written by Ione L. Smith, DVM  January 20, 2000

Many people wonder about whether to spay or neuter their dogs. There are many points to consider, both for and against performing the procedures, and even more so for owners of dobermans because of their special needs. I hope this file will aid you in your decision.

People often use the term “spay” for females and “neuter” or “castrate” for males. However, technically speaking “neuter” or “alter” is proper for both sexes. For simplicity and clarity, I’ll use the words “sterilize” or “alter” throughout this document when I am referring to both spaying AND castration. “Intact” means that the dog has not been sterilized. Also, “bitch” is simply a term for a female dog and not an insult!

POINTS FOR STERILIZATION

{jb_greendisc}1.{/jb_greendisc} Spaying a young bitch prevents most mammary cancers.

Spaying a bitch before her first heat reduces her chances of contracting mammary cancer *200 times* compared to intact females. Spaying after the first heat, but before the second heat, will reduce a dog’s chance of contracting mammary cancer 13 times compared to intact females (Schneinder 1969, Schneinder 1970). Mammary cancer is the MOST common single type of cancer in intact bitches (Bastianello 1983, Kusch 1985).

{jb_greendisc}2.{/jb_greendisc} Spaying completely prevents problems with the uterus, such as pyometra and uterine cancer.

Pyometra is a serious infection of the uterus, which is usually expensive to treat and can often be fatal. It is a relatively common problem in intact bitches, especially after their heat cycles. Uterine cancer is relatively rare in dogs, but is also expensive to treat and often fatal. If the uterus is removed, these diseases will be prevented. Other diseases such as transmissible venereal tumor, cystic ovaries, mastitis, ovarian cancer, uterine torsion, and vaginal prolapse will also be eliminated.

{jb_greendisc}3.{/jb_greendisc} A sterilized animal will never produce an unwanted litter.

Millions of healthy dogs are killed every year in animal shelters across the nation. In 1991, approximately one THIRD of ALL dog and cat deaths in the country were due to healthy dogs being killed in shelters (Koltveit 1991, Olson 1991). Millions of healthy dogs are killed every year, simply because there are too many dogs and not enough homes. Roughly 11-19 MILLION cats and dogs are killed in shelters every year (National Council 1994).

Let’s face it. There are WAY too many unwanted dogs out there. Sterilized dogs will never add to the overpopulation problem! Sure, many people think of themselves as being responsible owners who would never accidentally let their dogs have a litter of puppies — but the shelters are full of puppies produced by other people who thought the very same thing. Accidents will happen. Bitches in heat will dig under fences, jump over them, scratch their way through doors, or even breed THROUGH fences if necessary; and male dogs will go to the same extremes to reach a female in heat.

{jb_greendisc}4.{/jb_greendisc} Intact females are in heat for two or three weeks at a time, usually twice a year.

During the time a bitch is in heat, it may be difficult to even walk her on a leash. Intact males will be seeking her out, and may even try to mate with her while you are on your walks. It will not be safe to even leave her inside a fenced yard during these times, since both intact males and females have been known to dig under or jump over fences, or even to breed through them.

While an intact female is in heat, she will be spotting blood all over the house unless she wears special protective garments. She may also be anxious, and frustrated during this time. Females will have to be separated from intact male playmates at these times, and will not be able to participate in obedience classes or competitions, play in the park, or take part in any of the other outdoor activities she usually enjoys. 

{jb_greendisc}5.{/jb_greendisc} Castration prevents most prostatic diseases in male dogs.

The prostate gland often becomes enlarged or infected in older intact male dogs. Diseases such as benign prostatic hyperplasia, acute or chronic prostatitis, perianal gland adenomas, and prostatic abscesses are common. Most of these diseases are eliminated if the dog is castrated (Cowan 1991, Krawiec 1992, 1994).

{jb_greendisc}6.{/jb_greendisc} Castration decreases aggression problems 

Aggression problems are most common in intact male dogs, including dominance aggression (Line 1986, Crowell-Davis 1991) as well as fear-related aggression (Galac 1997), aggression between males (Hopkins 1976), and other types of aggression (Neilson 1997). Castration is a valuable part of the treatment for aggression problems, and is helpful in preventing problems from occurring in the first place. Roughly 50%-75% of the dogs who are castrated because of aggression problems will show signicant improvements or complete disappearance of their aggression. Of course, training is also an important aid in preventing and/or treating these problems! (Askew 1992, Beaver 1983, Blackshaw 1991, Crowell-Davis 1991, Fry 1987, Knol 1989, Line 1986, Neilson 1997)

{jb_greendisc}7.{/jb_greendisc} Castrated males are less likely to roam, to mark furniture, or to practice other objectionable sexual behaviors.

Major behavioral benefits of castration have been known for many years, including decreases in aggression, roaming, mounting behavior, and “mischievous” behavior (Combemale 1929, Hart 1976, Heidenberger 1990, Hopkins 1976, Maarschalkerweerd, Neilson 1997, etc).

{jb_greendisc}8.{/jb_greendisc} Castration completely prevents testicular cancer in male dogs.

Testicular cancer is the most common cancer of the male reproductive tract, and is one of the most common cancers of intact males overall (Bastianello 1983, Kusch 1985). Once the testicles are removed during the castration procedure, the dog is free from the risk of this disease.

{jb_greendisc}9.{/jb_greendisc} Sterilization may help to prevent or treat other diseases, both infectious and non-infectious.

Some intact male dogs go through a “feminizing syndrome”, which is related to sex hormone production. This disease can not occur in dogs which were castrated at younger ages (Dorn 1985). Older intact males also tend to suffer from perineal hernias, which are also prevent by castration (Dorn 1985). Several other sex-hormone related diseases occur in both intact males and females, and these are also prevented by sterilization (Heider 1990).

Some breeds of dogs tend to suffer from skin problems which are prevented or treated by sterilization (Albanese 1997, Kunz). Altered dogs also have a lower risk of contracting some serious infectious diseases, such as echinococcosis (Bessonov 1986, Shal’menov, 1984), brucellosis (a disease which is transmitted in the dog by sexual contact), intestinal parasites (Coggins), and parvovirus (Houston 1992).

{jb_greendisc}10.{/jb_greendisc} Sterilization tends to increase an animal’s overall lifespan.

Altered animals are known to have a longer lifespan than intact animals overall. Sterilization appears to add approximately 2 years onto an animal’s life (Bronson 1981, Kraft 1996). 

POINTS AGAINST STERILIZATION

{jb_reddisc}1.{/jb_reddisc} Dogs may gain weight after being altered.

It is true that some animals may tend to gain weight after they are sterilized (Fettman 1997, Root 1995). The removal of the sex hormones may tend to slow an animal’s metabolism somewhat (Flynn 1996), although some studies have found no differences in weight between intact and sterilized animals (Salmeri 1991a). 

However, many dogs are altered just as they are reaching maturity. At this time in their lives, even dogs who are NOT altered will be gaining weight and slowing down a bit, so any change you see in your pet may not have anything to do with being sterilized. If you DO notice a weight gain after your dog is altered, simply decrease the amount of food you are feeding and increase the exercise your dog gets every day. 

{jb_reddisc}2.{/jb_reddisc} Altered dogs may be taller than intact dogs.

It is true that dogs who are sterilized before they have reached full maturity may be slightly taller than they would be if they had been left intact. Sex hormones influence the end of bone growth after puberty. Since the sex hormones never arrive in dogs which are altered before maturity, the bones tend to continue growing for longer than they would in the intact dog. However, this difference is very slight overall — and the dogs being altered are NOT show dogs, so a little extra height is of little significance. Also, there does not appear to be any difference in size between puppies sterilized very early (6-10 weeks) and those altered later (7 months) (Crenshaw 1995, Lieberman 1987).

{jb_reddisc}3.{/jb_reddisc} Sterilized dogs may become incontinent.

Some altered dogs may develop a problem with controlling their urine output. This is especially likely in females, but may also happen in males (Aaron 1996, Arnold 1997a). It is thought that this problem arises because the loss of sex hormones affects the strength of the urinary sphincter muscle (Gregory 1994). One researcher has claimed that incontinence may occur in as many as 20% of all spayed dogs (Arnold 1997a), but other vets believe this rate is much lower (Thrusfield 1993). 

Fortunately, the problem may be as minor as a few drops here and there, and it is usually easy to control with inexpensive drugs such as phenylpropanolamine (Arnold 1997b, Heughebaert 1988). Sometimes estrogen replacement may be necessary. Incontinence problems may last for the rest of the dog’s life. However, incontinence may also disappear after a few months or a few years (Heughebaert 1988, Arnold 1989). Also, keep in mind that older dogs will sometimes develop incontinence even if they are left intact, so incontinence is not always related to sterilization.

{jb_reddisc}4.{/jb_reddisc} Sterilized dogs are more likely to have problems with hypothyroidism.

A few dogs, especially bitches, may be more likely to have problems with decreased thyroid function after they are altered (Panciera 1994). Fortunately, thyroid problems are easy to treat with inexpensive thyroid supplements. Also, some intact dogs will also experience hypothyroidism, so most cases of hypothyroidism are not actually due to being sterilized.

{jb_reddisc}5.{/jb_reddisc} Bitches who are aggressive before being spayed may become more aggressive after being spayed.

This appears to be a valid concern for owners of aggressive bitches (O’Farrell 1990). However, it’s an easy problem to avoid. If you have an intact bitch who is already aggressive, think seriously about letting her remain intact. If your intact bitch is NOT aggressive, spaying her is not likely to MAKE her aggressive.

{jb_reddisc}6.{/jb_reddisc} Sterilization, especially spaying, is an invasive surgical procedure.

There are risks involved with any surgery, both from the surgery itself and from the anesthetic agent. However, the rate of complications is very low, and serious complications are especially rare. Especially with newer anesthetic agents like isofluorane and newer suture materials, there are rarely any serious problems. Significant complications of sterilization surgeries occur in roughly only 1-4% of surgeries (Pollari 1995, 1996). Also, the surgical procedure actually appears to be *safer* when performed in younger puppies, with less serious complications occurring overall in young puppies than in puppies altered at later ages (Fagella 1994).

{jb_reddisc}7.{/jb_reddisc} Sterilization is expensive.

Surgical costs may be as low as $25 or as high as $300, depending on the size and age of the dog, whether the dog is male or female, and the area of the country in which you live. There are low cost spay/neuter clinics in many areas these days for people who can’t otherwise afford the procedures. And in some areas you will actually SAVE money by sterilizing your dog, if licensing fees are lower for altered pets.

{jb_reddisc}8.{/jb_reddisc} The size of the external genitals may be smaller in dogs who are sterilized before puberty.

The penis of the male and the vagina of the female may be somewhat smaller in dogs who have been altered before puberty (Salmeri 1991a, 1991b). However, it is usually of little functional consequence to the dog. In a breed which is predisposed to urinary tract blockage, such as male dalmatians, this may be a problem; but in most breeds this is not likely to cause any medical complications. Very occasionally, bitches who were altered at very young ages may develop some skin irritation in the vulvar region (Jagoe 1988), but this also is not a common occurrence. 

MYTHS ABOUT STERILIZATION

1. A bitch ought to have at least one litter, or at least one heat, before being spayed.

The chances of mammary cancer in bitches gets much lower when they are spayed before their first heat, as discussed above under “points for sterilization”. Spaying a female before breeding her eliminates the chances of medical problems during a pregnancy or during birth or while rearing puppies. Also, puppies sterilized when they are very young (even as young as 7 weeks) actually have FEWER problems with the surgery than dogs who are neutered later (Faggella 1994, Howe 1997).

Before you let your dog “have just one litter”, spend some time volunteering at your local shelter and see all the puppies and dogs who must be killed daily. Letting your dogs breed only adds to the death toll, and to the vast numbers of dogs already suffering from genetic diseases like hip dysplasia, von Willebrand’s disease, progressive retinal atrophy, and many other diseases which can only be avoided by careful planning BEFORE breeding.

2. Castrating male dogs makes them more likely to get prostate cancer.

No, this is not true. There is apparently NO significant difference between the incidence of prostatic adenocarcinoma in intact males vs castrated males (Obradovich 1987). The only difference is an increased spread of the cancer to the lungs of the neutered dogs (Bell 1991). And MOST types of prostatic disease are ELIMINATED by castration, as discussed above (Krawiec 1994).

3. Dogs won’t be happy after they’re altered.

Dogs are not like humans. They don’t look forward to having children, they don’t expect to raise children and worry over them for 18 years or so, they don’t dream of being grandparents some day. Male dogs don’t even realize that pups they produce are their own offspring. A dog’s reproductive urges are based solely on i
ts hormones. Once the hormones are removed, the urges go away and the dog doesn’t miss them.

4. A bitch will become aggressive after being spayed.

This is rarely true. As mentioned above under “points against sterilization”, a bitch which is ALREADY aggressive may become more aggressive after being spayed. But the vast majority of dogs — those who are NOT already aggressive — will not become aggressive simply because they have been altered.

5. Dogs who are sterilized when young will be less stable and tend to have more behavioral problems than dogs who are left intact.

There is no substantial evidence to support this myth. Dogs who are altered early in life may sometimes be more active than their intact counterparts, but it appears that there is no other significant behavioral difference between dogs neutered very young (7 weeks) and those neutered later (7 months) (Salmeri 1991a). However, it has been well known for many years that altering dogs actually helps to decrease several significant behavioral problems, as mentioned above under “points for sterilization”.

Also, consider this: Service dogs, such as seeing-eye dogs, are almost always altered before being put into service. Many dogs participating in advanced obedience competitions are also sterilized. Obviously, dogs must be very mature and stable in order to fill these jobs, and the surgery is performed because it actually INCREASES their stability by removing the distractions of the sexual cycles.

6. Behavior problems can be prevented by good training and socialization, so sterilization isn’t necessary.

Good training and socialization are definitely essential to having a healthy happy companion. However, even the best-trained dogs in the world can have behavior problems. Remember, the sex hormones act on behavior at a very fundamental level, so those effects may override even the best training. Because of the effects of sex hormones, especially testosterone, intact male dogs are at the highest risk of any dogs for developing aggression problems (Beaver 1983, Blackshaw 1991, Galac 1997, Line 1986, etc ).

7. If I castrate my male dog he won’t protect me any more.

Castrated dogs may actually be more protective, because they will no longer be distracted by the temptations of breeding. Instead of roaming after dogs in heat, or fighting with other males, he will be paying attention to you and you alone. In fact, one recent study has found that castration has NO effect on aggression towards unfamiliar people (Neilson 1997).

8. Only the dominant wolves in a pack get to mate, so intact dogs in a household won’t be frustrated if they don’t get to mate.

What do adolescent wolves do? They either leave the pack, start a pack of their own, challenge the dominant pack members for dominance, or help the parents to raise their future siblings. Do we want our pets to leave or to challenge us? Are we going to breed more puppies just so our intact dogs can have relatives to help raise? No. We want our pet dogs to enjoy living with us, not try to establish dominance over us.

Also, remember that our domestic dogs ARE NOT WOLVES. They act very differently than wolves do in many important ways, so we can’t count on wolves to tell us how our dogs will behave.

9. My dog would make really great puppies/I want to have another dog just like my dog, so I’m going to breed him/her.

Roughly 25-30% of all dogs in shelters are purebreds. Even if your dog is AKC registered, that doesn’t mean that the dog should be bred. Before ANY dog is bred the owner should prove that the dog will actually improve the breed. Thorough health testing, including tests for genetic diseases, should also be performed.

Also, your dog is a unique individual. There is no guarantee that puppies will resemble their parents in looks or personality, especially if the parents are mixed breed dogs.

10. Breeding dogs is a good way to make money.

The only people who make any money from breeding dogs are those who don’t care about the health of their dogs or the quality of the puppies they produce. Responsible breeding requires health testing and medical care, as well as careful consideration of the pedigrees of the parents, their temperament, and whether their puppies would actually improve their breed or merely be more fodder for the shelters.

Medical costs before breeding will include extensive health testing, which may include xrays, blood work, tests for infectious diseases like brucellosis, tests for genetic diseases like von Willebrands, ultrasound exams to check for heart problems, CERF and BAER exams to check for eye and ear problems, and other additional tests depending on the breed of the dog. Medical costs after breeding will include pregnancy tests, ultrasound to check the progress of puppies, perhaps caesarian section if the dog has trouble giving birth, vaccinations, worming, tail docking and ear cropping in cropped or docked breeds, and veterinary care if the puppies should become ill. And that doesn’t even consider stud fees, registration fees, travel costs to get to a stud, expenses to show your dog and prove that it’s worthy of breeding, or the time you must invest in the mating, pregnancy care, whelping, feeding and cleaning the puppies, visits to the veterinary hospital, or advertising and selling the puppies.

11. My children should see the miracle of birth.

First, dogs usually give birth in the middle of the night when the children aren’t going to be around, and dogs prefer to have quiet and privacy during birth. If the mother dog is disturbed by children or too many other witnesses, she may become stressed and abandon the puppies or even kill them. And, of course, there are already too many puppies dying in shelters every day.

Second, if you want your children to learn responsibility through caring for a puppy, there are many great puppies waiting for adoption at your local shelter. If you want to see the miracle of birth, you should first witness the miracle of death by volunteering at your local shelter for a few weeks. And there’s a better alternative: if you want to witness the miracle of birth, rent a video.

12. We can find good homes for the puppies.

For every puppy you breed and place in a new home, a puppy or dog in a shelter may die because it wasn’t adopted. There simply aren’t enough homes for them all. And even if we ignore the puppies in the shelters — are you SURE your puppies are going to good homes? Are you following them in their new homes throughout their lives? Are you willing to take the puppies back if their new homes don’t work out? If you produce a puppy, you are responsible for it throughout its entire life.

13. We should leave our dogs as Nature intended them.

There is nothing “natural” about today’s domesticated dogs. They have been created by many generations of human breeding. We have brought pet dogs into our homes, and we are responsible for their well-being. Dogs benefit in many ways from being sterilized, and suffer few serious consequences.

ISSUES OF SPECIAL IMPORTANCE FOR DOBERMANS

{jb_blackdisc}1.{/jb_blackdisc} Dobermans as a breed tend to be dominant, forceful, determined dogs, and they are large and powerful.

Therefore, it can be especially difficult to handle intact male OR female dobermans, especially if there is more than one dog in the house. Because of
these breed tendencies, sterilizing your doberman can be especially important in helping you to live with your dog.

{jb_blackdisc}2.{/jb_blackdisc} Dobermans are especially susceptible to prostatic diseases.

In fact, doberman pinschers appear to be the MOST common breed to suffer from prostatic disease (Krawiec 1992), which makes castration even MORE important for our breed.

{jb_blackdisc}3.{/jb_blackdisc} Dobermans are more likely than most other breeds to have problems with urinary incontinence.

This is true, whether the incontinence is related to sterilization (Arnold 1997, Holt 1993) or not (Adams 1983). Fortunately, most incontinent dobermans respond very well to the drug phenylpropanolamine.

{jb_blackdisc}4.{/jb_blackdisc} Dobermans are especially susceptible to hypothyroidism.

Fortunately, hypothyroidism is easily treated with thyroid supplements.

{jb_blackdisc}5.{/jb_blackdisc} Dobermans may have a bleeding disorder which makes surgery more risky than normal.

Some dobermans suffer from the disorder known as von Willebrand´s disease (vWD). This disease can prevent normal blood clotting, and may lead to life-threatening blood loss (Brooks 1992, Meyers 1992, Thomas 1996). Fortunately, it is not common for dobermans to have problems with bleeding during surgeries even if they do have the vWD trait. For maximum safety, it is best to test for vWD before surgery is performed, either through genetic testing or clotting tests. Your vet will have more information on these tests.

REFERENCES

• Aaron, A., K. Eggleton, C. Power, P. E. Holt. (1996). Urethral sphincter mechanism incompetence in male dogs: a retrospective analysis of 54 cases. Veterinary Record , 139(22): 542-546.

• Adams, W. M., & DiBartola, S. P. (1983). Radiographic and clinical features of pelvic bladder in the dog. Journal of the American Veterinary Medical Association, 182(11): 1212-1217.

• Albanese, F., & Galeotti, F. (1997). Alopecia responding to castration in two Pomeranians. Veterinaria Cremona, No. supl.2: 19-22.

• Arnold S. (1997). Urinary incontinence in castrated bitches. Part 1: Significance, clinical aspects and etiopathogenesis. Schweizer Archiv fur Tierheilkunde, 1997;139(6): 271-276.

• Arnold, S. (1997). Urinary incontinence in spayed bitches. Part 2. Diagnosis and treatment. Schweizer Archiv fur Tierheilkunde, 139(7): 319-324.

• Arnold, S., Arnold, P., Hubler, M., Casal, M., & Rusch, P. (1989). Urinary incontinence in spayed bitches: frequency and breed predisposition. Schweizer Archiv fur Tierheilkunde, 131(5): 259-263.

• Askew, H. R. (1992). Effect of castration on behaviour problems in dogs. Kleintierpraxis, 37(12): 863-864.

• Bastianello, S. S. (1983). A survey on neoplasia in domestic species over a 40-year period from 1935 to 1974 in the Republic of South Africa. VI. Tumours occurring in dogs. Onderstepoort Journal of Veterinary Research, 50(3), 199-220.

• Beaver, B. V. (1983). Clinical classification of canine aggression. Applied Animal Ethology, 10(1-sup-2): 35-43.

• Bell, F. W., Klausner, J. S., Hayden, D. W., Feeney, D. A., & Johnston, S. D. (1991). Clinical and pathologic features of prostatic adenocarcinoma in sexually intact and castrated dogs: 31 cases (1970-1987). Journal of the American Veterinary Medical Association, 199(11): 1623-1630.

• Bessonov, A. S., Shalmenov, M. S., Prokopic, J., & Sterba, J. (1986). Castration of dogs as a preventive measure against echinococcosis. Proceedings of the second International Symposium on taeniasis cysticercosis and echinococcosis hydatidosis 2 7 December 1985, Czechoslovakia. 1986: 224-230.

• Blackshaw, J. K. (1991). An overview of types of aggressive behaviour in dogs and methods of treatment. Applied Animal Behaviour Science, 30(3-4): 351-361.

• Bronson, R. T. (1981). Age at death of necropsied intact and neutered cats. American Journal of Veterinary Research, 42(9): 1606-1608.

• Brooks, M. (1992). Management of canine von Willebrand’s disease. Problems in Veterinary Medicine, 4(4): 636-646.

• Coggins, J. R. Effect of season, sex, and age on prevalence of parasitism in dogs from southeastern Wisconsin. Journal of the Helminthological Society of Washington, 65(2): 219-224.

• Combemale, P. (1929). Sur la psychophysiologie du chien prive de testicules. / On the psychophysiology of the castrated dog. Comptes Rendus des Seances. Societe de Biologie Paris, 101: 1133-1135.

• Cowan, L. A., Barsanti, J. A., Crowell, W., & Brown, J. (1991). Effects of castration on chronic bacterial prostatitis in dogs. Journal of the American Veterinary Medical Association, 199(3): 346-350.

• Crenshaw, W. E., & Carter, C. N. (1995). Should dogs in animal shelters be neutered early? Veterinary Medicine, 90(8): 756, 758-760.

• Crowell-Davis, S. L. (1991). Identifying and correcting human-directed dominance aggression of dogs. Veterinary Medicine, 86(10): 990-998.

• Dorn, A., Bone, D., & Bellah, J. (1985). Sex hormone-related diseases treated surgically in male dogs. Modern Veterinary Practice, 66: 727-733.

• Fagella, A.M. & Aronsohn, M.G. (1994). Evaluation of anesthetic protocols for neutering 6-to-14-week-old pups. Journal of the American Veterinary Medical Association, 205(2): 308-314.

• Fettman, M. J., Stanton, C. A., Banks, L. L., Hamar, D. W., Johnson, D. E., Hegstad, R. L., & Johnston, S. (1997). Effects of neutering on bodyweight, metabolic rate and glucose tolerance of domestic cats. Research in Veterinary Science, 62(2): 131-136.

• Flynn, M. F., Hardie, E. M., & Armstrong, P. J. (1996). Effect of ovariohysterectomy on maintenance energy requirement in cats. Journal of the American Veterinary Medical Association, 209(9): 1572-1581.

• Fry, P. D. (1987). Antisocial behaviour in the dog. The effects of castration. Veterinary Practice, 19(17): 4-5, 7.

• Galac, S., & Knol, B. W. (1997). Fear-motivated aggression in dogs: patient characteristics, diagnosis and therapy. Animal Welfare, 6(1): 9-15.

• Gregory S.P. (1994). Developments in the understanding of the pathophysiology of urethral sphincter mechanism in competence in the bitch. British Veterinary Journal, 150(2): 135-150.

• Hart, B. L. (1976). Behavioral effects of castration. Canine Practice, 3(3): 10-21.

• Heider, H. J. (1990). Castration – therapeutic indications. Kleintierprax is, 35(12): 644-650.

• Heidenberger, E., & Unshelm, J. (1990). Changes of behaviour in dogs after castration. Tierarztliche Praxis, 13(1): 69-75.

• Heughebaert, A., Cock, I. d., Schepper, J. d., De Cock, I., & De Schepper, J. (1988). Urinary incontinence in spayed bitches and its treatment with phenylpropanolamine. Vlaams Diergeneeskun
  dig Tijdschrift, 57(1): 27-31.

• Holt P. E, & Thrusfield, M. V. (1993). Association in bitches between breed, size, neutering and docking, and acquired urinary incontinence due to incompetence of the urethral sphincter mechanism. Veterinary Record , 133(8): 177-180.

• Hopkins, S. G., Schubert, T. A., & Hart, B. L. (1976). Castration of adult male dogs: effects on roaming, aggression, urine marking, and mounting. Journal of the American Veterinary Medical Association, 168(12): 1108-1110.

• Houston, D. M., Ribble, C. S., & Head, L. L. (1992). Risk factors associated with parvovirus enteritis in dogs: 283 cases (1982-1991). Journal of the American Veterinary Medical Association, 208(4): 542-546.

• Howe, L. M. (1997). Short-term results and complications of prepubertal gonadectomy in cats and dogs. Journal of the American Veterinary Medical Association, 211(1): 57-62.

• Jagoe, J. A., & Serpell, J. A. (1988). Optimum time for neutering. Veterinary Record, 122(18): 447.

• Knol, B. W., & Egberink Alink, S. T. (1989). Treatment of problem behaviour in dogs and cats by castration and progestagen administration: a review. Veterinary Quarterly, 11(2): 102-107.

• Koltveit, A. J. (1991). Pet overpopulation. Journal of the American Veterinary Medical Association, 198(7): 1151-1243.

• Kraft, W., & Danckert, D. (1996). Lifespan of a cat population [in Germany]. Kleintierpraxis, 42(1): 21-28.

• Krawiec, D. R. (1994). Canine prostate disease. Journal of the American Veterinary Medical Association, 204(10): 1561-1564.

• Krawiec, D. R., & Heflin, D. (1992). Study of prostatic disease in dogs: 177 cases (1981-1986). Journal of the American Veterinary Medical Association, 200(8): 1119-1122.

• Kunz, E., & Rensing, H. Castration-responsive alopecia in a male Samoyed. Kleintierpraxis, 42(11): 921-924.

• Kusch, S. (1985). Incidence of malignant neoplasia in dogs based on PM statistics of the Institute of Animal Pathology, Munich, 1970-1984.

• Lieberman, L.L. (1987). A case for neutering pups and kittens at two months of age. Journal of the American Veterinary Medical Association, 191: 518-521.

• Line, S., & Voith, V. L. (1986). Dominance aggression of dogs toward people: Behavior profile and response to treatment. Applied Animal Behaviour Science, 16(1): 77-83.

• Maarschalkerweerd, R. J., Endenburg, N., Kirpensteijn, J., & Knol, B. W. Influence of orchiectomy on canine behaviour. Veterinary Record, 140(24): 617-619.

• The Merck Veterinary Manual, 1991,7th ed, Merck and Co., Inc, Rahway.

• Meyers, K. M., Wardrop, K. J., & Meinkoth, J. (1992). Canine von Willebrand’s disease: pathobiology, diagnsosis, and short-term treatment. Compendium on Continuing Education for the Practicing Veterinarian, 14(1): 13-22.

• National Council on Pet Population Study and Policy, National Shelter Census: 1994 results. Fort Collins, CO.

• Neilson, J. C., Eckstein, R. A., & Hart, B. L. (1997).Effect of castration on problem behaviors in male dogs with reference to age and duration of behavior. Journal of the American Veterinary Medical Association, 211(2): 180-182.

• O’ Farrell, V., & Peachey, E. (1990). Behavioural effects of ovariohysterectomy on bitches. Journal of Small Animal Practice, 31(12): 595-598.

• Obradovich, J., Walshaw, R., & Goullaud, E. (1987). The influence of castration on the development of prostatic carcinoma in the dog. 43 cases (1978-1985). Journal of Veterinary Internal Medicine, 1(4): 183-187.

• Olsen, P. N., Moulton, C., Nett, T., & al, e. (1991). Pet overpopulation: a challenge for companion animal veterinarians in the 1990s. Journal of the American Veterinary Medical Association, 198(7): 1151-1152.

• Panciera D.L. (1994). Hypothyroidism in dogs: 66 cases (1987-1992). Journal of the American Veterinary Medical Association, 204(5): 761-767.

• Pollari, F. L., & Bonnett, B. N. (1995). Evaluation of postoperative complication s following elective surgeries of dogs and cats at private practices using computer records. Canadian Veterinary Journal, 37(11): 672-678.

• Pollari, F. L., Bonnett, B. N., Bamsey, S. C., Meek, A. H., & Allen, D. G (1996). Postoperative complications of elective surgeries in dogs and cats determined by examining electronic and paper medical records. Journal of the American Veterinary Medical Association, 208(11), 1882-1886.

• Root, M. V. (1995). Early spay-neuter in the cat: effect on development of obesity and metabolic rate. Veterinary Clinical Nutrition, 2(4), 132-134.

• Salmeri, K. R., Bloomberg, M. S., Scruggs, S. L., & Shille, V. (1991a). Gonadectomy in immature dogs: effects on skeletal, physical, and behavioral development. Journal of the American Veterinary Medical Association, 198(7): 1193-1203.

• Salmeri, K.R., Olsen, P.N., & Bloomberg, M.S. (1991b). Elective gonadectomy in dogs: a review. Journal of the American Veterinary Medicine Association, 198(7): 1183-1191.

• Schneinder, R., Dorn, C.R., & Taylor, D. (1969). Factors influencing canine mammary cancer development and post-surgical survival rates. Journal of the National Institutes of Cancer, 45: 1249-1251.

• Schneinder, R. (1970). Comparison of age, sex and incidence rates in humans and canine breast cancer. Cancer, 26: 419-426.

• Shal’ menov, M. S. (1984). Castration of dogs as a method of controlling echinococcosis. Byulleten’ Vsesoyuznogo Instituta Gel’mintologii im. K.I. Skryabina, No.39: 40-44.

• Thomas, J. S. (1996). Von Willebrand’s disease in the dog and cat. Veterinary Clinics of North America, Small Animal Practice, 26(5): 1089-1110.

• Thrusfield, M. V., Holt, P. E., & Muirhead, R. H. (1993). Acquired urinary incontinence in bitches: its incidence and relationship to neutering practices. Journal of Small Animal Practice, 39(12): 559-566.