risk from castration and spay (ohe)

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Spay and Snarl: A Possible Connection Between Ovariohysterectomy and Increased Aggression

Reviewer Jacqui Neilson, DVM, BS, DACVB
Publication Citation


Title: Behavioural effects of ovariohysterectomy on bitches
Author: O'Farrell V, Peachy E
Journal: J Small Anim Pract
Volume: 31
Number:
Pages: 595-598
Date: 1990


Purpose of Study


Background
While surgical sterilization is often performed in male dogs to control objectionable behaviors, ovariohysterectomy (OHE) is usually done in female dogs to control reproductive functions (eg, heat cycles and pregnancy). The effects of this procedure on other behaviors has not been investigated extensively.

Hypothesis
Female dogs may have an increase in aggressive behavior subsequent to OHE.

Findings of Study


Study Design
The investigators interviewed two groups of dog owners: those that had female dogs that were going to be spayed and those that did not plan on spaying their female dogs (ie, the control group). The control group was matched for breed and age against the spay group. The spay group owners were given a questionnaire about their dog’s behavior at the time of spay surgery and 6 months later. The control group owners were given the two questionnaires at the same times as the spay group owners. The investigators looked for differences in behaviors between the spay group and the control group dogs.

Study Results
Significant differences were found between control and spay group dogs in dominance aggression and indiscriminate appetite. Spayed dogs were more likely to have an increase in dominance aggression towards family members between the first and second interviews compared with the control group, while the control group dogs were likely to have a decrease in this type of aggression. The spay group had an increase in indiscriminate appetite (eg, eating meals quickly, eating any commercial dog food, and ingesting other food-associated items such as trash) between interview one and two while the control group dogs had a decrease in this activity.

Commentary


Design Evaluation
The double questionnaire format (one at the time of procedure and another 6 months later) warrants merit because the study did not rely on the owner's long-term memory to recall particular behavior patterns in the dog at a single interview after the procedure was completed. The use of a control group is also commendable since it helps to identify those behaviors that are changing independent of surgery (eg, behaviors changing with maturity). Although the attempt to manage some variables with a control group are admirable, it cannot replace the ideal control group (ie, sham-OHE group). For ethical reasons, it may not be practical to do sham surgery on client-owned dogs. However, a sham-OHE group would more accurately address the effects of anesthesia, surgery, and recovery that the dog experiences during OHE.

The study questioned the owners on certain behaviors and then grouped these behaviors into categories. For example, the behaviors that constituted "dominance aggression towards family members" included dog threatens if disturbed when resting, dog threatens family members, dog threatens when groomed, and dog threatens when something is taken away. Although these specific triggers listed are often seen in a diagnosis of dominance aggression, it takes a much more involved historical profile to arrive at this diagnosis. For example, a dog that threatens when groomed may be doing so from a motivation of pain-related aggression, not dominance aggression. The diagnostic categories should be interpreted with caution.

Finally, no indication was included in the paper as to what stage of the heat cycle the dog was in at the time of OHE.

Results Evaluation
From the data, it appears that the group most likely to show a disproportionate increase in aggression are female dogs <11 months of age at the time of OHE that already showed some aggression before surgical alteration. Ovariohysterectomy does not appear to induce aggression in female dogs, but it may lead to exacerbation of dominance aggression in younger female dogs. This apparent increase in aggression may be due to a sudden change in hormonal status associated with OHE.

The authors did observe that the control group (ie, nonspayed dogs) had received significantly more progestogen at the time of the first interview than did the spay group dogs. Frequency of administration of this drug was not reported between the first and second interview. Did this exogenous hormonal administration have an effect on the behavior of the nonspayed dogs?

Clinical Application
In a female dog <11 months of age who is exhibiting signs consistent with dominance aggression, it may be wise to delay the surgery until she is mature. Of course, you will have to weigh the potential risk of an unwanted pregnancy against the potential for increased aggression.

Weight control should be proactively discussed with all pet owners.

Questions Raised
What is the impact of routine OHE on behavior?
Should we postpone OHE in young dogs (ie, <11 months of age) showing signs of dominance-type aggression?
Should we more carefully control the diet of spayed bitches to prevent obesity?


Summary
Ovariohysterectomy may be associated with the exacerbation of existing dominance-type aggression in young female dogs. In a female dog <11 months of age who is exhibiting signs consistent with dominance aggression, it may be wise to delay the surgery until she is mature. Ovariohysterectomy also may be associated with an increase in indiscriminate eating habits.
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Current veterinary therapy X! page 876 under a section called relationship of incontinence to neutering

incidence and breed predisposition

A retrospective study of 412 spayed bitches revealed an incidence of 20.1%. There appears to be a strong correlation between body weight and the incidence of incontinence. Of bitches with a body weight of less than 20 kg, only 9.3% were incontinent, whereas in bitches with a body weight of more than 20kg, the incidence was 30.9%. Boxers showed the highest incidence (65%)

this study was from arnold s et al incontinentia urinae bei der kastreirten hundin haufigkekeit and rassedisposition, schweiz arch. tierheilkd 131:259,1989
*****
Title: [Urinary incontinence in castrated bitches. Part 1: Significance, clinical aspects and etiopathogenesis]
Source: JOURNALS ABSTRACT (Schweiz Arch Tierheilkd 139[6]:271-6 1997)
Author(s): Arnold S
Address (URL):
--------------------------------------------------------------------------------

Acquired urinary incontinence occurs in 20% of spayed dogs and there exists a strong correlation between body weight and the risk of urinary incontinence. Bitches with a body weight of more than 20 kg have a risk of 30% white smaller dogs have a risk of 10%. A particular breed disposition exists in Boxers in which 65% are affected. Other breeds with a more than average disposition for urinary incontinence are Dobermans and Giant Schnauzers. Urinary incontinence due to spaying manifests itself mainly while the dogs are sleeping. The cause is a urethral sphincter incompetence which can be verified by a urethral pressure profile (UPP). The microtransducer method proved to be a suitable method for urodynamic studies. It could be demonstrated that the urethral closure pressure is significantly lower in incontinent bitches (4.6 +/- 2.3 cm H2O) than in continent bitches (18.6 +/- 10.5 cm H2O). In addition, the urethral closure pressure for continent bitches dropped significantly within 12 months after surgery. Histological examination revealed that the functional urethral closure cannot be explained by the extent of discernible structures of the urethral wall as seen by light microscopy.
*****
*****
Effect of Gonadectomy on Subsequent Development of Age-Related Cognitive Impairment in Dogs
J Am Vet Med Assoc 219[1]:51-56 Jul 1'01 Cohort Study 52 Refs
Benjamin L. Hart, DVM, PhD, DACVB
Behavior Service, Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA 95616
OBJECTIVE: To determine whether gonadectomy predisposes dogs to development of age-related behavioral changes linked to cognitive impairment. DESIGN: Cohort study. ANIMALS: 29 sexually intact male dogs, 63 spayed female dogs, and 47 castrated male dogs 11 to 14 years old. PROCEDURE: Information on possible impairments in 4 behavioral categories linked to cognitive impairment (orientation in the home and yard, social interactions, house training, and sleep-wake cycle) was obtained from owners of the dogs by use of a structured telephone interview format. A second interview was performed 12 to 18 months after the initial interview, and differences in responses were evaluated. RESULTS: Sexually intact male dogs were significantly less likely than neutered dogs to progress from mild impairment (i.e., impairment in 1 category) to severe impairment (i.e., impairment in > 2 categories) during the time between the first and second interviews. This difference was not attributable to differences in ages of the dogs, duration of follow-up, or the owners' perceptions of the dogs' overall health. CONCLUSIONS & CLINICAL RELEVANCE: Results suggest that the presence of circulating testosterone in aging sexually intact male dogs may slow the progression of cognitive impairment, at least among dogs that already have signs of mild impairment. Estrogens would be expected to have a similar protective role in sexually intact female dogs; unfortunately, too few sexually intact female dogs were available for inclusion in the study to test this hypothesis. There may be a need to evaluate possible methods for counteracting the effects of loss of sex hormones in gonadectomized dogs.
***
Effects of feeding regimens on bodyweight, composition and condition score in cats following ovariohysterectomy.
J Small Anim Pract 42[9]:433-8 2001 Sep

Harper EJ, Stack DM, Watson TD, Moxham G
The effects of ovariohysterectomy on bodyweight, composition and condition score were evaluated in 49 cats that were fed ad libitum and 11 cats that had their food allowances controlled with the aim of maintaining a stable bodyweight. In cats fed ad libitum, bodyweight increased by an average of 31 per cent in the 12 months following ovariohysterectomy compared with 3.1 per cent over the 12 months before surgery, and this was largely due to increased body fat content. There was no difference in weight gain between cats fed dry or canned foods, but weight gain was inversely related to age and bodyweight at the time of neutering. Mean bodyweight increased by 7.5 per cent in the controlled feeding group, compared with 3.6 per cent over the 12 months before surgery, and individual bodyweights were maintained to within 10 per cent of pre-neutering values in nine cats. The other two cats experienced substantial weight gain (+20 per cent and +36 per cent), despite being fed only 40 kcal/kg/day. There were no significant changes in body composition of cats with controlled dietary allowances and their condition scores were significantly lower than those of cats fed ad libitum. The results confirm a link between ovariohysterectomy and the development of obesity in cats with free access to food, and indicate that substantial reductions in energy intake are required to prevent weight gain in such cats.
*****
Benign esophageal stricture in the dog and cat: a retrospective study of 20 cases.
Can J Vet Res 66[1]:55-9 2002 Jan
Adamama-Moraitou KK, Rallis TS, Prassinos NN, Galatos AD
Twenty animals with benign esophageal strictures are presented. Most of the esophageal strictures were thought to be related to gastroesophageal reflux during ovariohysterectomy and were located at the distal portion of the thoracic esophagus (caudal to the base of the heart). For the dilation procedure, the endoscope tip or a balloon catheter was used and the outcome was generally considered to be good. The endoscope tip was an adequate instrument for dilation in some cases.

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http://www.ncbi.nlm.nih.gov:80/entrez/q ... db=PubMed&
list_uids=12433723&dopt=Abstract

Full-text available for a fee at:
http://cebp.aacrjournals.org/cgi/conten ... 11/11/1434

Endogenous Gonadal Hormone Exposure and Bone Sarcoma Risk.
Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters DJ.
Cancer Epidemiol Biomarkers Prev 2002 Nov;11(11):1434-1440

Although experimental and clinical evidence suggest that endogenous sex
hormones influence bone sarcoma genesis, the hypothesis has not been
adequately tested in an appropriate animal model. We conducted a historical
cohort study of Rottweiler dogs because they frequently undergo elective
gonadectomy and spontaneously develop appendicular bone sarcomas, which
mimic the biological behavior of the osteosarcomas that affect children and
adolescents. Data were collected by questionnaire from owners of 683
Rottweiler dogs living in North America. To determine whether there was an
association between endogenous sex hormones and risk of bone sarcoma,
relative risk (RR) of incidence rates and hazard ratios for bone sarcoma
were calculated for dogs subdivided on the basis of lifetime gonadal hormone
exposure. Bone sarcoma was diagnosed in 12.6% of dogs in this cohort during
71,004 dog-months follow-up. 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 [RR +/-95% CI = 3.8 (1.5-9.2)
for males; RR +/-95% CI = 3.1 (1.1-8.3) for females]. chi(2) test for trend
showed a highly significant inverse dose-response relationship between
duration of lifetime gonadal exposure and incidence rate of bone sarcoma (P
= 0.008 for males, P = 0.006 for females). This association was independent
of adult height or body weight. We conclude that the subset of Rottweiler
dogs that undergo early gonadectomy represent a unique, highly accessible
target population to further study the gene:environment interactions that
determine bone sarcoma risk and to test whether interventions can inhibit
the spontaneous development of bone sarcoma.

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OVARIECTOMY OR OVARIOHYSTERECTOMY - COMPARISON OF LONG-TERM EFFECTS

Neutering of bitches is a routine surgery in small animal practice. If
ovariectomy or ovariohysterectomy is performed, is a common point of
discussion. In this study, 135 dog owners answered questionnaires concerning
their bitches neutered years ago with either ovariectomy or
ovariohysterectomy.


The present study compares long-term effects of ovariectomy versus
ovariohysterectomy in the bitch. Questionnaires were sent to 264 owners of
bitches, in which ovariectomy or ovariohysterctomy had been performed as a
routine neutering procedure 8-11 years earlier. Complete data were available
for 69 bitches of the ovariectomy group and for 66 bitches from the
ovariohysterectomy group. There were no indications that endometritis had
developed in bitches of the ovariectomy group. None of the bitches was
sexually attractive to male dogs after neutering. The occurrence of a clear
to white vaginal discharge was reported in two bitches of each group, but
none of these four bitches appeared to be ill during the period when the
discharge was present. Furthermore, with the exception of urinary
incontinence, no problems were reported that could be related to the
surgical neutering. Six of the ovariecto- mized bitches and nine of the
ovariohysterctomized bitches eventually developed urinary incontinence. Of
these 15 bitches (11 %), 12 weighed more than 20 kg. Bouvier des Flandres
bitches were at a higher risk of developing urinary incontinence than were
those of the other breeds. The possibility that the urinary incontinence was
due at least in part to other conditions must be considered, since eight of
the bitches were 9 years or older before urinary incontinence occurred and
seven of the incontinent bitches also had polyuria or polydipsia. There were
no significant differences in the incidence of urogential problems listed
above between the bitches of the ovariectomy and ovariohysterectomy group.
It is hypothetized that a uterine disease such as CEH-endometritis cannot
develop after complete ovariectomy, unless progestagens are administerd. The
results of this study indicate that ovariectomy does not inrease the risk of
CEH-endometritis or other complications in comparison with
ovariohysterctomy.
It is concluded that there is no indication for removing the uterus during
routine neutering in healthy bitches. On the contrary, ovariectomy should be
considered the procedure of choice.


Source: Okkens, AC, Kooistra, HS, Nickel, RF (2003): Comparison of long-term
effects of ovariectomy versus ovariohysterectomy in bitches
In: Der Praktische Tierarzt, 2003, Vol 84, Iss 2, pp 98-101

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J Am Vet Med Assoc 224[3]:380-387 Feb 1'04 Retrospective Study 38 Refs
* C. Victor Spain, DVM, PhD; Janet M. Scarlett, DVM, PhD; Katherine LIB. Houpt, VMD, PhD, DACVB
* Philadelphia Department of Public Health, Division of Disease Control, 500 S Broad St, Philadelphia, PA 19146
OBJECTIVE: To evaluate the long-term risks and benefits of early-age gonadectomy, compared with traditional-age gonadectomy, among dogs adopted from a large animal shelter.

DESIGN: Retrospective cohort study.

ANIMALS: 1,842 dogs.

PROCEDURE: Dogs underwent gonadectomy and were adopted from an animal shelter before 1 year of age; follow-up was available for as long as 11 years after surgery. Adopters completed a questionnaire about their dogs' behavior and medical history. When possible, the dogs' veterinary records were reviewed. Associations between the occurrence of 56 medical and behavioral conditions and dogs' age at gonadectomy were evaluated.

RESULTS: Among female dogs, early-age gonadectomy was associated with increased rate of cystitis and decreasing age at gonadectomy was associated with increased rate of urinary incontinence. Among male and female dogs with early-age gonadectomy, hip dysplasia, noise phobias, and sexual behaviors were increased, whereas obesity, separation anxiety, escaping behaviors, inappropriate elimination when frightened, and relinquishment for any reason were decreased

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From Pubmed:

1: J Reprod Fertil Suppl. 2001;57:233-6. Related Articles, Links


The relationship of urinary incontinence to early spaying in bitches.

Stocklin-Gautschi NM, Hassig M, Reichler IM, Hubler M, Arnold S.

Department of Reproduction, Veterinary Faculty of Zurich,
Winterthurerstrasse 260, CH-8057 Zurich, Switzerland.

It is still controversial whether a bitch should be spayed before or after
the first oestrus. It would be desirable to spay bitches at an age that
would minimize the side effects of neutering. With regard to the risk of
mammary tumours, early spaying must be recommended because the incidence of
tumours is reduced considerably. The aim of the present study was to
determine whether early spaying also reduces the risk of urinary
incontinence. The owners of 206 bitches that had been spayed before their
first oestrus and for at least 3 years were questioned on the occurrence of
urinary incontinence as a result of spaying. At the time of the enquiry the
average age of the bitches was 6.5 years, and the average age at the time of
surgery was 7.1 months. Urinary incontinence after spaying occurred in 9.7%
of bitches. This incidence is approximately half that of spaying after the
first oestrus. Urinary incontinence affected 12.5% of bitches that were of a
large body weight (> 20 kg body weight) and 5.1% of bitches that were of a
small body weight (< 20 kg body weight). The surgical procedure (ovariectomy
versus ovariohysterectomy) had no influence on the incidence, or on the
period between spaying and the occurrence of urinary incontinence. Urinary
incontinence occurred on average at 2 years and 10 months after surgery and
occurred each day, while the animals were awake or during sleep. However,
compared with late spaying the clinical signs of urinary From Pubmed:

1: J Reprod Fertil Suppl. 2001;57:233-6. Related Articles, Links


The relationship of urinary incontinence to early spaying in bitches.

Stocklin-Gautschi NM, Hassig M, Reichler IM, Hubler M, Arnold S.

Department of Reproduction, Veterinary Faculty of Zurich,
Winterthurerstrasse 260, CH-8057 Zurich, Switzerland.

It is still controversial whether a bitch should be spayed before or after
the first oestrus. It would be desirable to spay bitches at an age that
would minimize the side effects of neutering. With regard to the risk of
mammary tumours, early spaying must be recommended because the incidence of
tumours is reduced considerably. The aim of the present study was to
determine whether early spaying also reduces the risk of urinary
incontinence. The owners of 206 bitches that had been spayed before their
first oestrus and for at least 3 years were questioned on the occurrence of
urinary incontinence as a result of spaying. At the time of the enquiry the
average age of the bitches was 6.5 years, and the average age at the time of
surgery was 7.1 months. Urinary incontinence after spaying occurred in 9.7%
of bitches. This incidence is approximately half that of spaying after the
first oestrus. Urinary incontinence affected 12.5% of bitches that were of a
large body weight (> 20 kg body weight) and 5.1% of bitches that were of a
small body weight (< 20 kg body weight). The surgical procedure (ovariectomy
versus ovariohysterectomy) had no influence on the incidence, or on the
period between spaying and the occurrence of urinary incontinence. Urinary
incontinence occurred on average at 2 years and 10 months after surgery and
occurred each day, while the animals were awake or during sleep. However,
compared with late spaying the clinical signs of urinary incontinence were
more distinct after early spaying.

PMID: 11787155 [PubMed - indexed for MEDLINE]
.

PMID: 11787155 [PubMed - indexed for MEDLINE]

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The following capsule report appeared in the January 2005 edition of NAVC Clinician's Brief (p 37). Early Gonadectomy - Think again

Little is known about risk factors for osteosarcoma, although age-specific incidence associates it with pubertal growth spurt. Osteosarcoma in dogs closely resembles its human counterpart in location (wide extremity of long bone), aggressive behavior, pulmonary metastases, and mortality. Spontaneous canine osteosarcoma is estimated at 10,000 cases per year in the U.S. and its association with body size (mostly large- and giant-breed dogs) is well documented, although no studies have measured body size within the same breed. Humans do not undergo gonadectomy, whereas neutered pet dogs provide a unique population for study of the effects of endogenous sex hormones. Rottweilers, at high risk for bone sarcoma, were chosen for this historical cohort study. Age at gonadectomy and adult height/body weight were examined to determine significant risk factors. Data were collected by questionnaire from owners of 683 rottweilers in North America; 12.6% of dogs were diagnosed with osteosarcoma. Results showed a highly significant inverse dose-response relationship between duration of exposure to endogenous gonadal hormones: longer exposures (i.e., later neutering) were associated with less risk for osteosarcoma. Although females were more often diagnosed with bone sarcoma than males, the difference was not significant. Reproductive activity of females also was not significant. However, risk for bone sarcoma was significantly influenced by age at gonadectomy in both males and females (1-in-4 lifetime risk for osteosarcoma with gonadectomy before age 1). Practical clinical trials can now be designed to test delay and prevention strategies, possibly also leading to novel strategies for decreasing osteosarcoma-related mortality in humans.

COMMENTARY: This study showed that exposure to endogenous sex hormones appears to be protective against bone sarcoma, as male and female dogs that underwent gonadectomy before age 1 had approximately a 1-in-4 lifetime risk for bone sarcoma, significantly more than sexually intact dogs. This extremely interesting work could lead to further studies that might have a profound impact on how we look at spaying and neutering. - R. Michael Thomas, DVM

Endogenous gonadal hormone exposure and bone sarcoma risk. Cooley DM, Baranak BC, Schlittler DL, et al. CANCER EPIDEMIOL BIOMARKERS PREV 11:1434-1440,
2004.

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Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL injury.
Clin Orthop [429]:301-5 2004 Dec

Slauterbeck JR, Pankratz K, Xu KT, Bozeman SC, Hardy DM
Texas Tech University Health Sciences Center, Department of Orthopaedic Surgery, 3601 4th St., 4A136, Lubbock, TX 79430, USA. jimmy.slauterbeck@ttuhsc.edu
To determine whether canine ovariohysterectomy or orchiectomy affects the prevalence of anterior cruciate ligament injury, we compared injury rates of anterior cruciate ligaments of animals that had gonadectomy and animals that were sexually intact as a function of gender, breed, or size. Records of 3218 dogs treated in one orthopaedic veterinary practice during a 2-year period were retrospectively reviewed. Anterior cruciate ligament injury, diagnosed by a history of acute hind limb lameness and by positive anterior drawer test, was confirmed at the time of surgery. The prevalence of anterior cruciate ligament rupture in all dogs was 3.48%. Females that had ovariohysterectomy and males that had orchiectomy had a significantly higher prevalence of anterior cruciate ligament rupture than the sexually intact dogs. Larger dogs had an increased prevalence of anterior cruciate ligament injury compared with smaller or medium-sized dogs, with the increased rupture rates for sterilized animals holding across breeds and sizes. Sterilization of either gender increased the prevalence of anterior cruciate ligament injury, suggesting a potential effect of gonadal gender on prevalence of injury of this ligament.

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Health
Keeping Ovaries After Hysterectomy Boosts Survival
By Kathleen Doheny
HealthDay Reporter


MONDAY, Aug. 1 (HealthDay News) -- Removing the ovaries along with the uterus during a hysterectomy done for noncancerous conditions is common in women over the age of 45, but a new study suggests it may not be the wisest course for long-term survival.

Keeping the ovaries is clearly best for women up to age 65 who are at average risk of getting ovarian cancer and get a hysterectomy for noncancerous conditions, said study author Dr. William Parker, a staff gynecologist at Santa Monica-UCLA Medical Center in Los Angeles. His finding appears in the August issue of Obstetrics & Gynecology.

In his review of 20 years of published data from various sources, Parker and his team found that preserving the ovaries in this group of women reduces their risk for heart disease and hip fractures.

"Twenty-five times more women die from heart disease every year than from ovarian cancer," Parker said.

For many years, the prevailing medical wisdom has been to remove the ovaries when the uterus is removed if women are past childbearing age to prevent ovarian cancer, Parker said. About half of women have their ovaries removed during hysterectomy.

However, the ovaries keep making small amounts of estrogen for years after natural menopause. Ovarian testosterone and androstenedione, two hormones, have been documented in some women in their 80s. Muscle and fat cells turn testosterone into circulating estrogen, in turn protecting against heart disease and osteoporosis.

Each year in the United States, more than 600,000 hysterectomies are performed. Ninety percent are performed for benign diseases, Parker said, such as uterine fibroids or endometriosis, in which the lining of the uterus begins to grow on the outside of the uterus and on nearby organs.

Parker's team tried to find out the age-specific risks for five conditions linked to the presence or absence of ovaries, including ovarian cancer, breast cancer, heart disease, hip fractures and stroke. They compared four strategies for hypothetical groups of women aged 40 to 80 who had a hysterectomy: ovary conservation with or without estrogen therapy later, and ovary removal with or without estrogen therapy later.

For women at average risk of ovarian cancer, heart disease, osteoporosis, breast cancer and stroke, the probability of survival to age 80 after hysterectomy at ages 50 to 54 ranged from 62 percent for those who kept their ovaries but didn't take estrogen, to 53 percent for those who had their ovaries removed but didn't take estrogen.

Keeping the ovaries without estrogen therapy reduced the percent of women dying by age 80 of heart disease from 15 percent to 7 percent, and those dying of hip fractures from nearly 5 percent to 3 percent.

The reductions in those two diseases, Parker said, far outweigh the increase in ovarian cancer deaths by age 80.

"If you take out the ovaries, the risk of ovarian cancer goes to zero," Parker said, "but you lose the protection against heart disease and the prevention of osteoporosis."

Was he surprised? "Yes. I really did think that taking out the ovaries wasn't beneficial for [overall] mortality," Parker said. "But I didn't suspect that leaving them in would be so clearly beneficial."

Another expert familiar with the new study, Dr. Richard Paulson, a professor of reproductive medicine at the University of Southern California, Los Angeles, praised the work. "It's wonderful," he said. "When I first read it, my first thought was, why has this not been done before?"

"What has been lacking up to this point was a good analysis for the data. You've got the cancer doctors saying, 'You can't leave them behind, the patient is going to get cancer [of the ovaries] and die.' On the other hand, you have the hormone doctors, the endocrinologists who are saying that the postmenopausal ovaries make important hormones, and we should leave them intact. What was needed was for someone to crunch the numbers and come up with relative risks."

Neither Paulson nor Parker think practice will change overnight. But the new study is food for thought, and women aged 45 and above who are facing a hysterectomy for noncancerous conditions should be aware of the new analysis, they said.

More information

To learn more about hysterectomy, visit the The National Women's Health Information Center.

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Spontaneous hormonal variations in male cats following gonadectomy
J Feline Med Surg. May 2006;0(0):.
Lucile J M Martin, Brigitte Siliart, Henri J W Dumon, Patrick Nguyen
Ecole Nationale Veterinaire de Nantes, Unite de Nutrition et Endocrinologie, Route de Gachet – BP 40706, 44307 Nantes Cedex 3, France.

Abstract
The increased prevalence of obesity after neutering in cats is problematic in veterinary practice. Although many factors seem to be involved, the role of prolactin (PRL) and insulin-like growth factor-I (IGF-I), both implicated in adipose tissue development and glucose intolerance, should be considered. Seven male cats were castrated when 11 months old. Body weight was then recorded for 56 weeks and PRL, IGF-I and leptin assayed for 44 weeks. Body weight increased steadily but only significantly after 36 weeks. It stabilised after 44 weeks, and the cats then gained about 20% of their initial body weight. IGF-I increased rapidly and was significantly higher by week 3. PRL and leptin increased with initial peaks during the eighth and eleventh weeks, respectively. This study confirms that castration rapidly modifies the hormonal balance, partly explaining the body weight increase, and that hormonal changes precede this body weight increase. Hyperleptinaemia is apparently a consequence of excess weight.

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Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs
Laura J. Sanborn, M.S.
May 14, 2007
Precis
At some point, most of us with an interest in dogs will have to consider whether or not to spay / neuter our
pet. Tradition holds that the benefits of doing so at an early age outweigh the risks. Often, tradition holds
sway in the decision-making process even after countervailing evidence has accumulated.
Ms Sanborn has reviewed the veterinary medical literature in an exhaustive and scholarly treatise,
attempting to unravel the complexities of the subject. More than 50 peer-reviewed papers were examined to
assess the health impacts of spay / neuter in female and male dogs, respectively. One cannot ignore the
findings of increased risk from osteosarcoma, hemangiosarcoma, hypothyroidism, and other less frequently
occurring diseases associated with neutering male dogs. It would be irresponsible of the veterinary
profession and the pet owning community to fail to weigh the relative costs and benefits of neutering on the
animal’s health and well-being. The decision for females may be more complex, further emphasizing the
need for individualized veterinary medical decisions, not standard operating procedures for all patients.
No sweeping generalizations are implied in this review. Rather, the author asks us to consider all the health
and disease information available as individual animals are evaluated. Then, the best decisions should be
made accounting for gender, age, breed, and even the specific conditions under which the long-term care,
housing and training of the animal will occur.
This important review will help veterinary medical care providers as well as pet owners make informed
decisions. Who could ask for more?
Larry S. Katz, PhD
Associate Professor and Chair
Animal Sciences
Rutgers University
New Brunswick, NJ 08901
INTRODUCTION
Dog owners in America are frequently advised to spay/neuter their dogs for health reasons. A number of
health benefits are cited, yet evidence is usually not cited to support the alleged health benefits.
When discussing the health impacts of spay/neuter, health risks are often not mentioned. At times, some
risks are mentioned, but the most severe risks usually are not.
This article is an attempt to summarize the long-term health risks and benefits associated with spay/neuter
in dogs that can be found in the veterinary medical literature. This article will not discuss the impact of
spay/neuter on population control, or the impact of spay/neuter on behavior.
Nearly all of the health risks and benefits summarized in this article are findings from retrospective
epidemiological research studies of dogs, which examine potential associations by looking backwards in
time. A few are from prospective research studies, which examine potential associations by looking forward
in time.
SUMMARY
An objective reading of the veterinary medical literature reveals a complex situation with respect to the longterm
health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter
Page 2 of 12
correlates with both positive AND adverse health effects in dogs. It also suggests how much we really do
not yet understand about this subject.
On balance, it appears that no compelling case can be made for neutering most male dogs, especially
immature male dogs, in order to prevent future health problems. The number of health problems associated
with neutering may exceed the associated health benefits in most cases.
On the positive side, neutering male dogs
• eliminates the small risk (probably <1%) of dying from testicular cancer
• reduces the risk of non-cancerous prostate disorders
• reduces the risk of perianal fistulas
• may possibly reduce the risk of diabetes (data inconclusive)
On the negative side, neutering male dogs
• if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a
common cancer in medium/large and larger breeds with a poor prognosis.
• increases the risk of cardiac hemangiosarcoma by a factor of 1.6
• triples the risk of hypothyroidism
• increases the risk of progressive geriatric cognitive impairment
• triples the risk of obesity, a common health problem in dogs with many associated health problems
• quadruples the small risk (<0.6%) of prostate cancer
• doubles the small risk (<1%) of urinary tract cancers
• increases the risk of orthopedic disorders
• increases the risk of adverse reactions to vaccinations
For female dogs, the situation is more complex. The number of health benefits associated with spaying may
exceed the associated health problems in some (not all) cases. On balance, whether spaying improves the
odds of overall good health or degrades them probably depends on the age of the female dog and the
relative risk of various diseases in the different breeds.
On the positive side, spaying female dogs
• if done before 2.5 years of age, greatly reduces the risk of mammary tumors, the most common
malignant tumors in female dogs
• nearly eliminates the risk of pyometra, which otherwise would affect about 23% of intact female
dogs; pyometra kills about 1% of intact female dogs
• reduces the risk of perianal fistulas
• removes the very small risk (
0.5%) from uterine, cervical, and ovarian tumors
On the negative side, spaying female dogs
• if done before 1 year of age, significantly increases the risk of osteosarcoma (bone cancer); this is a
common cancer in larger breeds with a poor prognosis
• increases the risk of splenic hemangiosarcoma by a factor of 2.2 and cardiac hemangiosarcoma by
a factor of >5; this is a common cancer and major cause of death in some breeds
• triples the risk of hypothyroidism
• increases the risk of obesity by a factor of 1.6-2, a common health problem in dogs with many
associated health problems
• causes urinary “spay incontinence” in 4-20% of female dogs
• increases the risk of persistent or recurring urinary tract infections by a factor of 3-4
• increases the risk of recessed vulva, vaginal dermatitis, and vaginitis, especially for female dogs
spayed before puberty
• doubles the small risk (<1%) of urinary tract tumors
• increases the risk of orthopedic disorders
• increases the risk of adverse reactions to vaccinations
One thing is clear – much of the spay/neuter information that is available to the public is unbalanced and
contains claims that are exaggerated or unsupported by evidence. Rather than helping to educate pet
Page 3 of 12
owners, much of it has contributed to common misunderstandings about the health risks and benefits
associated of spay/neuter in dogs.
The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear
to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically
mature, or perhaps in the case of many male dogs, foregoing it altogether unless medically necessary.
The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Breed,
age, and gender are variables that must be taken into consideration in conjunction with non-medical factors
for each individual dog. Across-the-board recommendations for all pet dogs do not appear to be
supportable from findings in the veterinary medical literature.
FINDINGS FROM STUDIES
This section summarizes the diseases or conditions that have been studied with respect to spay/neuter in
dogs.
Complications from Spay/Neuter Surgery
All surgery incurs some risk of complications, including adverse reactions to anesthesia, hemorrhage,
inflammation, infection, etc. Complications include only immediate and near term impacts that are clearly
linked to the surgery, not to longer term impacts that can only be assessed by research studies.
At one veterinary teaching hospital where complications were tracked, the rates of intraoperative,
postoperative and total complications were 6.3%, 14.1% and 20.6%, respectively as a result of spaying
female dogs1. Other studies found a rate of total complications from spaying of 17.7%2 and 23%3. A study
of Canadian veterinary private practitioners found complication rates of 22% and 19% for spaying female
dogs and neutering male dogs, respectively4.
Serious complications such as infections, abscesses, rupture of the surgical wound, and chewed out sutures
were reported at a 1- 4% frequency, with spay and castration surgeries accounting for 90% and 10% of
these complications, respectively.4
The death rate due to complications from spay/neuter is low, at around 0.1%2.
Prostate Cancer
Much of the spay/neuter information available to the public asserts that neutering will reduce or eliminate the
risk that male dogs develop prostate cancer. This would not be an unreasonable assumption, given that
prostate cancer in humans is linked to testosterone. But the evidence in dogs does not support this claim.
In fact, the strongest evidence suggests just the opposite.
There have been several conflicting epidemiological studies over the years that found either an increased
risk or a decreased risk of prostate cancer in neutered dogs. These studies did not utilize control
populations, rendering these results at best difficult to interpret. This may partially explain the conflicting
results.
More recently, two retrospective studies were conducted that did utilize control populations. One of these
studies involved a dog population in Europe5 and the other involved a dog population in America6. Both
studies found that neutered male dogs have a four times higher risk of prostate cancer than intact dogs.
Based on their results, the researchers suggest a cause-and-effect relationship: “this suggests that
castration does not initiate the development of prostatic carcinoma in the dog, but does favor tumor
progression”5 and also “Our study found that most canine prostate cancers are of ductal/urothelial
origin….The relatively low incidence of prostate cancer in intact dogs may suggest that testicular hormones
Page 4 of 12
are in fact protective against ductal/urothelial prostatic carcinoma, or may have indirect effects on cancer
development by changing the environment in the prostate.”6
This needs to be put in perspective. Unlike the situation in humans, prostate cancer is uncommon in dogs.
Given an incidence of prostate cancer in dogs of less than 0.6% from necropsy studies7, it is difficult to see
that the risk of prostate cancer should factor heavily into most neutering decisions. There is evidence for an
increased risk of prostate cancer in at least one breed (Bouviers)5, though very little data so far to guide us
in regards to other breeds.
Testicular Cancer
Since the testicles are removed with neutering, castration removes any risk of testicular cancer (assuming
the castration is done before cancer develops). This needs to be compared to the risk of testicular cancer in
intact dogs.
Testicular tumors are not uncommon in older intact dogs, with a reported incidence of 7%8. However, the
prognosis for treating testicular tumors is very good owing to a low rate of metastasis9, so testicular cancer
is an uncommon cause of death in intact dogs. For example, in a Purdue University breed health survey of
Golden Retrievers10, deaths due to testicular cancer were sufficiently infrequent that they did not appear on
list of significant causes of "Years of Potential Life Lost for Veterinary Confirmed Cause of Death” even
though 40% of GR males were intact. Furthermore, the GRs who were treated for testicular tumors had a
90.9% cure rate. This agrees well with other work that found 6-14% rates of metastasis for testicular tumors
in dogs11.
The high cure rate of testicular tumors combined with their frequency suggests that fewer than 1% of intact
male dogs will die of testicular cancer.
In summary, though it may be the most common reason why many advocate neutering young male dogs,
the risk from life threatening testicular cancer is sufficiently low that neutering most male dogs to prevent it is
difficult to justify.
An exception might be bilateral or unilateral cryptorchids, as testicles that are retained in the abdomen are
13.6 times more likely to develop tumors than descended testicles12 and it is also more difficult to detect
tumors in undescended testicles by routine physical examination.
Osteosarcoma (Bone Cancer)
A multi-breed case-control study of the risk factors for osteosarcoma found that spay/neutered dogs (males
or females) had twice the risk of developing osteosarcoma as did intact dogs13.
This risk was further studied in Rottweilers, a breed with a relatively high risk of osteosarcoma. This
retrospective cohort study broke the risk down by age at spay/neuter, and found that the elevated risk of
osteosarcoma is associated with spay/neuter of young dogs14. Rottweilers spayed/neutered before one
year of age were 3.8 (males) or 3.1 (females) times more likely to develop osteosarcoma than intact dogs.
Indeed, the combination of breed risk and early spay/neuter meant that Rottweilers spayed/neutered before
one year of age had a 28.4% (males) and 25.1% (females) risk of developing osteosarcoma. These results
are consistent with the earlier multi-breed study13 but have an advantage of assessing risk as a function of
age at neuter. A logical conclusion derived from combining the findings of these two studies is that
spay/neuter of dogs before 1 year of age is associated with a significantly increased risk of osteosarcoma.
The researchers suggest a cause-and-effect relationship, as sex hormones are known to influence the
maintenance of skeletal structure and mass, and also because their findings showed an inverse relationship
between time of exposure to sex hormones and risk of osteosarcoma.14
Page 5 of 12
The risk of osteosarcoma increases with increasing breed size and especially height13. It is a common
cause of death in medium/large, large, and giant breeds. Osteosarcoma is the third most common cause of
death in Golden Retrievers10 and is even more common in larger breeds13.
Given the poor prognosis of osteosarcoma and its frequency in many breeds, spay/neuter of immature dogs
in the medium/large, large, and giant breeds is apparently associated with a significant and elevated risk of
death due to osteosarcoma.
Mammary Cancer (Breast Cancer)
Mammary tumors are by far the most common tumors in intact female dogs, constituting some 53% of all
malignant tumors in female dogs in a study of dogs in Norway15 where spaying is much less common than in
the USA.
50-60% of mammary tumors are malignant, for which there is a significant risk of metastasis16. Mammary
tumors in dogs have been found to have estrogen receptors17, and the published research18 shows that the
relative risk (odds ratio) that a female will develop mammary cancer compared to the risk in intact females is
dependent on how many estrus cycles she experiences:
# of estrus cycles before spay Odds Ratio
None 0.005
1 0.08
2 or more 0.26
Intact 1.00
The same data when categorized differently showed that the relative risk (odds ratio) that females will
develop mammary cancer compared to the risk in intact females indicated that:
Age at Spaying Odds Ratio

29 months 0.06
 30 months 0.40 (not statistically significant at the P<0.05 level)
Intact 1.00
Please note that these are RELATIVE risks. This study has been referenced elsewhere many times but the
results have often been misrepresented as absolute risks.
A similar reduction in breast cancer risk was found for women under the age of 40 who lost their estrogen
production due to “artificial menopause”19 and breast cancer in humans is known to be estrogen activated.
Mammary cancer was found to be the 10th most common cause of years of lost life in Golden Retrievers,
even though 86% of female GRs were spayed, at a median age of 3.4 yrs10. Considering that the female
subset accounts for almost all mammary cancer cases, it probably would rank at about the 5th most common
cause of years of lost life in female GRs. It would rank higher still if more female GRs had been kept intact
up to 30 months of age.
Boxers, cocker spaniels, English Springer spaniels, and dachshunds are breeds at high risk of mammary
tumors15. A population of mostly intact female Boxers was found to have a 40% chance of developing
mammary cancer between the ages of 6-12 years of age15. There are some indications that purebred dogs
may be at higher risk than mixed breed dogs, and purebred dogs with high inbreeding coefficients may be at
higher risk than those with low inbreeding coefficients20. More investigation is required to determine if these
are significant.
In summary, spaying female dogs significantly reduces the risk of mammary cancer (a common cancer),
and the fewer estrus cycles experienced at least up to 30 months of age, the lower the risk will be.
Page 6 of 12
Female Reproductive Tract Cancer (Uterine, Cervical, and Ovarian Cancers)
Uterine/cervical tumors are rare in dogs, constituting just 0.3% of tumors in dogs21.
Spaying will remove the risk of ovarian tumors, but the risk is only 0.5%22.
While spaying will remove the risk of reproductive tract tumors, it is unlikely that surgery can be justified to
prevent the risks of uterine, cervical, and ovarian cancers as the risks are so low.
Urinary Tract Cancer (Bladder and Urethra Cancers)
An age-matched retrospective study found that spay/neuter dogs were two times more likely to develop
lower urinary tract tumors (bladder or urethra) compared to intact dogs23. These tumors are nearly always
malignant, but are infrequent, accounting for less than 1% of canine tumors. So this risk is unlikely to weigh
heavily on spay/neuter decisions.
Airedales, Beagles, and Scottish Terriers are at elevated risk for urinary tract cancer while German
Shepherds have a lower than average risk23.
Hemangiosarcoma
Hemangiosarcoma is a common cancer in dogs. It is a major cause of death in some breeds, such as
Salukis, French Bulldogs, Irish Water Spaniels, Flat Coated Retrievers, Golden Retrievers, Boxers, Afghan
Hounds, English Setters, Scottish Terriesr, Boston Terriers, Bulldogs, and German Shepherd Dogs24.
In an aged-matched case controlled study, spayed females were found to have a 2.2 times higher risk of
splenic hemangiosarcoma compared to intact females24.
A retrospective study of cardiac hemangiosarcoma risk factors found a >5 times greater risk in spayed
female dogs compared to intact female dogs and a 1.6 times higher risk in neutered male dogs compared to
intact male dogs.25 The authors suggest a protective effect of sex hormones against hemangiosarcoma,
especially in females.
In breeds where hermangiosarcoma is an important cause of death, the increased risk associated with
spay/neuter is likely one that should factor into decisions on whether or when to sterilize a dog.
Hypothyroidism
Spay/neuter in dogs was found to be correlated with a three fold increased risk of hypothyroidism compared
to intact dogs. 26.
The researchers suggest a cause-and-effect relationship: They wrote: “More important [than the mild direct
impact on thyroid function] in the association between [spaying and] neutering and hypothyroidism may be
the effect of sex hormones on the immune system. Castration increases the severity of autoimmune
thyroiditis in mice” which may explain the link between spay/neuter and hypothyroidism in dogs.
Hypothyroidism in dogs causes obesity, lethargy, hair loss, and reproductive abnormalities.27
The lifetime risk of hypothyroidism in breed health surveys was found to be 1 in 4 in Golden Retrievers10, 1
in 3 in Akitas28, and 1 in 13 in Great Danes29.
Page 7 of 12
Obesity
Owing to changes in metabolism, spay/neuter dogs are more likely to be overweight or obese than intact
dogs. One study found a two fold increased risk of obesity in spayed females compared to intact females30.
Another study found that spay/neuter dogs were 1.6 (females) or 3.0 (males) times more likely to be obese
than intact dogs, and 1.2 (females) or 1.5 (males) times more likely to be overweight than intact dogs31.
A survey study of veterinary practices in the UK found that 21% of dogs were obese.30
Being obese and/or overweight is associated with a host of health problems in dogs. Overweight dogs are
more likely to be diagnosed with hyperadrenocorticism, ruptured cruciate ligament, hypothyroidism, lower
urinary tract disease, and oral disease32. Obese dogs are more likely to be diagnosed with hypothyroidism,
diabetes mellitus, pancreatitis, ruptured cruciate ligament, and neoplasia (tumors)32.
Diabetes
Some data indicate that neutering doubles the risk of diabetes in male dogs, but other data showed no
significant change in diabetes risk with neutering33. In the same studies, no association was found between
spaying and the risk of diabetes.
Adverse Vaccine Reactions
A retrospective cohort study of adverse vaccine reactions in dogs was conducted, which included allergic
reactions, hives, anaphylaxis, cardiac arrest, cardiovascular shock, and sudden death. Adverse reactions
were 30% more likely in spayed females than intact females, and 27% more likely in neutered males than
intact males34.
The investigators discuss possible cause-and-effect mechanisms for this finding, including the roles that sex
hormones play in body’s ability to mount an immune response to vaccination.34
Toy breeds and smaller breeds are at elevated risk of adverse vaccine reactions, as are Boxers, English
Bulldogs, Lhasa Apsos, Weimaraners, American Eskimo Dogs, Golden Retrievers, Basset Hounds, Welsh
Corgis, Siberian Huskies, Great Danes, Labrador Retrievers, Doberman Pinschers, American Pit Bull
Terriers, and Akitas.34 Mixed breed dogs were found to be at lower risk, and the authors suggest genetic
hetereogeneity (hybrid vigor) as the cause.
Urogenital Disorders
Urinary incontinence is common in spayed female dogs, which can occur soon after spay surgery or after a
delay of up to several years. The incidence rate in various studies is 4-20% 35,36,37 for spayed females
compared to only 0.3% in intact females38. Urinary incontinence is so strongly linked to spaying that it is
commonly called “spay incontinence” and is caused by urethral sphincter incompetence39, though the
biological mechanism is unknown. Most (but not all) cases of urinary incontinence respond to medical
treatment, and in many cases this treatment needs to be continued for the duration of the dog’s life.40
A retrospective study found that persistent or recurring urinary tract (bladder) infections (UTIs) were 3-4
times more likely in spayed females dogs than in intact females41. Another retrospective study found that
female dogs spayed before 5 ½ months of age were 2.76 times more likely to develop UTIs compared to
those spayed after 5 ½ months of age.42
Depending on the age of surgery, spaying causes abnormal development of the external genitalia. Spayed
females were found to have an increased risk of recessed vulva, vaginal dermatitis, vaginitis, and UTIs.43
The risk is higher still for female dogs spayed before puberty.43
Page 8 of 12
Pyometra (Infection of the Uterus)
Pet insurance data in Sweden (where spaying is very uncommon) found that 23% of all female dogs
developed pyometra before 10 years of age44. Bernese Mountain dogs, Rottweilers, rough-haired Collies,
Cavalier King Charles Spaniels and Golden Retrievers were found to be high risk breeds44. Female dogs
that have not whelped puppies are at elevated risk for pyometra45. Rarely, spayed female dogs can
develop “stump pyometra” related to incomplete removal of the uterus.
Pyometra can usually be treated surgically or medically, but 4% of pyometra cases led to death44.
Combined with the incidence of pyometra, this suggests that about 1% of intact female dogs will die from
pyometra.
Perianal Fistulas
Male dogs are twice as likely to develop perianal fistulas as females, and spay/neutered dogs have a
decreased risk compared to intact dogs46.
German Shepherd Dogs and Irish Setters are more likely to develop perianal fistulas than are other
breeds.46
Non-cancerous Disorders of the Prostate Gland
The incidence of benign prostatic hypertrophy (BPH, enlarged prostate) increases with age in intact male
dogs, and occurs in more than 80% of intact male dogs older than the age of 5 years47. Most cases of BPH
cause no problems, but in some cases the dog will have difficulty defecating or urinating.
Neutering will prevent BPH. If neutering is done after the prostate has become enlarged, the enlarged
prostate will shrink relatively quickly.
BPH is linked to other problems of the prostate gland, including infections, abscesses, and cysts, which can
sometimes have serious consequences.
Orthopedic Disorders
In a study of beagles, surgical removal of the ovaries (as happens in spaying) caused an increase in the rate
of remodeling of the ilium (pelvic bone)48, suggesting an increased risk of hip dysplasia with spaying.
Spaying was also found to cause a net loss of bone mass in the spine 49.
Spay/neuter of immature dogs delays the closure of the growth plates in bones that are still growing,
causing those bones to end up significantly longer than in intact dogs or those spay/neutered after
maturity50. Since the growth plates in various bones close at different times, spay/neuter that is done after
some growth plates have closed but before other growth plates have closed might result in a dog with
unnatural proportions, possibly impacting performance and long term durability of the joints.
Spay/neuter is associated with a two fold increased risk of cranial cruciate ligament rupture51. Perhaps this
is associated with the increased risk of obesity30.
Spay/neuter before 5 ½ months of age is associated with a 70% increased aged-adjusted risk of hip
dysplasia compared to dogs spayed/neutered after 5 ½ months of age, though there were some indications
that the former may have had a lower severity manifestation of the disease42. The researchers suggest “it
is possible that the increase in bone length that results from early-age gonadectomy results in changes in
joint conformation, which could lead to a diagnosis of hip dysplasia.”
Page 9 of 12
In a breed health survey study of Airedales, spay/neuter dogs were significantly more likely to suffer hip
dysplasia as well as “any musculoskeletal disorder”, compared to intact dogs52, however possible
confounding factors were not controlled for, such as the possibility that some dogs might have been
spayed/neutered because they had hip dysplasia or other musculoskeletal disorders.
Compared to intact dogs, another study found that dogs neutered six months prior to a diagnosis of hip
dysplasia were 1.5 times as likely to develop clinical hip dysplasia.53
Compared to intact dogs, spayed/neutered dogs were found to have a 3.1 fold higher risk of patellar
luxation.54
Geriatric Cognitive Impairment
Neutered male dogs and spayed female dogs are at increased risk of progressing from mild to severe
geriatric cognitive impairment compared to intact male dogs55. There weren’t enough intact geriatric
females available for the study to determine their risk.
Geriatric cognitive impairment includes disorientation in the house or outdoors, changes in social
interactions with human family members, loss of house training, and changes in the sleep-wake cycle55.
The investigators state “This finding is in line with current research on the neuro-protective roles of
testosterone and estrogen at the cellular level and the role of estrogen in preventing Alzheimer’s disease in
human females. One would predict that estrogens would have a similar protective role in the sexually intact
female dogs; unfortunately too few sexually intact female dogs were available for inclusion in the present
study to test the hypothesis”55
CONCLUSIONS
An objective reading of the veterinary medical literature reveals a complex situation with respect to the longterm
health risks and benefits associated with spay/neuter in dogs. The evidence shows that spay/neuter
correlates with both positive AND adverse health effects in dogs. It also suggests how much we really do
not yet understand about this subject.
On balance, it appears that no compelling case can be made for neutering most male dogs to prevent future
health problems, especially immature male dogs. The number of health problems associated with neutering
may exceed the associated health benefits in most cases.
For female dogs, the situation is more complex. The number of health benefits associated with spaying may
exceed the associated health problems in many (not all) cases. On balance, whether spaying improves the
odds of overall good health or degrades them probably depends on the age of the dog and the relative risk
of various diseases in the different breeds.
The traditional spay/neuter age of six months as well as the modern practice of pediatric spay/neuter appear
to predispose dogs to health risks that could otherwise be avoided by waiting until the dog is physically
mature, or perhaps in the case of many male dogs, foregoing it altogether unless medically necessary.
The balance of long-term health risks and benefits of spay/neuter will vary from one dog to the next. Breed,
age, and gender are variables that must be taken into consideration in conjunction with non-medical factors
for each individual dog. Across-the-board recommendations for all dogs do not appear to be supportable
from findings in the veterinary medical literature.
Page 10 of 12
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