Download Spaying and Neutering Dogs and Cats by C. Kohn, WHS

Spaying and Neutering Dogs and Cats
Name:
Hour
Date Assignment is due:
by C. Kohn, WHS
Date:
Why late?
Day of Week
Date
If your project was late, describe why
Learning Objectives: Upon completing this assignment, you should be able to…
-
T
Describe why spaying and neutering is a humane choice
Understand the function and physiology of the reproductive organs of dogs and cats
Explain why sexual reproduction is biologically advantageous
Understand the basic process of removing the sexual organs
Explain how the process of spaying and neutering can prevent sexual reproduction without inhibiting any other physiological processes
Describe complications that can arise from spaying and neutering as well as the symptoms of these problems
Correctly use veterinary terms related to the processes of spaying and neutering
raditionally, TV shows and movies portray spaying and neutering as difficult choices. The owners (particularly the
male owners) cringe at the thought of surgically removing the sexual organs. While this may make for
entertaining comedic performances on camera, in reality spaying and neutering is simply the right choice.
In addition to preventing the addition of millions of unwanted (and often neglected or abused) dogs and cats, neutering
also serves to reduce testicular cancer and prostate disease in males. In females, spaying prevents pyometra (puss-filled
uterus) and breast cancer. The sooner spaying or neutering is safely performed, the less likely the animal will be to
develop surgical complications.
Neutered or spayed animals also tend to make better pets. Both dogs and cats are much more likely to roam when in
heat (a dog or cat is in heat when they are sexually aroused and ready to mate). This not only makes them disagreeable
or loud when around your home, but also more likely to be lost, injured, or killed if and when they leave your home. It is
not an overstatement to say that fewer dogs and cats would be hit by cars if more were spayed and neutered.
Finally, a neutered or spayed pet is going to cause fewer problems economically, socially, and even physically. An unneutered dog can become more aggressive and can pose a biting risk. Male dogs may mount furniture or human legs
when aroused and male cats may spay strong-smelling urine.
Un-spayed females pose similar problems in both dogs and cats. A female cat will go into heat every 3 weeks. During
this 4-5 day period, the animal can meow loudly and will urinate more frequently. Female dogs will excrete discharge
for up to a week. In addition, both female dogs and cats will attract the unwanted attention of other males.
The Function of the Sexual Organs
Before explaining how to remove the sexual organs, let’s first begin by explaining how the sexual organs actually
function. This will not be a “birds and bees” kind of talk…rather this will be a tour of the male and female reproductive
tracts from beginning to end.
Some living organisms reproduce asexually. In other words, these species can create their own offspring without a
mate and pass on all its genes to the offspring. For example, bacterial cells can simply double their genetic material and
divide into two cells in a process called cellular fission. Your own cells undergo this same process in mitosis when your
DNA is doubled and divided equally between two daughter cells.
Some multi-celled organisms can also reproduce asexually. For example,
the hydra (the relative of some jellyfishes) can create “buds”, or
miniature copies of itself with the exact same DNA that will grow to
become copies of the parent.
So why bother reproducing sexually? After all, it might seem easier to
simply create a copy of yourself and have it over with. Some animals
exhaust large amounts of energy to attract and keep a mate. Male
peacocks are far more prone to predation because of their elaborate
Figure 1 Hydra budding
colors meant solely for sexually attracting a female. Many male
mammals will fight to the point of exhaustion and injury to attract a
mate. Furthermore, sexual reproduction can also increase the transmission of disease and parasites. Simply put, sexual
reproduction can be a huge liability to an animal.
However, sexual reproduction does have benefits, and these benefits usually far outweigh the costs. The major
disadvantage to asexual reproduction (or cloning) is that genetic diversity is reduced. Genetic diversity is hugely
valuable to a species. It makes a species less susceptible to disease. It allows for new traits and adaptations to arise. It
enables a species to change over time depending on selection pressures from the environment. It enables a species to
adapt to future selection pressures that do not even exist yet.
Mitosis and Meiosis
In order for sexual reproduction to occur, we must avoid one crucial stumbling-block: how do we combine two
individual’s DNA without doubling the amount of DNA in the offspring? As you can imagine, this would be a huge
problem. For example, a cat has 38 chromosomes (a chromosome is a bundle of DNA). If a male and female cat were to
sexually reproduce without reducing their genetic material, their offspring would have 76 chromosomes, and the next
generation would have 152 chromosomes!
Because of this problem, mitosis (or cellular cloning) does not work for sexual cells like sperm and eggs. Instead, a
different process is used to create the sperm and egg cells were are familiar with. Unlike mitosis, in which a cell divides
into two identical cells, sperm and egg cells are created through meiosis. Meiosis is complex process in which multiple
cells are created, each with a reduced amount of genetic material. To use scientific terms, meiosis is necessary to turn a
cell from diploid (2 copies of every gene) into haploid cell (a cell with one copy of every gene).
Each of your regular cells has two copies of every gene. This means that no matter what trait you have in your body,
from eye color to ear lobes to your ability to break down lactose, you have twice the genes you need to perform this
process. This is because you get one copy of each gene from each of your parents. Both your mom and your dad gave
you a gene for eye color. Maybe only one of those genes was expressed, but you have both nonetheless.
In sexually reproducing species, meiosis is the process in which the cells with 2 copies of every gene (diploid cells) are
reduced to cells with one copy of every gene (haploid cells). This way, when a
sperm fuses with an egg, the newly formed offspring is once again diploid.
So how does meiosis turn a diploid cell into a haploid cell? Let’s begin with
simpler process of spermatogenesis, or the creation of sperm. Male dogs, like
most mammals, have two testes that are separated by connective tissue in
their scrotum. Production of sperm cells occurs in both testes. Sperm cells
cannot survive at body temperature and will denature (their proteins will
unfold) if they are kept at body temperature for too long. The scrotum, a sac-
like structure that contains the testes, will ascend or descend to keep the temperature of the forming sperm just below
the animal’s body temperature.
Inside each testis is a collection of specialized cells. Small lengthy tubes called Seminiferous Tubules coil inside the
testes. At the outside edge of each seminiferous tubule, a diploid cell begins to undergo meiosis. By the time that cell
reaches the hollow inside (lumen) of the tubule, it will have developed into multiple individual sperm cells.
The process begins with a primordial germ cell. A germ cell is simply a regular cell of the body that becomes a sperm or
egg cell. This germ cell is diploid, with two copies of every gene. The germ cells divide through mitosis to become
spermatogonia, or the stem cells that create sperm cells. Spermatogonia will differentiate (specialize) to become
spermatocytes. By this time, one germ cell will have become 4 spermatocytes. Once the germ cells have become
spermatocytes through mitosis and differentiation, the process of meiosis can begin.
Meiosis has two stages. In stage one (Meiosis I), the DNA is duplicated so that those 2 copies of every gene become 4
copies of every gene. We’ll call this four-copy stage 4N to keep it simpler. The DNA condenses into packages called
chromosomes. Chromosomes that are similar (all four of them), align next to each other. It is at this time that a very
crucial process occurs: the chromosomes exchange parts. Like 4th graders at lunch, each chromosome will exchange
portions so that each becomes slightly different genetically from each other. This process of mixing and matching genes
is called Crossing Over. It is also because of this that sexual cells (sperm and eggs) must be kept separate from the body
– because the DNA of the sperm and eggs are different than those of the body, the body would destroy those cells if
they were not kept separate. Crossing over provides a huge benefit in the form of additional genetic diversity to a
species. Entirely new genomes are created within the animal’s body even before intercourse occurs!
Once the chromosomes have finished exchanging their parts in the process of crossing over, they move to opposite ends
of the cell on tubular structures formed from the centrioles. The primary spermatocyte cell divides into two separate
cells. Unlike in mitosis, each of these cells has slightly varying DNA because of the process of crossing over. The process
of dividing a cell in half to create two new cells is called cytokinesis.
Each spermatocyte (now called a secondary spermatocyte after this first division), is diploid (2N). This should make
sense – the original primary spermatocyte doubled its DNA to become 4N. After this first round of cytokinesis, each
secondary spermatocyte would have half its DNA to become 2N.
In the second phase of Meiosis (Meiosis II), the steps are very similar, except that the DNA will not be doubled. This
way, when we undergo the second round of cytokinesis, each secondary spermatocyte will go from 2N to 1N, containing
only one copy of each gene. Meiosis is now finished, and the 1N copy of each spermatocyte now is called a spermatid.
Spermatids are like pre-sperm. They have undergone all the genetic modification they will need in order to become
functioning sperm and now must change physiologically. Because each spermatid is 1N, it will create a 2N offspring
when it combines with an egg that is also 1N.
From Spermatocyte to Sperm
By this point, we are also about halfway into the seminiferous tubule’s hollow inside. From this point on, the haploid
spermatids will now change physically instead of genetically. The spermatids will become more streamlined. They will
develop a tail from the centrioles that moved the chromosomes. This tail is powered by a wrapping band of
mitochondria. They will form an acrosomal cap. This structure, which envelops the head of the sperm, is crucial because
it contains the enzymes that will break down the tough outer ‘shell’ of the egg so that the DNA of the sperm can fuse
with the DNA of the egg to conceive the offspring.
The Journey Outward
By this time (65-75 days), the spermatids have become fully formed sperm cells. They move into the lumen of the
seminiferous tubules. Because sperm
cells are different genetically from
the rest of the cells of the body, they
must be kept separate from the
blood (or the white blood cells would
destroy the sperm). The sertoli cells
which make the seminiferous tubules
also protect and defend the
developing sperm cells by keeping
the sperm separated from the rest of
the body via the blood-testis barrier.
Sertoli cells are sort of like “nurse
cells” to sperm. Not only do they
support the process of
spermatogenesis, they also produce
fluid to move and nourish the sperm
cells once they are released into the
lumen of the seminiferous tubule.
This is necessary because the fluid that normally does this for the body’s cells (blood) must be kept separate or the
sperm cells would be destroyed.
From the seminiferous tubules, the sperm
pass into the coiled tubes of the epididymis.
For the couple weeks that the sperm reside
in the epididymis, they become motile and
able to fertilize an egg. Here the sperm cells
will wait until ejaculation. During
ejaculation, sperm enter the muscular vas
deferens and are propelled forward. The
vas deferens meets a second tubule, called
the seminal vesicle. This structure secretes
a fluid produced by the prostrate, the
Cowper’s or bulbourethtral gland, and the
seminal vesicle itself. This fluid, or semen,
is thick, yellowish, and has a high pH to
protect the sperm in the acidic female
reproductive tract. It contains fructose
sugar to provide the sperm with the energy they need to propel forward into the female reproductive tract.
The ejaculatory duct forms where the vas deferens meets the seminal vesicle. The ejaculatory duct moves sperm and
semen into the urethra, where it is propelled into the female during intercourse.
Castration
Castration in pets is a relatively straightforward procedure. On the day of the operation, the dog will undergo blood
work to check for problems that might affect the operation. A sedative is given, and the dog undergoes anesthesia.
Once asleep, a tube is placed down the dog’s throat to ensure that the animal can breathe throughout the operation.
The tube will deliver both oxygen and a predetermined amount of anesthesia to keep the animal under throughout the
operation.
The scrotum is shaved and scrubbed to prevent
infection. An incision is made in front of the
scrotum, and both testes are removed through
the incision. The cords leading to the testes are
tied off surgically, and the wound is sutured. A
pain reliever will be injected at the site of
operation, and the animal will be brought out of
anesthesia. Under normal circumstances, the
animal will be able to go home that same day.
The patient will be given pain relief medication
for home administration. Most dogs will not
realize that anything has happened. However,
some nausea can occur and it is not unusual for a
dog to refuse food for a day or two after the
operation. If the dog licks or bites at the stitches,
it will need an Elizabethan collar. Activity should
be restricted during the week after the operation to prevent swelling or the accumulation of fluid. Stitches will be
removed 10-14 days after the surgery. It is important that a qualified professional removes the stitches in order to check
for any complications.
After the Surgery
You may wonder what happens to the rest of the organs after surgery. After all, only the testes (containing the
seminiferous tubules made of sertoli cells) are removed. What about the glands, the production of semen, and the rest
of the male reproductive tract?
While those structures are still in place after castration, their “signals” to perform came from the testes. Therefore, they
will be largely inactive after castration and do not need to be removed. In general, a dog or cat’s life will be largely
unaffected by castration. Aside from sexual activity, the rest of their life will go on as if nothing had changed (and to
them, nothing has changed as far as they know). In addition, the reduced sexual urges of your pet combined with less
aggressive behavior, less urine marking, less mounting, the reduced occurrence of disease and disorder, and the reduced
likelihood of accidents or runaways will make your relationship with your pet happier, more affordable, and likely
longer.
Female Reproduction
Eggs are created through meiosis much like sperm cells are. However, the production of eggs differs from the
production of sperm in a few key ways:
1. All the eggs of a female are created prior to birth. Unlike
sperm cells, which are created throughout a male’s lifetime, a
female has a limited number of eggs. Her total number of
fertile eggs will decrease with each ovulation.
2. Unlike spermatogenesis, in which a 4N primary spermatocyte
creates two equal 2N secondary spermatocytes, which creates
a total of four 1N spermatids, oogensis has unequal
cytokinesis. This is a fancy way of saying that each time the
cells that create the egg divide, they only create one useable
cell. More will be said on this later.
3. Oogenesis (the creation of egg cells) has ‘resting periods’.
Unlike spermatogenesis, which is like a nonstop assembly line,
the production of eggs is interrupted.
Like spermatogenesis, oogenesis begins with a regular 2N diploid body
cell. This cell, called a primordial germ cell will become specialized
after several rounds of mitosis to become an oogonium.
After enough specialization and transformation, the oogonium will
become an oocyte. The oocyte undergoes crossing over during
Meiosis 1. Again, crossing over is the exchange of sections of
chromosomes. The oocyte will be frozen at this stage from before
birth until the time in which it matures after the onset of puberty.
Once the oocyte in question begins the process of ovulation, it will
start up where it left off at the beginning stages of Meiosis I. Unlike
meiosis in spermatogenesis, however, there will not be two equal products. Instead, the cytokinesis of the primary
oocyte after Meiosis I will create two different cells. One will be the secondary oocyte with a diploid (2N) state. The
other product is a polar body. A polar body is a smaller cell with very little cytoplasm. While it contains diploid
chromosomes like the secondary oocyte, it cannot undergo conception. This is necessary because the structure that will
eventually become the egg must also become the first cell of the newly created offspring. The sperm only contributes
genetic material; the egg also serves as the source of every cell that will exist in the baby. Because of this, it must have
as much size and cytoplasm as possible to support this growth. The polar body will eventually be discarded by the
female’s body, along with the DNA it contains.
The diploid secondary oocyte must now undergo a
second round of meiosis (Meiosis II), which will
create a second polar body that is haploid (1N).
The results of cytokinesis in the secondary oocyte
are a haploid ootid, and a haploid polar body. The
ootid will eventually become the ovum, or egg cell
that will be fertilized by a sperm cell if intercourse
is successful. Thus, instead of four haploid
reproductive cells (such as we see in
spermatogenesis), oogenesis creates one fertile egg
cell and two discarded polar bodies. (The female
reproductive strategy is covered in far more detail
in Large Animal Science; because of its complexity,
we will not go into as much detail here).
After sexual maturation is finished, the brain will
release a cocktail of hormones to induce ovulation. In response to these hormones, several follicles start to grow. A
follicle is a saclike structure in the ovary that contains an egg cell. The number of follicles that mature in each ovulation
is related to the normal number of offspring produced by that species. In humans, normally only one follicle matures at
each ovulation. Dogs and cats, which have litters
of offspring, will mature several follicles per
ovulation.
When the egg or eggs are released, the follicle will
become a corpus luteum. The corpus luteum is
responsible for releasing the hormones that keep
the animal pregnant. If the animal senses that she
did not become pregnant, a separate hormone
will be released to regress the corpus luteum, end
the menstrual cycle, and restart ovulation.
During ovulation, the egg (ovum) will be released
from the ovary and travel into the fallopian tube
(also known as the oviduct). It is here in the
fallopian tube that sperm will fertilize an egg. The
fertilized eggs will wait about a week after
fertilization before moving through the uterine
horns and implanting into the uterus, where they
would mature into puppies or kittens.
Spaying a Dog or Cat
Spaying, or an ovariohysterectomy, is also a very common procedure. However, spaying a female is far more
complicated and involved than castrating a male. In this procedure, the ovaries, ducts, and uterus will all be removed.
Like castration, the animal must be put under anesthesia. The abdomen is clipped and sanitized. An incision is made on
the lowest portion of the abdomen along the midline where connective tissue lies. The midline is used because it will
cause minimal bleeding compared to other areas above the reproductive tract. Occasionally the incision must be made
in an area outside of the midline; an incision can still be made easily but it is much more likely that bleeding will occur
and cause complications.
Special care must be made not to cut into the
abdominal organs that lie just below the abdominal
connective tissue. The animal is typically on its back
in this procedure, and the uterus is generally found
along the spinal column. Once it is located, a uterine
horn is brought forward to the surface. A major
blood vessel, the ovarian artery, must be clamped so
that the animal does not bleed to death during the
operation. The same must be done for the ovarian
vein. Both are then sutured shut and cut near the
base of the ovary. The veterinarian must carefully
examine these vessels after cutting them to ensure
that the sutures will not fail; this would cause the
animal to bleed to death inside.
Once the blood supply to the ovaries and uterus has
been sutured (or ligated), the ovaries, the uterine
horn, and most of the body of the uterus above the
cervix are removed. The abdominal area is examined
for bleeding and if none is found, the incision is
sutured back together. Females typically are kept
overnight after a spaying procedure. This way the
animal can be monitored closely and can receive adequate levels of pain medication appropriate for this more intensive
procedure. Because spaying is a more intense procedure, it is also more susceptible to complications. With any
operating procedure, infection is always a concern. The risk of this is minimized by proper surgical preparation and
usually does not cause an issue in most pets.
Because a major blood vessel is incised during a spaying procedure, uncontrolled bleeding is a possible risk. This is
especially true in obese animals. Obesity makes the procedure much more difficult because of the fat deposits in the
connective tissue of the uterus and ovaries that obstruct access and visibility. The blood vessels can be much harder to
identify and the tissue will be harder to grasp.
Another possible complication is obstruction of a ureter. The ureters are the vessels leading from the kidneys carrying
urine to the bladder. If a ureter is caught in the sutures used to close blood vessels after the removal of the uterus and
ovaries, urine flow will become blocked. This can permanently damage a kidney leading to that ureter. In most cases,
complications from these routine procedures are rare. Far more common are the daily problems caused by pets that are
not spayed or neutered. Spaying your animal before her first heat will allow for a happier and safer animal.
Questions – Spaying and Neutering
Name:
Hour
Date Assignment is due:
Date:
Why late?
Day of Week
Date
Define the following terms in your own words:
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Asexual reproduction
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Cellular fission
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Mitosis
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Meiosis
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Crossing Over
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Diploid
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Haploid
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Spermatogenesis
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Scrotum
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Denature
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Seminiferous Tubules
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Lumen
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Primordial Germ Cell
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Cytokinesis
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Sertoli Cells
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Blood-testis Barrier
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Epididymus
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Vas Deferens
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Polar Body
If your project was late, describe why
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Ovum
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Follicle
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Corpus Luteum
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Fallopian Tube/Oviduct
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Ovariohysterectomy
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Ligated
1. Name two health benefits of spaying female pets.
2. Name two health benefits of neutering male pets
3. What are three ways in which spaying or neutering can make for more enjoyable pets?
i.
ii.
iii.
4. Why would a species reproduce sexually when asexual reproduction entails much more energy, effort, and risk?
Provide three reasons that sexual reproduction is more common than asexual reproduction.
5. Why can’t sperm and egg cells be produced through mitosis?
6. How many copies of each gene do sperm and egg cells have when they are fully created? Why is this necessary?
7. Why are testes found on the outside of the body while ovaries are found on the inside?
8. As a spermatogonium passes from the outside edge of the sertoli cells in the seminiferous tubules to the inside
lumen, what happens?
9. What is crossing over?
a. How does crossing over enable a species to have more genetic diversity?
b. In what stage of Meiosis does crossing over occur?
10. For each of the following cell types, explain whether it is haploid, diploid, or tetraploid (i.e. 1N, 2N, or 4N):
a. Spermatogonium
b. Primary Spermatocyte
c. Secondary Spermatocyte
d. Spermatid
e. Sperm
11. Sperm and egg cells must be kept separate from the rest of the body. Why?
12. What is added to the sperm cells as they travel from the vas deferens to the urethra? Explain after each
structure what is contributed:
a. Seminal Vesicles
b. Prostate Gland
c. Cowper’s Gland
13. Semen, the fluid that supports sperm cells, has a high pH and contains fructose sugar. Why?
14. Where is the incision made for a castration procedure?
15. Why won’t the organs after the vas deferens have to be removed during castration?
16. How soon can a dog or cat go home after castration?
17. What are three differences between oogenesis and spermogenesis?
i.
ii.
iii.
18. What is a polar body? What happens to the polar bodies created by the ovaries?
19. Why does a female reproductive tract produce only one egg and two polar bodies instead of four eggs?
20. What determines the number of offspring born to a female of a species?
21. Where is the incision made for a spaying procedure?
a. Why is this area used?
22. What structures must be sutured and tied off before the ovaries and uterus can be removed? Why?
23. Why does obesity increase the risk of a spaying procedure?
24. What are three risks associated with spaying?
i.
ii.
iii.
25. In the space below, write 5 reasons why spaying and neutering is a responsible choice for a pet owner:
i.
ii.
iii.
iv.
v.