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The Question Of Neutering and at what age
(Put together by Gregg Tonkin, Little River Labradors from postings by Pam Davol PHD and Chris Zink DVM, PhD, DACVP)
Owners who are considering neutering need to take all factors into consideration, not simply the benefits of neutering when making a decision as to
when to neuter.
If one looks close enough, one will find that neutering is one of those topics in veterinary medicine that is extremely biased: that is, most often one
will find more emphasis placed on the pros of neutering with more often than not, very little or no discussion of the cons. Veterinarians, and
responsible breeders as well, face a true dilemma when discussing neutering. The overpopulation crisis presents a very real concern with regard to
the necessity of ownership responsibility. Prepubertal/early neutering or required neutering provides a means for vets/breeders to enforce owner
responsibility by ensuring surgical sterilization of dogs not destined to be used in breeding programs. Again, this enforced neutering is typically
presented along with a preamble of all the benefits that go along with neutering. However, I believe that breeders, if not veterinarians, need to begin
questioning the ethics of this approach to prompt or require owners to neuter; especially in light of the facts that early neutering may not be as
benign a process to the health of a dog as one would believe.
Yes, neutering prior to the beginning of estrus does reduce risk for mammary cancer in females, but it also significantly increases risk for urinary
incontinence in bitches which predisposes these bitches to diethylstilbestrol (DES) dependency (Stocklin-Gautschi et al., J. Reprod. Fertile. Suppl.
57:233-6, 2001 and many other references)--in some instances, DES is not effective at controlling incontinence and will force some owners to
elect euthanasia. Though with lesser risk compared to females, early neutering also increases risk of urethral sphincter incontinence in males (A.
Aaron et al., Vet Rec. 139:542-6, 1996.)
With regard to cancer, spayed females have a 4 times greater risk for developing cardiac hemangiosarcomas (vascular tumors) compared to intact
females (neutered males also show a significant increase in risk for these tumors compared to intact males) (Ware and Hysper, J. Vet. Intern. Med.
13:95-103, 1999.). Additionally, both neutered males and females have a 2-fold greater risk for developing bone tumors (osteosarcoma)
compared to intact males and females (Ru et al., Vet J. 156:31-9, 1998.).
Some evidence suggests that early neutering may also predispose to endocrine disorders later in life (Panciera DL. J. Am. Vet. Med. Assoc.,
204:761-7 1994.). Furthermore, there is also an indication that early neutering (because absence of sex hormones delays maturation of osteoclasts
and thus results in delayed closing of the growth plates in the long-bones) may predispose to increased risk for various orthopedic disorders (such
as cruciate ligament disease as I had mentioned in a previous post). Also, some evidence suggests that there is a correlation between increased
time for growth plate closure and incidence of HD in Labs (Todhunter et al. J. Am. Vet Assoc., 1997).
If one conducted a research of the literature on the detrimental effects on physiological development associated with sex hormone deficiencies
during adolescent development in any other species other than the dog and cat, one will find a wealth of literature stressing the importance of sex
hormones for sound physiological, endocrine and metabolic development. Additionally, if one examines the scientific research that reports the
benefits of early neutering in absence of any side-effects in dogs, one will discover that the methodology of these studies are designed in very
specific ways to assure that outcome in neutering is presented in a favorable light (this does not mean that the data is biased, this simply means that
the comparisons made do not provide for adequate interpretation of long-term effects of neutering).
In light of this, though it is understandable for vets/breeders to urge dog owners to neuter their pets early with regard to the greater good (i.e.
reducing risk of accidental breeding), the physiological soundness of the individual dog should take precedence over any other issues. As such, it is
my opinion, based upon the literature that I have reviewed that to reduce risks to physiological soundness, etc, that I am of the personal opinion
that dogs should be a minimum of 1 year of age before neutering.
To Neuter or not to Neuter...
(written by Pam Davol of Wing-In-Wave Labradors, a noted research scientist and a Labrador genetic expert)
"And in Addition"
There are a number of studies that suggest that those of us with canine athletes should be carefully considering our current recommendations to
spay or neuter all dogs at 6 months of age or earlier. A study by Salmeri et al in 1991 (Salmeri et al JAVMA 1991;198:1193-1203) found that
bitches spayed at 7 weeks were significantly taller than those spayed at 7 months, and that those spayed at at 7 months had significantly delayed
closure of the growth plates than those not spayed (or presumably spayed after the growth plates had closed). The sex hormones close the growth
plates, so the bones of dogs or bitches neutered or spayed before puberty continue to grow. This growth frequently results in a dog that does not
have the same body proportions as he/she was genetically meant to. For example, if the femur is normal length at 8 months when a dog gets
spayed or neutered, but the tibia, which normally stops growing at 12 to 14 months of age continues to grow, then an abnormal angle may develop
at the stifle. In addition, with the extra growth, the lower leg below the stifle becomes heavier (because it is longer), causing increased stresses on
the cranial cruciate ligament. This is confirmed by a recent study showing that spayed and neutered dogs have a higher incidence of CCL rupture
(Slauterbeck JR, Pankratz K, Xu KT, Bozeman SC, Hardy DM. Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL
injury. Clin Orthop Relat Res. 2004 Dec;(429):301-5).
In addition, a study in 2004 in JAVMA (Spain et al. JAVMA 2004;224:380-387) showed that dogs spayed or neutered before 5 1/2 months had
a significantly higher incidence of hip dysplasia than dogs spayed or neutered after 5 1/2 months of age. If I were a breeder, I would be very
concerned about this, because it would mean that I might be making incorrect breeding decisions if I were considering the hip status of pups I sold
that were spayed or neutered early. Interestingly, this same author also identified an increased incidence of sexual behaviors in males and females
that were neutered early.
A number of studies, including the one by Spain referenced above, have shown that there is an increase in the incidence of female urinary
incontinence in dogs spayed early. This problem is an inconvenience, and not usually life-threatening, but nonetheless one that requires the dog to
be medicated for life.
Yes, there is the concern that there is an increased risk of mammary cancer if a dog has a heat cycle. But it is my observation that fewer canine
athletes develop mammary cancer as compared to the number that damage their cranial cruciate ligaments. In addition, only about 50 % of
mammary cancers are malignant, and those that are malignant don't metastasize very often, particularly in these days when there is early
identification and removal of lumps found on our dogs.
In addition, when considering cancer, there is another study of 3218 dogs that showed that dogs that were neutered before a year of age had a
significantly increased chance of developing bone cancer (Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters D,
Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1434-40), a cancer that is much more life-threatening than mammary cancer, and which
affects both genders.
Finally, in another study, unneutered males were significantly less likely than neutered males to suffer cognitive impairment when they were older
(Hart BL. J Am Vet Med Assoc. 2001 Jul 1;219(1):51-6). Females were not evaluated in that study.
For these reasons, I have significant concerns with spaying or neutering dogs before puberty, particularly for the canine athlete. And frankly, if
something is more healthy for the canine athlete, would we not also want that for pet dogs as well? I think it is important, therefore, that we assess
each situation individually. If a pet dog is going to live with an intelligent, well-informed family that understands the problem of pet overpopulation
and can be trusted to keep their dogs under their control at all times and to not breed them, I do not recommend spaying or neutering before 14
months of age.
(written by Chris Zink DVM, PhD, DACVP, noted author and consultant on canine sports medicine) see Early Spay-Neuter Considerations for
the Canine Athlete
(Put together by Gregg Tonkin, Little River Labradors from postings by Pam Davol PHD and Chris Zink DVM, PhD, DACVP)
Owners who are considering neutering need to take all factors into consideration, not simply the benefits of neutering when making a decision as to
when to neuter.
If one looks close enough, one will find that neutering is one of those topics in veterinary medicine that is extremely biased: that is, most often one
will find more emphasis placed on the pros of neutering with more often than not, very little or no discussion of the cons. Veterinarians, and
responsible breeders as well, face a true dilemma when discussing neutering. The overpopulation crisis presents a very real concern with regard to
the necessity of ownership responsibility. Prepubertal/early neutering or required neutering provides a means for vets/breeders to enforce owner
responsibility by ensuring surgical sterilization of dogs not destined to be used in breeding programs. Again, this enforced neutering is typically
presented along with a preamble of all the benefits that go along with neutering. However, I believe that breeders, if not veterinarians, need to begin
questioning the ethics of this approach to prompt or require owners to neuter; especially in light of the facts that early neutering may not be as
benign a process to the health of a dog as one would believe.
Yes, neutering prior to the beginning of estrus does reduce risk for mammary cancer in females, but it also significantly increases risk for urinary
incontinence in bitches which predisposes these bitches to diethylstilbestrol (DES) dependency (Stocklin-Gautschi et al., J. Reprod. Fertile. Suppl.
57:233-6, 2001 and many other references)--in some instances, DES is not effective at controlling incontinence and will force some owners to
elect euthanasia. Though with lesser risk compared to females, early neutering also increases risk of urethral sphincter incontinence in males (A.
Aaron et al., Vet Rec. 139:542-6, 1996.)
With regard to cancer, spayed females have a 4 times greater risk for developing cardiac hemangiosarcomas (vascular tumors) compared to intact
females (neutered males also show a significant increase in risk for these tumors compared to intact males) (Ware and Hysper, J. Vet. Intern. Med.
13:95-103, 1999.). Additionally, both neutered males and females have a 2-fold greater risk for developing bone tumors (osteosarcoma)
compared to intact males and females (Ru et al., Vet J. 156:31-9, 1998.).
Some evidence suggests that early neutering may also predispose to endocrine disorders later in life (Panciera DL. J. Am. Vet. Med. Assoc.,
204:761-7 1994.). Furthermore, there is also an indication that early neutering (because absence of sex hormones delays maturation of osteoclasts
and thus results in delayed closing of the growth plates in the long-bones) may predispose to increased risk for various orthopedic disorders (such
as cruciate ligament disease as I had mentioned in a previous post). Also, some evidence suggests that there is a correlation between increased
time for growth plate closure and incidence of HD in Labs (Todhunter et al. J. Am. Vet Assoc., 1997).
If one conducted a research of the literature on the detrimental effects on physiological development associated with sex hormone deficiencies
during adolescent development in any other species other than the dog and cat, one will find a wealth of literature stressing the importance of sex
hormones for sound physiological, endocrine and metabolic development. Additionally, if one examines the scientific research that reports the
benefits of early neutering in absence of any side-effects in dogs, one will discover that the methodology of these studies are designed in very
specific ways to assure that outcome in neutering is presented in a favorable light (this does not mean that the data is biased, this simply means that
the comparisons made do not provide for adequate interpretation of long-term effects of neutering).
In light of this, though it is understandable for vets/breeders to urge dog owners to neuter their pets early with regard to the greater good (i.e.
reducing risk of accidental breeding), the physiological soundness of the individual dog should take precedence over any other issues. As such, it is
my opinion, based upon the literature that I have reviewed that to reduce risks to physiological soundness, etc, that I am of the personal opinion
that dogs should be a minimum of 1 year of age before neutering.
To Neuter or not to Neuter...
(written by Pam Davol of Wing-In-Wave Labradors, a noted research scientist and a Labrador genetic expert)
"And in Addition"
There are a number of studies that suggest that those of us with canine athletes should be carefully considering our current recommendations to
spay or neuter all dogs at 6 months of age or earlier. A study by Salmeri et al in 1991 (Salmeri et al JAVMA 1991;198:1193-1203) found that
bitches spayed at 7 weeks were significantly taller than those spayed at 7 months, and that those spayed at at 7 months had significantly delayed
closure of the growth plates than those not spayed (or presumably spayed after the growth plates had closed). The sex hormones close the growth
plates, so the bones of dogs or bitches neutered or spayed before puberty continue to grow. This growth frequently results in a dog that does not
have the same body proportions as he/she was genetically meant to. For example, if the femur is normal length at 8 months when a dog gets
spayed or neutered, but the tibia, which normally stops growing at 12 to 14 months of age continues to grow, then an abnormal angle may develop
at the stifle. In addition, with the extra growth, the lower leg below the stifle becomes heavier (because it is longer), causing increased stresses on
the cranial cruciate ligament. This is confirmed by a recent study showing that spayed and neutered dogs have a higher incidence of CCL rupture
(Slauterbeck JR, Pankratz K, Xu KT, Bozeman SC, Hardy DM. Canine ovariohysterectomy and orchiectomy increases the prevalence of ACL
injury. Clin Orthop Relat Res. 2004 Dec;(429):301-5).
In addition, a study in 2004 in JAVMA (Spain et al. JAVMA 2004;224:380-387) showed that dogs spayed or neutered before 5 1/2 months had
a significantly higher incidence of hip dysplasia than dogs spayed or neutered after 5 1/2 months of age. If I were a breeder, I would be very
concerned about this, because it would mean that I might be making incorrect breeding decisions if I were considering the hip status of pups I sold
that were spayed or neutered early. Interestingly, this same author also identified an increased incidence of sexual behaviors in males and females
that were neutered early.
A number of studies, including the one by Spain referenced above, have shown that there is an increase in the incidence of female urinary
incontinence in dogs spayed early. This problem is an inconvenience, and not usually life-threatening, but nonetheless one that requires the dog to
be medicated for life.
Yes, there is the concern that there is an increased risk of mammary cancer if a dog has a heat cycle. But it is my observation that fewer canine
athletes develop mammary cancer as compared to the number that damage their cranial cruciate ligaments. In addition, only about 50 % of
mammary cancers are malignant, and those that are malignant don't metastasize very often, particularly in these days when there is early
identification and removal of lumps found on our dogs.
In addition, when considering cancer, there is another study of 3218 dogs that showed that dogs that were neutered before a year of age had a
significantly increased chance of developing bone cancer (Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters D,
Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1434-40), a cancer that is much more life-threatening than mammary cancer, and which
affects both genders.
Finally, in another study, unneutered males were significantly less likely than neutered males to suffer cognitive impairment when they were older
(Hart BL. J Am Vet Med Assoc. 2001 Jul 1;219(1):51-6). Females were not evaluated in that study.
For these reasons, I have significant concerns with spaying or neutering dogs before puberty, particularly for the canine athlete. And frankly, if
something is more healthy for the canine athlete, would we not also want that for pet dogs as well? I think it is important, therefore, that we assess
each situation individually. If a pet dog is going to live with an intelligent, well-informed family that understands the problem of pet overpopulation
and can be trusted to keep their dogs under their control at all times and to not breed them, I do not recommend spaying or neutering before 14
months of age.
(written by Chris Zink DVM, PhD, DACVP, noted author and consultant on canine sports medicine) see Early Spay-Neuter Considerations for
the Canine Athlete
Early Spay-Neuter Considerations for the Canine Athlete
One Veterinarian’s Opinion
© 2005 Chris Zink DVM, PhD, DACVP
www.caninesports.com
Those of us with responsibility for the health of canine athletes need to continually read and evaluate new
scientific studies to ensure that we are taking the most appropriate care of our performance dogs. This article
provides evidence through a number of recent studies to suggest that veterinarians and owners working with
canine athletes should revisit the standard protocol in which all dogs that are not intended for breeding are
spayed and neutered at or before 6 months of age.
Orthopedic Considerations
A study by Salmeri et al in 1991 found that bitches spayed at 7 weeks grew significantly taller than those spayed
at 7 months, who were taller than those not spayed (or presumably spayed after the growth plates had closed).(1)
A study of 1444 Golden Retrievers performed in 1998 and 1999 also found bitches and dogs spayed and
neutered at less than a year of age were significantly taller than those spayed or neutered at more than a year of
age.(2) The sex hormones, by communicating with a number of other growth-related hormones, promote the
closure of the growth plates at pubjerty (3), so the bones of dogs or bitches neutered or spayed before puberty
continue to grow. Dogs that have been spayed or neutered well before puberty can frequently be identified by
their longer limbs, lighter bone structure, narrow chests and narrow skulls. This abnormal growth frequently
results in significant alterations in body proportions and particularly the lengths (and therefore weights) of certain
bones relative to others. For example, if the femur has achieved its genetically determined normal length at 8
months when a dog gets spayed or neutered, but the tibia, which normally stops growing at 12 to 14 months of
age continues to grow, then an abnormal angle may develop at the stifle. In addition, with the extra growth, the
lower leg below the stifle likely becomes heavier (because it is longer), and may cause increased stresses on the
cranial cruciate ligament. In addition, sex hormones are critical for achieving peak bone density.(4) These
structural and physiological alterations may be the reason why at least one recent study showed that spayed and
neutered dogs had a higher incidence of CCL rupture.(5) Another recent study showed that dogs spayed or
neutered before 5 1/2 months had a significantly higher incidence of hip dysplasia than those spayed or neutered
after 5 1/2 months of age, although it should be noted that in this study there were no standard criteria for the
diagnosis of hip dysplasia.(6) Nonetheless, breeders of purebred dogs should be cognizant of these studies and
should consider whether or not pups they bred were spayed or neutered when considering breeding decisions.
Cancer Considerations
A retrospective study of cardiac tumors in dogs showed that there was a 5 times greater risk of
hemangiosarcoma, one of the three most common cancers in dogs, in spayed bitches than intact bitches and a
2.4 times greater risk of hemangiosarcoma in neutered dogs as compared to intact males.(7) A study of 3218
dogs demonstrated that dogs that were neutered before a year of age had a significantly increased chance of
developing bone cancer.(8) A separate study showed that neutered dogs had a two-fold higher risk of developing
bone cancer.(9) Despite the common belief that neutering dogs helps prevent prostate cancer, at least one study
suggests that neutering provides no benefit.(10) There certainly is evidence of a slightly increased risk of
mammary cancer in female dogs after one heat cycle, and for increased risk with each subsequent heat. While
about 30 % of mammary cancers are malignant, as in humans, when caught and surgically removed early the
prognosis is very good.(12) Luckily, canine athletes are handled frequently and generally receive prompt
veterinary care.
Behavioral Considerations
The study that identified a higher incidence of cranial cruciate ligament rupture in spayed or neutered dogs also
identified an increased incidence of sexual behaviors in males and females that were neutered early.(5) Further,
the study that identified a higher incidence of hip dysplasia in dogs neutered or spayed before 5 1/2 months also
showed that early age gonadectomy was associated with an increased incidence of noise phobias and
undesirable sexual behaviors.(6) A recent report of the American Kennel Club Canine Health Foundation reported
significantly more behavioral problems in spayed and neutered bitches and dogs. The most commonly observed
behavioral problem in spayed females was fearful behavior and the most common problem in males was
aggression.(12)
Other Health Considerations
A number of studies have shown that there is an increase in the incidence of female urinary incontinence in dogs
spayed early (13), although this finding has not been universal. Certainly there is evidence that ovarian hormones
are critical for maintenance of genital tissue structure and contractility.(14, 15) Neutering also has been
associated with an increased likelihood of urethral sphincter incontinence in males.(16) This problem is an
inconvenience, and not usually life-threatening, but nonetheless one that requires the dog to be medicated for life.
A health survey of several thousand Golden Retrievers showed that spayed or neutered dogs were more likely to
develop hypothyroidism.(2) This study is consistent with the results of another study in which neutering and
spaying was determined to be the most significant gender-associated risk factor for development of
hypothyroidism.(17) Infectious diseases were more common in dogs that were spayed or neutered at 24 weeks or
less as opposed to those undergoing gonadectomy at more than 24 weeks.(18) Finally, the AKC-CHF report
demonstrated a higher incidence of adverse reactions to vaccines in neutered dogs as compared to intact.(12)
I have gathered these studies to show that our practice of routinely spaying or neutering every dog at or before
the age of 6 months is not a black-and-white issue. Clearly more studies need to be done to evaluate the effects
of prepubertal spaying and neutering, particularly in canine athletes.
Currently, I have significant concerns with spaying or neutering canine athletes before puberty. But of course,
there is the pet overpopulation problem. How can we prevent the production of unwanted dogs while still leaving
the gonads to produce the hormones that are so important to canine growth and development? One answer
would be to perform vasectomies in males and tubal ligation in females, to be followed after maturity by
ovariohysterectomy in females to prevent mammary cancer and pyometra. One possible disadvantage is that
vasectomy does not prevent some unwanted behaviors associated with males such as marking and humping. On
the other hand, females and neutered males frequently participate in these behaviors too. Really, training is the
best solution for these issues. Another possible disadvantage is finding a veterinarian who is experienced in
performing these procedures. Nonetheless, some do, and if the procedures were in greater demand, more
veterinarians would learn them.
I believe it is important that we assess each situation individually. For canine athletes, I currently recommend that
dogs and bitches be spayed or neutered after 14 months of age.
References:
1. Salmeri KR, Bloomberg MS, Scruggs SL, Shille V.. Gonadectomy in immature dogs: effects on skeletal,
physical, and behavioral development. JAVMA 1991;198:1193-1203
2. http://www.grca.org/healthsurvey.pdf
3. Grumbach MM. Estrogen, bone, growth and sex: a sea change in conventional wisdom. J Pediatr Endocrinol
Metab. 2000;13 Suppl 6:1439-55.
4. Gilsanz V, Roe TF, Gibbens DT, Schulz EE, Carlson ME, Gonzalez O, Boechat MI. Effect of sex steroids on
peak bone density of growing rabbits. Am J Physiol. 1988 Oct;255(4 Pt 1):E416-21.
5. Slauterbeck JR, Pankratz K, Xu KT, Bozeman SC, Hardy DM. Canine ovariohysterectomy and orchiectomy
increases the prevalence of ACL injury. Clin Orthop Relat Res. 2004 Dec;(429):301-5.
6. Spain CV, Scarlett JM, Houpt KA. Long-term risks and benefits of early-age gonadectomy in dogs. JAVMA
2004;224:380-387.
7. Ware WA, Hopper DL. Cardiac tumors in dogs: 1982-1995. J Vet Intern Med 1999 Mar-Apr;13(2):95-103
8. Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters D, Cancer Epidemiol Biomarkers
Prev. 2002 Nov;11(11):1434-40
9. Ru G, Terracini B, Glickman LT. Host related risk factors for canine osteosarcoma. Vet J. 1998 Jul;156(1):31-
9.
10. Obradovich J, Walshaw R, Goullaud E. The influence of castration on the development of prostatic carcinoma
in the dog. 43 cases (1978-1985). J Vet Intern Med 1987 Oct-Dec;1(4):183-7
11. http://www.akcchf.org/pdfs/whitepapers/Biennial_National_Parent_Club_Canine_Health_Conference.pdf
12. Meuten DJ. Tumors in Domestic Animals. 4th Edn. Iowa State Press, Blackwell Publishing Company, Ames,
Iowa, p. 575
13. Stocklin-Gautschi NM, Hassig M, Reichler IM, Hubler M, Arnold S. The relationship of urinary incontinence to
early spaying in bitches. J. Reprod. Fertil. Suppl. 57:233-6, 2001
14. Pessina MA, Hoyt RF Jr, Goldstein I, Traish AM. Differential effects of estradiol, progesterone, and
testosterone on vaginal structural integrity. Endocrinology. 2006 Jan;147(1):61-9.
15. Kim NN, Min K, Pessina MA, Munarriz R, Goldstein I, Traish AM. Effects of ovariectomy and steroid
hormones on vaginal smooth muscle contractility. Int J Impot Res. 2004 Feb;16(1):43-50.
16. Aaron A, Eggleton K, Power C, Holt PE. Urethral sphincter mechanism incompetence in male dogs: a
retrospective analysis of 54 cases. Vet Rec. 139:542-6, 1996
17. Panciera DL. Hypothyroidism in dogs: 66 cases (1987-1992). J. Am. Vet. Med. Assoc., 204:761-7 1994
18. Howe LM, Slater MR, Boothe HW, Hobson HP, Holcom JL, Spann AC. Long-term outcome of gonadectomy
performed at an early age or traditional age in dogs. J Am Vet Med Assoc. 2001 Jan 15;218(2):217-21.
One Veterinarian’s Opinion
© 2005 Chris Zink DVM, PhD, DACVP
www.caninesports.com
Those of us with responsibility for the health of canine athletes need to continually read and evaluate new
scientific studies to ensure that we are taking the most appropriate care of our performance dogs. This article
provides evidence through a number of recent studies to suggest that veterinarians and owners working with
canine athletes should revisit the standard protocol in which all dogs that are not intended for breeding are
spayed and neutered at or before 6 months of age.
Orthopedic Considerations
A study by Salmeri et al in 1991 found that bitches spayed at 7 weeks grew significantly taller than those spayed
at 7 months, who were taller than those not spayed (or presumably spayed after the growth plates had closed).(1)
A study of 1444 Golden Retrievers performed in 1998 and 1999 also found bitches and dogs spayed and
neutered at less than a year of age were significantly taller than those spayed or neutered at more than a year of
age.(2) The sex hormones, by communicating with a number of other growth-related hormones, promote the
closure of the growth plates at pubjerty (3), so the bones of dogs or bitches neutered or spayed before puberty
continue to grow. Dogs that have been spayed or neutered well before puberty can frequently be identified by
their longer limbs, lighter bone structure, narrow chests and narrow skulls. This abnormal growth frequently
results in significant alterations in body proportions and particularly the lengths (and therefore weights) of certain
bones relative to others. For example, if the femur has achieved its genetically determined normal length at 8
months when a dog gets spayed or neutered, but the tibia, which normally stops growing at 12 to 14 months of
age continues to grow, then an abnormal angle may develop at the stifle. In addition, with the extra growth, the
lower leg below the stifle likely becomes heavier (because it is longer), and may cause increased stresses on the
cranial cruciate ligament. In addition, sex hormones are critical for achieving peak bone density.(4) These
structural and physiological alterations may be the reason why at least one recent study showed that spayed and
neutered dogs had a higher incidence of CCL rupture.(5) Another recent study showed that dogs spayed or
neutered before 5 1/2 months had a significantly higher incidence of hip dysplasia than those spayed or neutered
after 5 1/2 months of age, although it should be noted that in this study there were no standard criteria for the
diagnosis of hip dysplasia.(6) Nonetheless, breeders of purebred dogs should be cognizant of these studies and
should consider whether or not pups they bred were spayed or neutered when considering breeding decisions.
Cancer Considerations
A retrospective study of cardiac tumors in dogs showed that there was a 5 times greater risk of
hemangiosarcoma, one of the three most common cancers in dogs, in spayed bitches than intact bitches and a
2.4 times greater risk of hemangiosarcoma in neutered dogs as compared to intact males.(7) A study of 3218
dogs demonstrated that dogs that were neutered before a year of age had a significantly increased chance of
developing bone cancer.(8) A separate study showed that neutered dogs had a two-fold higher risk of developing
bone cancer.(9) Despite the common belief that neutering dogs helps prevent prostate cancer, at least one study
suggests that neutering provides no benefit.(10) There certainly is evidence of a slightly increased risk of
mammary cancer in female dogs after one heat cycle, and for increased risk with each subsequent heat. While
about 30 % of mammary cancers are malignant, as in humans, when caught and surgically removed early the
prognosis is very good.(12) Luckily, canine athletes are handled frequently and generally receive prompt
veterinary care.
Behavioral Considerations
The study that identified a higher incidence of cranial cruciate ligament rupture in spayed or neutered dogs also
identified an increased incidence of sexual behaviors in males and females that were neutered early.(5) Further,
the study that identified a higher incidence of hip dysplasia in dogs neutered or spayed before 5 1/2 months also
showed that early age gonadectomy was associated with an increased incidence of noise phobias and
undesirable sexual behaviors.(6) A recent report of the American Kennel Club Canine Health Foundation reported
significantly more behavioral problems in spayed and neutered bitches and dogs. The most commonly observed
behavioral problem in spayed females was fearful behavior and the most common problem in males was
aggression.(12)
Other Health Considerations
A number of studies have shown that there is an increase in the incidence of female urinary incontinence in dogs
spayed early (13), although this finding has not been universal. Certainly there is evidence that ovarian hormones
are critical for maintenance of genital tissue structure and contractility.(14, 15) Neutering also has been
associated with an increased likelihood of urethral sphincter incontinence in males.(16) This problem is an
inconvenience, and not usually life-threatening, but nonetheless one that requires the dog to be medicated for life.
A health survey of several thousand Golden Retrievers showed that spayed or neutered dogs were more likely to
develop hypothyroidism.(2) This study is consistent with the results of another study in which neutering and
spaying was determined to be the most significant gender-associated risk factor for development of
hypothyroidism.(17) Infectious diseases were more common in dogs that were spayed or neutered at 24 weeks or
less as opposed to those undergoing gonadectomy at more than 24 weeks.(18) Finally, the AKC-CHF report
demonstrated a higher incidence of adverse reactions to vaccines in neutered dogs as compared to intact.(12)
I have gathered these studies to show that our practice of routinely spaying or neutering every dog at or before
the age of 6 months is not a black-and-white issue. Clearly more studies need to be done to evaluate the effects
of prepubertal spaying and neutering, particularly in canine athletes.
Currently, I have significant concerns with spaying or neutering canine athletes before puberty. But of course,
there is the pet overpopulation problem. How can we prevent the production of unwanted dogs while still leaving
the gonads to produce the hormones that are so important to canine growth and development? One answer
would be to perform vasectomies in males and tubal ligation in females, to be followed after maturity by
ovariohysterectomy in females to prevent mammary cancer and pyometra. One possible disadvantage is that
vasectomy does not prevent some unwanted behaviors associated with males such as marking and humping. On
the other hand, females and neutered males frequently participate in these behaviors too. Really, training is the
best solution for these issues. Another possible disadvantage is finding a veterinarian who is experienced in
performing these procedures. Nonetheless, some do, and if the procedures were in greater demand, more
veterinarians would learn them.
I believe it is important that we assess each situation individually. For canine athletes, I currently recommend that
dogs and bitches be spayed or neutered after 14 months of age.
References:
1. Salmeri KR, Bloomberg MS, Scruggs SL, Shille V.. Gonadectomy in immature dogs: effects on skeletal,
physical, and behavioral development. JAVMA 1991;198:1193-1203
2. http://www.grca.org/healthsurvey.pdf
3. Grumbach MM. Estrogen, bone, growth and sex: a sea change in conventional wisdom. J Pediatr Endocrinol
Metab. 2000;13 Suppl 6:1439-55.
4. Gilsanz V, Roe TF, Gibbens DT, Schulz EE, Carlson ME, Gonzalez O, Boechat MI. Effect of sex steroids on
peak bone density of growing rabbits. Am J Physiol. 1988 Oct;255(4 Pt 1):E416-21.
5. Slauterbeck JR, Pankratz K, Xu KT, Bozeman SC, Hardy DM. Canine ovariohysterectomy and orchiectomy
increases the prevalence of ACL injury. Clin Orthop Relat Res. 2004 Dec;(429):301-5.
6. Spain CV, Scarlett JM, Houpt KA. Long-term risks and benefits of early-age gonadectomy in dogs. JAVMA
2004;224:380-387.
7. Ware WA, Hopper DL. Cardiac tumors in dogs: 1982-1995. J Vet Intern Med 1999 Mar-Apr;13(2):95-103
8. Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters D, Cancer Epidemiol Biomarkers
Prev. 2002 Nov;11(11):1434-40
9. Ru G, Terracini B, Glickman LT. Host related risk factors for canine osteosarcoma. Vet J. 1998 Jul;156(1):31-
9.
10. Obradovich J, Walshaw R, Goullaud E. The influence of castration on the development of prostatic carcinoma
in the dog. 43 cases (1978-1985). J Vet Intern Med 1987 Oct-Dec;1(4):183-7
11. http://www.akcchf.org/pdfs/whitepapers/Biennial_National_Parent_Club_Canine_Health_Conference.pdf
12. Meuten DJ. Tumors in Domestic Animals. 4th Edn. Iowa State Press, Blackwell Publishing Company, Ames,
Iowa, p. 575
13. Stocklin-Gautschi NM, Hassig M, Reichler IM, Hubler M, Arnold S. The relationship of urinary incontinence to
early spaying in bitches. J. Reprod. Fertil. Suppl. 57:233-6, 2001
14. Pessina MA, Hoyt RF Jr, Goldstein I, Traish AM. Differential effects of estradiol, progesterone, and
testosterone on vaginal structural integrity. Endocrinology. 2006 Jan;147(1):61-9.
15. Kim NN, Min K, Pessina MA, Munarriz R, Goldstein I, Traish AM. Effects of ovariectomy and steroid
hormones on vaginal smooth muscle contractility. Int J Impot Res. 2004 Feb;16(1):43-50.
16. Aaron A, Eggleton K, Power C, Holt PE. Urethral sphincter mechanism incompetence in male dogs: a
retrospective analysis of 54 cases. Vet Rec. 139:542-6, 1996
17. Panciera DL. Hypothyroidism in dogs: 66 cases (1987-1992). J. Am. Vet. Med. Assoc., 204:761-7 1994
18. Howe LM, Slater MR, Boothe HW, Hobson HP, Holcom JL, Spann AC. Long-term outcome of gonadectomy
performed at an early age or traditional age in dogs. J Am Vet Med Assoc. 2001 Jan 15;218(2):217-21.