risk of developing this tumor as intact females .
Neither of these studies separated early- versus late-spayed females
with regard to increased risk, and neither focused on just one
breed. A study on the epidemiology of LSA (lymphoma) in dogs,
for comparison with human lymphoma, found that intact females
had a significantly lower risk of developing this cancer than
neutered females or neutered males or intact males . Another
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cancer of concern is prostate cancer, which occurs in neutered
males about four times as frequently as in intact males . A
study on cutaneous mast cell tumors (MCT) in several dog breeds,
including the Golden Retriever, examined risk factors such as
breed, size, and neuter status. Although early versus late neutering
was not considered, the results showed a significant increase in
frequency of MCT in neutered females; four times greater than
that of intact females .
In contrast to the rather strong evidence for neutering males
and/or females as a risk factor for OSA, HSA, LSA, MCT, and
prostate cancer, evidence for neutering as protection against a dog
acquiring one or more cancers is weak. The most frequently
mentioned is mammary cancer (MC) . However, a recent
systematic review of published work on neutering and mammary
tumors found the evidence that neutering reduces the risk of
mammary neoplasia to be weak, at best .
With regard to joint disorders affected by neutering, one study
documents a 3-fold increase in excessive tibial plateau angle – a
known risk factor for development of CCL – in large dogs . A
paper on CCL found that, across all breeds, neutered males and
females were 2 to 3 times more likely than intact dogs to have this
disorder . In this study, with sexes combined, neutering
significantly increased the likelihood of HD by 17 percent over
that of intact dogs.
Given the widespread practice of neutering in the U.S.,
especially with public campaigns promoting early neutering, and
the contrast with neutering practices in other developed countries,
the objective of this project was to retrospectively examine the
effects of neutering on the risks of several diseases in the same
breed, distinguishing between males and females and early or late
neutering versus remaining intact using a single hospital database.
Because neutering can be expected to disrupt the normal
physiological developmental role of gonadal hormones on multiple
organ systems, one can envision the occurrence of disease
syndromes, including those listed below, to possibly be affected
by neutering as a function of gender and the age at which
neutering is performed. The study focused on the Golden
Retriever, which is one of the most popular breeds in the U.S.
and Europe. In this breed, HD, CCL, LSA, HSA, MCT, OSA,
and elbow dysplasia (ED) are listed as being of particular concern
No animal care and use committee approval was required
because, in conformity with campus policy, the only data used
were from retrospective veterinary hospital records. Upon
approval, faculty from the University of California, Davis
(UCD), School of Veterinary Medicine, are allowed restricted
use of the record system for research purposes. The final dataset
used for statistical analyses is available to qualified investigators,
upon request, from the corresponding author.
The dataset used in this study was obtained from the
computerized hospital record system (Veterinary Medical and
Administrative Computer System) of the Veterinary Medical
Teaching Hospital (VMTH) at UCD. The subjects included were
gonadally intact and neutered female and male Golden Retrievers,
1 to 8 years of age and admitted to the hospital between January 1,
2000 and December 31, 2009. Data from patients less than 12
months of age and 9 years or older were not considered.
Additional inclusion criteria were requirements for complete
information on date of birth, date of neutering (if neutered) and
date of diagnosis (or onset) of the joint disorder or cancer. Patients
were classified as intact or neutered; the neutering was sub-
classified as ‘‘early’’ if done before 12 months of age and ‘‘late’’ if
done at 12 months of age or older. For all neutered patients, the
neuter status at the time of each visit was reviewed to ensure that
neutering occurred prior to onset of the first clinical signs or
diagnosis of any disease of interest.
While the study set out to estimate incidence rates related to age
at the time of neutering, patients were diagnosed at different ages
and with differing durations of the disease as well as varying years
of exposure to the effects of gonadal hormone removal. For those
intact, early-neutered and late-neutered dogs diagnosed with a
disease, the age of diagnosis was recorded. Follow-up times were
recorded for each patient and determined by age of the dog at the
initial clinical signs or diagnosis, minus the age of the dog when
first included in the study. For dogs with no disease, follow-up
times were the age at the last visit to the VMTH minus the age
when the dog was first included in the study.
With the goal of obtaining a sample size sufficiently large for
statistical analysis, the database records were initially screened
using disease-related keywords to evaluate the frequency of
occurrence of HD, CCL, HSA, LSA, MCT, ED, OSA, and
MC. Extensive reviews of patient records were then performed for
specific evidence and information on each joint disorder or cancer
for every patient included in the study. Only diseases with at least
15 cases found using this screening were included in the study.
For all patients where age at time of neutering was not available
in the record, an effort was made to obtain the information by
telephone from the referring veterinarian. At the same time, age of
onset of the disease in question was also sought. If the information
was not available from the referring veterinarian, an attempt was
made to reach the dog owner for this information. In order to
optimize success in obtaining information, these efforts were
focused on patients born in 2000, or later, and that were admitted
to the VMTH between January 1, 2005 and December 31, 2009.
Table 1 defines the categories of diagnoses based on informa-
tion in the record of each case. A patient was considered as having
a disease of interest if the diagnosis was made at the VMTH or by
a referring veterinarian and later confirmed at the VMTH.
Patients clinically diagnosed with HD and/or CCL presented with
clinical signs such as difficulty standing up, lameness, or joint pain;
diagnosis was confirmed with radiographic evidence and/or
orthopedic physical examination. Clinical diagnoses of the various
cancers were accompanied by clinical signs such as enlarged
lymph nodes, lumps on the skin or presence of masses, and
confirmed by imaging, appropriate blood cell analyses, chemical
panels, histopathology and cytology. When a diagnosis was
suspected based on clinical signs, but the diagnostic tests were
inconclusive or not done, telephone calls were made to referring
veterinarians and owners to confirm the diagnosis. Lacking a
conclusive confirmation, the case was excluded from the analysis
for that specific joint disorder or cancer. Finally, body condition
scores (BCS), ranging from 1 to 9 and obtained from the patient
records (when available) were taken into account because BCS, as
an indication of weight on the joints, is considered to play a role in
the onset of these joint disorders [17,18]. Also, neutering has been
implicated in an increase in body weight, especially as indicated by
body condition score .
Kaplan-Meier survival analysis (K-M)  was used to estimate
survival curves for each disease and neuter status by gender, and
then log-rank and generalized Wilcoxon tests were used for post
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hoc comparisons between a set of two curves and thus to evaluate
differences in occurrence of the diseases of interest in each
comparison group. Incidence rate estimates (IR)  were used to
evaluate the rates of disease onset using time-at-risk of the disease,
in this case, dog-years at risk. Time-at-risk for a disease is the
duration of time each patient was observed prior to the disease
occurrence. For late-neutered dogs, time-at-risk prior to neutering
was used in the IR estimation for intact dogs and time observed
after neutering was used in the IR estimate for late-neutered dogs.
For each disease, rate ratios (RR) and their corresponding 95
percent confidence intervals (95% CI) were used to compare the
rates of acquiring each disease with regard to neuter status (i.e.,
intact vs. early neutered, intact vs. late-neutered, and early- vs.
late-neutered). To examine the role of BCS in the development of
HD and CCL, Cox proportional hazard (CPH) models were used,
in which both BCS and age at the time of neutering were included
as predictors. The resulting tests of the neutering effect are
adjusted for differences in BCS among the groups. Statistical level
of significance was set at the 5 percent level for all analyses.
Table 2 presents the sample size for each joint disorder or
cancer of patients meeting all inclusion criteria, separately for
males and females according to neuter status classification as to
intact, early-neutered, and late-neutered. The number of subjects
available for analyses of each disease varied because a patient
could be excluded from the analyses for one disease, if for
example, the diagnosis was made prior to one year of age or after 8
years, but would be included for analyses of all other diseases that
may occur within the ages 1 to 8 years. A case could be considered
as intact for one disease if onset was prior to neutering and as late-
neutered for another disease that may have occurred after
neutering. Meeting all inclusion criteria were 145 intact males,
178 early-neutered males, 72 late-neutered males, 122 intact
females, 172 early-neutered females, and 70 late-neutered females
(Table 2). The overall percentages of cases in the sample for the
five diseases affected by early and/or late neutering considered for
statistical analyses are presented in Figure 1 for males and in
Figure 2 for females. Mean follow-up times for all the diseases of
interest in intact, early-neutered and late-neutered dogs are listed
in Table 3.
As shown in Table 4, K-M survival analysis revealed that early
neutering was associated with an increased occurrence of HD,
CCL, and LSA. As shown in this table, comparisons of the IR
analyses reveal that late neutering was associated with the
subsequent occurrence of MCT and HSA in females. After the
initial screening, ED, OSA, and MC occurred in such low
numbers that statistical analyses were not feasible. MC was
diagnosed in only two cases in the total number of 364 females,
both in late-neutered females.
Perusal of Figure 1 and Table 4 reveals that HD in early-
neutered males, affecting 10.3 percent, was more than double the
proportion of intact males with the disorder, which was 5.1
percent, a significant difference (K-M: p,0.01). There was also a
significant difference between early and late neutering in males (K-
M: p,0.05). The mean ages of HD onset for intact, early-
neutered, and late-neutered male dogs were 4.4, 3.6, and 4.7
years, respectively. No difference was found between early-
neutered dogs with and without HD when compared with respect
to their BCS, (means 6.1 and 5.7, respectively; CPH: p=0.22). No
other comparisons of HD occurrence were significant; HD was not
increased in occurrence by early or later neutering in females
Cranial Cruciate Ligament Tear
As revealed in Figures 1 and 2, there was no occurrence of CCL
in either intact male or intact female dogs, or in late-neutered
females. However, in early-neutered dogs, the occurrence reached
5.1 percent in males and 7.7 percent in females, representing
significant differences in occurrence from both intact and late-
neutered dogs (K-M: p,0.05, Table 4). The mean age of CCL
onset in early-neutered males was 3.6 years and the single late-
neutered male dog diagnosed with CCL was 7.4 years. The mean
age of onset of CCL for early-neutered female dogs was 4.8 years.
For CCL, no differences were found between neutered males with
and without CCL with regards to their BCS (means 5.8 and 5.8
respectively; CPH: p =0.48). Likewise, no differences in mean
BCS were found between neutered females with and without CCL
(means 5.8 and 5.8 respectively; CHP: p =0.26).
Although the rates of occurrence of this disease were lower in
both male and female intact dogs, than in the early-neutered dogs,
the difference was statistically significant only in males. Early-
neutered males had nearly 3 times the occurrence of LSA as intact
males and no cases of LSA were observed in the late-neutered
males (K-M: p,0.05, Table 4, Figure 1). The mean ages of LSA
onset for intact and early-neutered male dogs were 5.3 and 5.8
Table 1. Categories used in determining diagnosis for joint disorders and cancers of interest in Golden Retrievers (1–8 years old)
admitted to the Veterinary Medical Hospital, University of California, Davis, from 2000–2009.
No diseaseNo evidence of a joint disorder or cancer of interest in the medical records
VMTH Diagnosed at the VMTH
Referring Veterinarian/VMTH Diagnosed by referring veterinarian and confirmed at the VMTH
Referring Veterinarian Diagnosed by referring veterinarian but no diagnostic tests done at the VMTH
Suspected Diagnosis was suspected based on clinical signs, but diagnostic tests were inconclusive or not done,
telephone calls were then made to referring veterinarians and owners to confirm diagnosis, unconfirmed
cases were excluded from analysis for the suspected joint disorder or cancer
Invalid Diagnosed prior to January 2000 or after December 2009 and before 1 year of age or 9 years of age and
older were excluded from analysis for the specific joint disorder or cancer
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Figure 1. Percentages and number of cases over the total sample size for each neutering status group; intact and neutered early or
late for male Golden Retrievers (1–8 years old) diagnosed with hip dysplasia (HD), cranial cruciate ligament tear (CCL),
lymphosarcoma (LSA), hemangiosarcoma (HSA), and/or mast cell tumor (MCT) at the Veterinary Medical Teaching Hospital of the
University of California, Davis, from 2000–2009. For HD and LSA, the differences between early-neutered and intact or late-neutered groups
were statistically significant (K-M), as were differences for CCL between intact and early-neutered groups.
Figure 2. Percentages and number of cases over the total sample size for each neutering status group; intact and neutered early or
late for female Golden Retrievers (1–8 years old) diagnosed with hip dysplasia (HD), cranial cruciate ligament tear (CCL),
lymphosarcoma (LSA), hemangiosarcoma (HSA), and/or mast cell tumor (MCT) at the Veterinary Medical Teaching Hospital of the
University of California, Davis, from 2000–2009. For CCL the difference between intact and early-neutered was statistically significant (K-M).
For HSA, the differences between early and late-neutered and intact and late-neutered groups were statistically significant (RR), as were differences
for MCT between early and late-neutered groups. A similar statistical comparison for late neutering and intact groups was not possible for MCT
because there were 0 cases in the intact group.
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Figure 2 reveals that late-neutered females at 7.4 percent were
diagnosed with HSA over 4 times more frequently than intact
females with 1.6 percent and early-neutered females with 1.8
percent, both significant differences (RR=6.10, 95% CI =1.18,
31.37 and RR=7.48, 95% CI=1.79, 31.30). The mean ages of
HSA onset for intact, early-neutered, and late-neutered female
dogs were 6.4, 7.6, and 3.2 years, respectively. No differences were
apparent in males with regard to neutering and the occurrence of
HSA (Figure 1).
Mast Cell Tumor
Figure 2 portrays the findings regarding MCT in female dogs,
which did not occur in intact females, but was diagnosed in 2.3
percent of early-neutered females and 5.7 percent of late-neutered
females. The RR cannot be estimated when disease occurrence is
zero in one comparison group, as in the intact females. However,
the wide difference in MCT occurrence between intact and late-
neutered females was meaningful, given that the MCT occurrence
in late neutered females and early neutered females was significant
(RR=4.46, 95% CI=1.11, 17.82). The mean ages of MCT onset
for the early-neutered and late-neutered female dogs were 6.2 and
6.5 years, respectively. No differences were found in the
occurrence of MCT in male Golden Retrievers (Figure 1).
This is the first study of the effects of neutering on an array of
joint disorders and cancers in the same breed of dog, using a single
database and examining the variables of gender and early and late
neutering versus leaving the dogs gonadally intact. No cases of MC
were diagnosed in intact females in this study. This finding is
partially explained by the relatively low frequency in which MC is
diagnosed in Golden Retrievers . While this finding contrasts
with the general concern expressed about the risk of MC in
gonadally intact females [12,21,22], it is consistent with the recent
findings from a systematic meta-analysis finding a weak link, if
any, between neutering and reduced risk of MC .
For all five diseases analyzed in the present study, the disease
rates in males and/or females were significantly increased when
neutering was performed early and/or late. When a disease
occurred in intact dogs, the occurrence was typically one-fourth to
one-half that of early- and/or late-neutered dogs. When no intact
dogs were diagnosed with a disease, such as with CCL in both
sexes and MCT in females, the occurrence in early- and/or late-
neutered dogs ranged between 4 and 8 percent of the sample.
The results are consistent with all of the previously reported
findings, mentioned in the introduction, of neutering in males
and/or females in increasing the likelihood of HSA, LSA, MCT
and CCL by about the same degree. However, this is the first
study to specifically report an effect of late neutering on MCT and
HSA. In the case of HD, which was doubled in the early-neutered
males in the present study, the previous study reported a
significant increase by only 17 percent in neutered dogs grouped
together . These contrasting differences with the effects of
neutering on HD profile the value of the approach of the present
study in focusing on just one breed and separating out the effects of
gender and early versus late neutering.
An important point to make is that the results of this study,
being breed-specific, with regard to the effects of early and late
neutering cannot be extrapolated to other breeds, or dogs in
general. Because of breed-specific vulnerabilities, certain diseases
being affected by neutering in Golden Retrievers may not occur in
other breeds. By the same token, different joint disorders or
cancers may be increased in likelihood in a different breed. A full
understanding of the disease conditions affected by neutering
across an array of different breeds will require several more breed-
A logical question to ask with regard to the joint disorders of
HD and CCL is if those neutered dogs diagnosed with the disorder
Table 2. Total sample sizes obtained for male and female
Golden Retrievers (1–8 years old) admitted to the Veterinary
Medical Hospital, University of California, Davis, from 2000–
2009 according to neuter status classification: intact, early-
neutered, and late-neutered.
DiseaseTotalIntact Neutered Early Neutered Late
HD 359 138156 65
LSA391 144 17671
MCT 393144 17871
Total*395 145178 72
CCL360 122 16969
HAS 361123** 17068
*Total number of dogs meeting all inclusion criteria.
**Includes patients that were diagnosed with a disease of interest prior to
eventual late neutering.
Table 3. Mean follow-up times for male and female Golden
Retrievers (1–8 years old) admitted to the Veterinary Medical
Hospital, University of California, Davis, from 2000–2009 by
disease status for each neuter category.
DiseaseIntact Early NeuteredLate Neutered
No Disease 2.12 3.16 1.77
CCL NA 3.37NA
LSA 3.36 3.67NA
NA= Not applicable because there were no cases of the specific joint disorder
or cancer in that neuter category.
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were carrying relatively more weight on their joints, which may
have predisposed them to the disorder. Therefore, once an effect
of early neutering was found with regard to HD (males) and CCL
(males and females), the CPH model was applied to reexamine the
effect of early neutering, after adjusting for differences in BCS.
While neutering is expected to lead to a greater gain in body
weight than in intact dogs [17,18], the BCS of early-neutered dogs
with the disorders and the early neutered comparison groups
without the disorders were not significantly different – and, in fact
quite similar – indicating that weight on the joint was not a major
determinant in the occurrence of these joint disorders. Using the
CPH model to compare early-neutered with intact dogs, for both
HD and CCL, neither neutering status nor BCS was significant,
indicating that the two factors are fairly highly confounded. This
implies that the occurrence of HD and CCL in early-neutered
dogs is a combined function of the effect of neutering on growth
plates, as well as the increase in weight on the joints brought on by
neutering. As mentioned, when only early-neutered dogs with and
without HD or CCL were compared with respect to their BCS, no
differences were found between early-neutered males with and
without these joint disorders.
As for the pathophysiological reasons for the joint disorders, one
can point to the role of gonadal hormones in controlling the
closure of bone growth plates [23,24]. An atypical growth plate
closure, resulting from the absence of gonadal hormones, may
increase the chance of a clinically apparent joint disorder, such as
HD, CCL, and possibly ED. Confounding factors that may
influence the nature of a neuter-related joint disorder are the
breed-specific gender vulnerabilities, including growth rate differ-
ences, as well as the timing of growth plate closure, which occurs
more quickly in males than in females. In the males of this study,
the occurrence of HD was doubled in the cases with early
androgen removal as compared with intact males, but in females,
removal of the ovaries did not appear to be associated with an
increased likelihood of HD. This presumably reflects the effect of
gender on growth-plate development. However, growth-plate
disturbance in both males and females seems to have played a role
in the occurrence of CCL in early-neutered dogs. This joint
disorder was not diagnosed in either intact males or females. The
mean age of CCL onset was later in life than in HD (about 4 years
and 2 years, respectively).
The role of gonadal hormone removal in the occurrence of
various cancers appears to be more complicated. The effects of
early neutering on the increased rate of LSA, especially in males,
contrast with the effects of late neutering in females on MCT and
HSA. The effects of late neutering associated with the occurrence
of MCT and HSA in females bring up the issue of the role of
timing of estrogen alteration. One possibility is suggested by the
role of estrogen removal and microsatellite instability in colon
cancer development in women. Based on clinical findings, it is
speculated that estrogen secretion may sensitize the pathways
involved in microsatellite instability. While estrogen remains in the
system, it is protective against microsatellite instability-positive
cancer cell activation and reduces the risk of colon cancer.
However, upon estrogen removal, microsatellite instability-positive
cancer cells become activated resulting in an increased occurrence
of colon cancer .
Applying this concept to the role of neutering on HSA and
MCT in female dogs, this study suggests that with early neutering,
before an estrous period, the cells that could become neoplastic are
not sensitized to estrogen and neutering would not affect disease
occurrence. However, after exposure to estrogen through several
estrous cycles, potentially neoplastic cells could be sensitized, but
as long as the female is left intact, the estrogen is protective. Then,
if neutered after several estrous cycles, the estrogen-sensitized cells
could become neoplastic, hence a higher rate of HSA and
especially MCT in late-neutered than early-neutered females.
Obviously, much remains to be learned that could be explored
with a large database with regard to the specific effects of estrogen
in these cancers.
The findings presented here are clinically relevant in two
realms. For dog owners and service dogs trainers and caretakers
using the popular Golden Retriever as the service dog, the study
points to the importance of acquiring information needed for
deciding upon if and when to neuter. Specifically for Golden
Retrievers, neutering males well beyond puberty should avoid the
problems of increased rates of occurrence of HD, CCL, and LSA
and should not bring on any major increase in the rates of HSA
and MCT (at least before nine years of age). However, the
possibility that age-related cognitive decline could be accelerated
by neutering should be noted . For females, the timing of
neutering is more problematical because early neutering signifi-
cantly increases the incidence rate of CCL from near zero to
Table 4. Summary of some Kaplan-Meier post hoc comparisons using log-rank (LR) and generalized Wilcoxon (W) tests for male
and female Golden Retrievers (1–8 years old) admitted to the Veterinary Medical Hospital, University of California, Davis, from
DiseaseGender Test typep (early vs. intact)p (early vs. late)p (late vs. intact)
HD LR 0.04NSNS
W 0.01 0.04 NS
CCL LR0.003 0.02NS
W 0.004 0.01NS
CCLLR 0.0010.001 NS
W 0.006 0.004NS
NS= Statistically non significant.
PLOS ONE | www.plosone.org6February 2013 | Volume 8 | Issue 2 | e55937
almost 8 percent, and late neutering increases the rates of HSA to Download full-text
4 times that of the 1.6 percent rate for intact females and to 5.7
percent for MCT, which was not diagnosed in intact females.
The findings of this study also have important implications for
investigators looking for canine models for research on various
forms of cancer [27,28]. For some cancers of interest, not only may
breeds vary in predisposition but also the possibility of interactions
between gender, gonadal hormone influences, and timing of
gonadal hormone alteration (if any), should be taken into account
in selecting the model and in investigating causal factors to be
Special thanks are extended to Marty Bryant, Abigail Thigpen, Alexandra
Brindle, Katherine Sylwester and Alisha Tran.
Interpreting results and editing manuscript: AMO. Conceived and
designed the experiments: BLH LAH GT. Performed the experiments:
GT LAH BLH. Analyzed the data: GT TBF LLM NW. Wrote the paper:
GT BLH LAH.
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PLOS ONE | www.plosone.org7 February 2013 | Volume 8 | Issue 2 | e55937