Newspapers, radio, and television commonly feature
articles about pet overpopulation. They stress the fact
that too many puppies and kittens are produced every year
and that there just are not enough potential owners to
go around. The obvious conclusion is that we should breed
fewer dogs and cats and produce fewer litters. The best
way to ensure that this occurs is through sterilization
procedures, so a larger percentage of dogs and cats are
incapable of breeding. Performing an ovariohysterectomy
(spaying) female animals is the best approach to decreasing
the number of puppies and kittens. Being veterinarians,
we also know that spaying and castrating pets are important
to the average pet owner because of the health and well
being of their animals. So, although you may spay your
animals in an effort to help control a national problem,
in doing so, you increase their chances of living long
Having a litter of puppies
may seem like a fun thing to do. Some even believe that
it helps their female dog, in some way, to develop more
completely or become a better pet. Neither is true.
Becoming pregnant and having a litter of puppies in
no way alters the maturity level of the dog, either
physically or mentally. In most cases, people find out
that it is hard to find good homes for all of the puppies,
regardless of the selling price. In addition, not all
pregnancies go smoothly. Difficult labor, puppy mortality,
and potential health problems in the mother, such as
uterine and mammary gland infections, can take all the
fun out of the experience. Most of the clients we have
worked with end up wishing they would never have allowed
their female to have a litter. Professional breeders
are prepared and equipped for the entire process and
it should generally be left to them.
female reproductive tract
The reproductive tract of the female dog begins with
the ovaries where the ova (or eggs) are produced. When
a female puppy is born, every egg that will be released
by her ovaries over her lifetime is already present.
They are, however, in an immature form and require further
development to reach a stage that can be fertilized
by sperm. When a dog's heat cycle starts, hormones stimulate
the maturation of some of the ova or eggs. The ova are
then released through the surface of the ovary and pass
into the oviducts. These are tiny tubes that run between
the ovaries and the horns of the uterus. It is within
the oviducts that fertilization (the union of the sperm
cell and ovum) occurs. The horns are the muscular section
of the uterus between the oviducts and the body of the
uterus. The uterine horns of dogs can vary greatly in
length and diameter. In the typical 40-pound dog, they
are normally about four inches long and the diameter
of a wooden pencil. When the animal is in heat, their
thickness will easily double and they may lengthen slightly.
During pregnancy, they will vary from 2.5 to 6 inches
in diameter and up to 24 inches in length. The horns
attach to the body of the uterus, a short common area
where the horns meet. The uterus ends at the cervix
of the dog. During pregnancy, most puppies develop within
the uterine horns, but one may reside within the body
of the uterus.
There are birth control
pills and medications manufactured specifically for
use in dogs. Most of these oral products can have serious
unwanted side effects, are expensive, and usually cannot
be used for long periods of time.
Since birth control pills
are not a viable option as a practical permanent form
of sterilization, the only option is surgical sterilization.
In the female, this would be either spaying (medically
referred to as ovariohysterectomy); a hysterectomy,
in which only the uterus is removed; or a tubal ligation.
These are different surgeries, but each one will prevent
future pregnancies if done correctly. Only an ovariohysterectomy
should be considered for the long-term health of your
An ovariohysterectomy (OHE) or spay is the complete
removal of the female reproductive tract. The ovaries,
oviducts, uterine horns, and the uterus are removed.
Not only does this procedure prevent the animal from
becoming pregnant, it also eliminates the twice-yearly
heat cycles. The surgery removes the source of production
of such hormones as estrogen and progesterone. These
hormones are responsible for stimulating and controlling
heat cycles and play a major role during pregnancy.
But they also have other effects on the body and some
of them are potentially harmful.
Ligation: A tubal ligation, whether
in veterinary or human medicine, only affects the oviducts.
These small structures are isolated during surgery and
then cut and tied off with suture material. This prevents
the ova from coming in contact with sperm cells or passing
into the horns of the uterus. In a hysterectomy, the
uterus is removed, but the ovaries remain. With either
procedure, the hormones that are normally produced by
the ovaries continue to be released to the rest of the
body. This is fairly important in humans. However, in
dogs it is a disadvantage.
Tubal ligations and hysterectomies,
through owner demand or veterinary preference, have
never been very popular in canine medicine. Some owners
see hysterectomy or tubal ligation as a way to sterilize
the pet, yet still allow her to experience heat cycles
and participate in mating. Because the ovaries remain
in the animal, the disadvantages of these procedures
are similar to those seen in intact dogs (dogs that
have not had surgical sterilization).
of tubal ligation or not spaying your dog
An OHE eliminates most, if not all,
of the female hormone production. In so doing, the real
advantages of this procedure are realized. In human
cases, great efforts are undertaken to maintain or restore
hormone production in the body, but the same is only
rarely true in canine practice. These hormones play
key roles in reproduction in the dog. However, they
can also have many unwanted side effects.
During the heat cycle there are behavior and hygienic
problems that develop. Females in heat will actively
search out male dogs and may attempt to escape from
the house or yard, putting them in the danger of traffic,
fights with other animals, etc. Often there is a sudden
influx of male dogs around the home and yard. These
dogs leave numerous droppings and spray plants and trees
with urine in an attempt to mark their new found territory.
Owners also need to contend with the vaginal bleeding
that typically lasts for 4 to 13 days.
is one of the primary causes of canine mammary cancer,
the most common malignant tumor in dogs. Animals that
are spayed prior to one year of age very rarely develop
this malignancy. Spaying a dog before her first heat
is the best way to significantly reduce the chance your
dog will develop mammary cancer. The risk of malignant
mammary tumors in dogs spayed prior to their first heat
is 0.05%. It is 8% for dog spayed after one heat, and
26% in dogs spayed after their second heat.
of the reproductive tract:
Tumors can occur in the uterus and ovaries. An OHE would,
of course, eliminate any possibility of these occurring.
Many female dogs have problems with a severe uterine
disease called pyometra following their heat cycles.
With this disorder, a normal three-ounce uterus can
weigh ten to fifteen pounds and be filled solely with
pus. Undetected, this condition is always fatal. Its
treatment requires either the use of expensive hormonal
and IV fluid therapy or an extremely difficult and expensive
ovariohysterectomy. A normal spay costs between $100
and $200, while one done to correct a pyometra can easily
cost $600 to over $1000, depending on complications.
The strain on the kidneys or heart in some of these
cases may be fatal or cause life long problems, even
after the infected uterus has been removed.
Some bitches fail to routinely go out of their heat
cycles correctly causing a condition we call 'false
pregnancy.' In these cases, even though the bitch may
not have mated with a male dog, her body believes it
is pregnant due to some incorrect hormonal stimulations
that it is receiving. The dog may just have some abdominal
swelling and/or engorgement of the mammary glands, but
in some cases, they will even make nests and snuggle
with socks or toys against their bodies. These animals
often experience no longterm serious problems, as the
behavior disappears when the circulating hormones return
to their appropriate levels. In others, we may see mastitis
(infection of the mammary glands), metritis (infection
of the uterus), or sometimes these cases develop into
full-blown pyometras. We recommend spaying dogs that
consistently have false pregnancies.
In dogs, hair does not grow continuously as in people,
but has a definite growing (anagen) and resting (telogen)
phase. Estrogen, which is increased during estrus, retards
or inhibits the anagen phase, so more hairs are in the
telogen phase. These resting hairs are more easily lost
because they are less firmly anchored. As a result,
the hair coat on many dogs suffers because of estrogen
surges that occur with heat cycles or whelping. Their
coats appear thin and the underlying skin is exposed
in many areas. It can take two to four months for the
hair to return to normal. Additionally, there are a
small number of female dogs that never develop a normal
hair coat because of the cycling hormones. Their coats
are consistently thin over the sides of their bodies
and these cases are sometimes confused diagnostically
with hypothyroid animals. The only treatment for these
dogs is an OHE.
In the United States, most dogs
are spayed between 5 and 8 months of age. Many humane
shelters and veterinarians are starting to spay female
animals at a younger age, even at 2 months. This early
spaying does not affect the growth rate, and there are
no appreciable differences in skeletal, physical, or
behavioral development between those animals spayed
early than those spayed at a more traditional age. It
must be remembered that younger animals may need different
anesthetics and are more prone to hypothermia (lower
than normal body temperature) during surgery. As long
as procedures are modified to account for these differences,
early neutering is very safe. In fact, animals spayed
at a younger age often have faster recoveries than those
spayed when they are older.
As can be seen from our discussion,
an ovariohysterectomy eliminates many medical and behavioral
problems that a tubal ligation does not. In fact, in
many dogs, an OHE probably adds years to their lives
or at least provides them with a more comfortable, less
stressful life. The OHE does its part in pet overpopulation,
but you, as the owner of an individual dog, should also
view it as a way to increase the length and quality
of your pet's life with you.
and Further Reading
Rutteman, GR; Withrow,
SJ; MacEwen, EG. Tumors of the mammary gland. In Withrow,
SJ; MacEwen, EG (eds). Small Animal Clinical Oncology.
W.B. Saunders Co. Philadelphia, PA; 2001 455-477.
Click here to read about Neutering