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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: - Asexual reproduction - Cellular fission - Mitosis - Meiosis - Crossing Over - Diploid - Haploid - Spermatogenesis - Scrotum - Denature - Seminiferous Tubules - Lumen - Primordial Germ Cell - Cytokinesis - Sertoli Cells - Blood-testis Barrier - Epididymus - Vas Deferens - Polar Body If your project was late, describe why - Ovum - Follicle - Corpus Luteum - Fallopian Tube/Oviduct - Ovariohysterectomy - 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.