To neuter or not to neuter...
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 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, and that those spayed at 7 months had significantly delayed closure
of the growth plates 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 promote the closure of the
growth plates, 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 becomes heavier (because it is longer), causing
increased stresses on the cranial cruciate ligament. These structural alterations
may be the reason why at least one recent study has shown that spayed and
neutered dogs have a higher incidence of CCL rupture.(3) 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.(4) Breeders of purebred dogs should be concerned about these
two studies and particularly the latter, because they might make incorrect
breeding decisions if they consider the hip status of pups they bred that
were spayed or neutered early.
Cancer Considerations
There is a slightly increased risk of mammary
cancer if a female dog has one heat cycle. But my experience indicates that
fewer canine athletes develop mammary cancer as compared to those that damage
their cranial cruciate ligaments. In addition, only about 30 % of mammary
cancers are malignant and, as in humans, when caught and surgically removed
early the prognosis is very good.(5) Since canine athletes are handled frequently
and generally receive prompt veterinary care, mammary cancer is not quite
the specter it has been in the past. 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.(6) 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, a cancer that is much more life-threatening than
mammary cancer, and that affects both genders.(7) A separate study showed
that neutered dogs had a two-fold higher risk of developing bone cancer.(8)
Despite the common belief that neutering dogs helps prevent prostate cancer,
at least one study suggests that neutering provides no
benefit.(9)
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.(3) 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.(4) 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.(10) Yet another study showed
that unneutered males were significantly less likely than neutered males
to suffer cognitive impairment when they were older.(11) Females were not
evaluated in that study.
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.(12) Interestingly, neutering also has been associated with an increased
likelihood of urethral sphincter incontinence in males.(13) 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.(14) 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.(15) Finally, the AKC-CHF report demonstrated a higher
incidence of adverse reactions to vaccines in neutered dogs as compared to
intact. 0) For these reasons, I have significant concerns with spaying or
neutering dogs before puberty, particularly for the canine athlete. And frankly,
if something were healthier for the canine athlete, would we not also want
that for pet dogs as well? 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? The answer is 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, it has been my experience
that females and neutered males actively 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. 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 the dog under their control at all times and to not
breed it, I do not recommend spaying or neutering before 14 months of age.
In the case of dogs that might be going to less vigilant families, vasectomy
and tubal ligation will allow proper growth while preventing unwanted
pregnancies.
References:
Salmeri KR, Bloomberg MS, Scruggs SL, Shille V.. Gonadectomy in immature
dogs: effects on skeletal, physical, and behavioral development. JAVMA
1991;198:1193-1203
http://www.grca.org/healthsurvey.pdf
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.
Spain CV, Scarlett JM, Houpt KA. Long-term risks and benefits of early-age
gonadectomy in dogs. JAVMA 2004;224:380-387.
Meuten DJ. Tumors in Domestic Animals. 4th Edn. Iowa State Press, Blackwell
Publishing Company, Ames, Iowa, p. 575
Ware WA, Hopper DL. Cardiac tumors in dogs: 1982-1995. J Vet Intern Med 1999
Mar-Apr;13(2):95-103
Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters D,
Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1434-40
Ru G, Terracini B, Glickman LT. Host related risk factors for canine
osteosarcoma. Vet J. 1998 Jul;156(1):31-9.
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
http://www.akcchf.org/pdfs/whitepapers/Biennial_National_Parent_Club_Canine_He
alth_Conference.pdf
Hart BL. Effect of gonadectomy on subsequent development of age-related
cognitive impairment in dogs. J Am Vet Med Assoc. 2001 Jul 1;219(1):51-6.
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
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
Panciera DL. Hypothyroidism in dogs: 66 cases (1987-1992). J. Am. Vet. Med.
Assoc., 204:761-7 1994
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.
