Saber Tails
ISummer 2015
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55
The Role of Neutering in Cancer Development
Annette N. Smith, DVM, MS
Vet Clin Small Anim 44 (2014) 965-975
Many PBGVs in the PBGVCA community are reproductively
intact because they are being actively shown or are in
breeding programs. What about the dogs who are retired
from the ring, are no longer being bred or are family pets?
The advantages of neutering the latter group of dogs are well
documented. A spayed bitch doesn’t worry about pyometra,
isn’t surprised by an unplanned pregnancy and no longer
has to shop in the feminine hygiene aisle of the supermarket.
A castrated male is less likely to roam, fight or mount
inappropriately. In addition, neutering leads to decreased
risk of mammary, ovarian and uterine tumors of the female,
and testicular tumors of the male. What’s not to like?
Dr. Annette Smith is Professor of Clinical Sciences at the
Auburn University College of Veterinary Medicine. Her
clinical specialty is oncology. Dr. Smith has gathered
information from published studies on the effect of
surgical sterilization on the occurrence of cancer.
Her article cites several studies that have found an
increased risk of certain tumor types in surgically altered
dogs. For example, osteosarcoma is more common in large
and giant breeds, and neutered dogs of those breeds have a
two-fold high risk for this diagnosis. Several studies have
found the risk of hemangiosarcoma is many-fold greater in
neutered females than intact, whereas the risk for males
was less. The risks for both lymphoma and transitional cell
carcinoma are higher in neutered dogs of both sexes.
Dr. Smith cites a study published in 2013 that examined
the causes of death among more than 40,000 dogs presented
to North American veterinary teaching hospitals from 1984
to 2004 (Hoffman, Creevy, and Promislow, 2013, PLOS ONE
8:e61082). The authors found a slight increase in life
expectancy in sterilized dogs as compared to intact;
however, they found large differences in the cause of death.
Sterilized dogs of both sexes were much less likely to die of
infectious disease (i.e., parvovirus, heartworm, canine
distemper, intestinal parasites), trauma, vascular disease and
degenerative disease. In contrast, the sterilized dogs were
more likely to die of cancer (i.e. transitional cell carcinoma,
osteosarcoma, lymphoma, mast cell tumors) and immune-
mediated disease. The relationship between sterilization and
risk of cancer was seen in all size classes of dogs.
The bottom line is that neutering has positive effects
on behaviors, noncancerous diseases and lifespan that
outweigh the increased risk of cancer. It is unclear why
sterilization has an effect on the risk for cancers outside of
the reproductive system. Owners should be aware of the risk
of cancer in their neutered hounds and discuss this with
their veterinarians. Dr. Smith concludes by saying “In
un-owned, shelter or rescue populations, the population
benefits of neutering likely outweigh any potential for
increasing cancer risk. For owned animals, veterinarians will
need to discuss the pros and cons for each individual and
determine the best strategy for that pet based on breed,
lifestyle, longevity expectations, concurrent diseases, cancer
risks, other considerations for intact and sterilized dogs, and
owner preferences.”
When do our PBGVs transition from being adults to seniors?
The American Animal Hospital Association suggests that
dogs are considered to be seniors when they are in the last
25 percent of their predicted lifespan. The typical healthy
PBGV has a lifespan of about 12 to 14 years, which means
that PBGVs transition from adult to senior around 10 years
of age.
How do the nutritional needs of our PBGVs change as
they age? This question was addressed by Dr. Jennifer
Larsen, Associate Professor of Clinical Nutrition at the
University of California Davis School of Veterinary Medi-
cine, and Dr. Amy Farcas, of the University of Pennsylvania
School of Veterinary Medicine Clinical Nutrition Service.
Drs. Larsen and Farcas note that older dogs may have
normal physiologic changes that occur with aging and
pathologic changes due to disease. Both types of changes
may benefit from nutritional intervention.
Normal physiological changes associated with an aging
PBGV (as well as his/her aging owner!) include changes in
body composition and reduced metabolic rate. In general,
older dogs have a reduced lean body mass and resting
energy requirement accompanied by an increase in body
fat mass. It is important to monitor body condition since
obesity can exacerbate age-related diseases. Surprisingly,
senior dogs have a higher prevalence of being underweight,
which may be due to undiagnosed pathologic conditions.
Studies have shown that senior dogs absorb nutrients as well
as young dogs; however, their protein requirement increases
most likely due to increased protein turnover.
Many pet food manufacturers offer canine diets targeted
towards the senior population. It is important to be aware
that the ideal nutritional profile of a diet for senior dogs has
not been agreed upon. Thus, there is wide variation in
energy density, nutrients and supplements in the senior diet.
Pathologic changes in the senior dog that may respond to
nutrition include cognitive dysfunction, declining immunity
and degenerative joint disease. Studies have shown that a
diet enriched in anti-oxidants leads to improved behavior
score, social interactions, sleep patterns, agility, learning,
and recognition in dogs with cognitive dysfunction. Keeping
a PBGV mentally active with games that use his/her nose
may also be helpful. Dietary enrichment of anti-oxidants
and vitamins also improved some aspects of immunity as
measured by laboratory tests, although there was no
measure of immunity of dogs against infectious disease.
The prescription for preventing degenerative joint disease
in dogs is the same as for humans — maintain a healthy
weight, incorporate exercise into continued on next page
Nutrition of Aging Dogs
Jennifer A. Larsen, DVM, PhD and Amy Farcas, DVM, MS
Vet Clin Small Anim 44 (2014) 741-759