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Canine reproduction



This article focuses upon reproduction of domestic dogs. Reproduction within other types of canid is not covered at present.

 

This article covers the process of reproduction in canines (dogs and their relatives), as well as related veterinary and breeding information.

Additional recommended knowledge

Contents

Canine sexual anatomy and development

Main article: Animal sexuality
See below for a glossary of terms used in this article.

General

The female sex of the domestic canine is referred to as a bitch, and the male of the same species is referred to as a dog. In domestic canines, sexual maturity (puberty) occurs between the ages of 6 to 12 months for both males and females, although this can be delayed until up to two years of age for some large breeds. Pregnancy is possible as soon as the first estrus cycle, but breeding is not recommended prior to the second cycle. As with other domesticated species, domestication has selectively bred for higher libido and earlier and more frequent breeding cycles in dogs than in their wild ancestors.

Studs

Like most males of any species, the development of secondary sexual characteristics is dependent on the production of testosterone by the testes. Secondary sex characteristics include increased muscle mass, penile enlargement, anal hypertrophy, and development of a gland at the base of the tail. Testosterone levels are also responsible for the sex drive, which is not cyclical. Studs are receptive to mating at any time, and are willing to mate even if the bitch is not fertile. The dog's penis has a bone, called the os penis, which provides rigidity regardless of level of sexual stimulation. The remainder of the anatomy is similar to other species. Studs have a prostate gland and are susceptible to similar problems as humans.

Bitches

The anatomy of the bitch is similar to other mammals. They have two ovaries located caudal to the kidneys in the abdominal cavity. They have a bicornuate uterus, and there is single uterine body which is sealed off by the cervix. The cervix is muscular with fibrous tissue support, and closes in a stellate pattern. The vaginal vault extends to the opening of the urethra in the dorsal wall, at which point it is termed the vestibule. The vestibule makes a steep downward turn and the exit of the reproductive tract is the vulva. Bitches have a clitoris just inside the vulva. Bitches often have a vaginal stricture, which is a remnant of where the vagina and vestibule fused together during embryonic development. This stricture is often asymptomatic and is broken down during mating.

As with most domesticated species, one of the first and strongest effects seen from selective breeding is selection for cooperation with the breeding process as directed by humans. In domestic dogs, one of the behaviours that is noted is the abolition of the pair bond seen in wild canines. The ability of female domestic dog to come into estrus at any time of the year and usually twice a year is also valued. The amount of time between cycles varies greatly among individual dogs, but a particular dog's cycle tends to be consistent through her life. Conversely, undomesticated canine species experience estrus once a year, typically in late winter.

Most female dogs come into season for the first time between 6 and 12 months, although some larger breeds delay until as late as 2 years. Like most mammals, the age that a bitch first comes into season is mostly a function of her current body weight as a proportion of her body weight when fully mature. They then experience estrus about every seven months until old age. Female dogs do not experience menopause, although their cycles will become irregular and fertility becomes unpredictable as they become older. Dogs over around 7 or 8 years are usually considered no longer appropriate for breeding, but can still remain fertile.

The reproductive cycle

Female cycle

The average length of the reproductive cycle for bitches is 7 months. Bitches reach sexual maturity (puberty) between 4 to 18 months of age. There is a tremendous variability in the maturation age between breeds, and even within a breed of dog. The first stage of the reproductive cycle is proestrus, in which eggs in the ovaries begin to mature and estrogen levels begin to rise. During this stage males are attracted to non-receptive females. Initially, the vulvar lips will swell up and become pliables, there are small amounts of bloody vaginal discharge, and signs of frequent urination and restlessness. Proestrus generally last 9 days. Estrus is the next stage, in which estrogen levels are high, mature eggs are released from the ovaries, and the bitch mentally and physically becomes receptive to copulation. It is only during estrus that copulation will result in pregnancy. During proestrus and estrus, bitches may have a clear to bloody discharge. This stage is also known as "heat." The length of these cycles varies greatly between individuals. Proestrus and estrus can last anywhere from 5 days to 21 days. Diestrus is the period following mating. Diestrus lasts approximately 56 to 58 days in the pregnant bitch, and 60 to 100 days in the non-pregnant bitch. During both of these periods, progesterone levels are high. Because the hormonal profile of a pregnant bitch and a bitch in diestrus are the same, sometimes a non-pregnant bitch will go through a period of pseudo-pregnancy. At that time she may gain weight, have mammary gland development, produce milk, and exhibit nesting behaviours. Anestrus is the period of reproductive quiescence. The bitch has no attraction to or from the male. Anestrus generally lasts four to five months.

Copulation

When copulating, a male canine initially mounts the female from behind, as with most tetrapods, a position known informally as doggy style. The female will hold her tail to the side (called "flagging") and allow this if receptive. If unreceptive she may sit or lie down, snap, move away, or otherwise be uncooperative or not allow mating. The male will often move about as he tries to get a good purchase upon her, and whilst attempting penetration of his penis to the female's vulva. At this point, the penis is not erect, it is slender and held rigid by a small bone inside, known as the baculum.

When the male achieves penetration, he will often hold tighter and thrust faster, and it is at this point when he is mating that the male's penis expands. Canine reproduction is different from human sexual intercourse, because human males become erect first, and then enter the female; canine males enter first, then swell and become erect.

The male dog has a bulbus glandis, a spherical area of erectile tissue at the base of the penis, which traps the penis inside the female's vagina during copulation as it becomes engorged with blood. [1]

Once the penis is locked into the vagina by the bulbus glandis (when the stud is "tied"), the male will usually lift a leg and swing it over the female's back while turning around. The two stand with their hind ends touching and the penis locked inside the vagina while ejaculation occurs, decreasing leakage of semen from the vagina. After some time, typically 5 - 20 minutes (but sometimes longer), the bulbus glandis disengorges, allowing the mates to separate. Virgin dogs can become quite distressed at finding themselves unable to separate during their first copulation, and may try to pull away or run. Dog breeders often suggest it is appropriate for those involved to help calm and settle the mating dogs once this stage is reached, if they show anxiety, through until eventual separation.

Note that similar canine mounting behavior (sometimes with pelvic thrusting) is also used by dominant canines of both sexes. Dominance mounting, with or without thrusting, should not be confused with copulatory mounting, in which the thrusting is short term until a "tie" is achieved.

Gestation and litters

   Dogs bear their litters roughly 9 weeks after fertilization, although the length of gestation can vary from 56 to 72 days.

A general rule of thumb is that a mammal will produce half as many offspring as the number of teats on the mother. This rule is altered in domesticated animals since larger litters are often favoured for economic reasons and in dogs, particularly, the great range of sizes and shapes plays a role in how many healthy puppies a female can carry. An average litter consists of about six puppies, though this number may vary widely based on the breed of dog. Toy dogs generally produce from one to four puppies in each litter, while much larger breeds may average as many as 14 pups in each litter. The number of puppies also varies with the mother's age and health, the father's sperm count, the timing of the breeding, and many other factors.

Some veterinarians say that mating a stud and bitch every other day is the way to a full litter. Others will say that mating every day is much better; it reduces the chance of having one puppy being born prematurely or much later than the other pups of the litter.

Some breeds have been developed to emphasize certain physical traits beyond the point at which they can safely bear litters on their own. For example, the Bulldog often requires artificial insemination and almost always requires cesarean section for giving birth.

Since a mother can provide nutrients and care to only a limited number of offspring, humans must assist in the care and feeding when the litter exceeds approximately eight puppies.

Clinical issues

Owners of intact bitches should be aware of pyometra, an acute infection similar in effect to appendicitis which can affect any intact bitch, and which is always very serious and often fatal. The period after heat, when the cervix is closing, is a high risk period for this disease and close attention should be paid for any signs of fever, lethargy, loss of appetite, excessive thirst, or any other indicators of sickness. Pyometra should be treated as a medical emergency if suspected. Contrary to myth, pyometra can strike any intact bitch, whether she has been bred or not, and whether it is her first or tenth season, although it is more common as dogs become older.

Dog breeding

Timing

Breeders and veterinarians have various methods for determining the best time to breed a bitch. Breeders rely on both the visible signs of estrus and modern testing methods when they are trying to decide the best time to breed. Visible signs of estrus (or heat) include vaginal bleeding, vulvar swelling and the female dog responding to a male dog by standing and "freezing" to allow the male dog to mount her. The three most commonly used medical methods for determining estrus are: Blood Progesterone, Blood Luetinizing Hormone(LH), and a Vaginal Smear. The first two test for the level of those hormones in the blood, and a “smear” checks the amount of cornified epithelial cells present in the vaginal secretions.

Many breeders prefer the LH and Progesterone tests because they are highly accurate while the smear method can be unreliable (especially when done by a vet who has limited experience performing this test). However the smear method is still widely used because it is much cheaper, and it's less stressful for the bitch because no blood has to be drawn.

Before the advent of modern testing a breeder might mate the two dogs every two to three days during the bitch's estrus to ensure that fertilization had occurred. Today, most breeders will track a bitch's cycle (usually by Progesterone blood tests) and breed her only during a 3 day window when she is most fertile and most receptive to the male.

 A female dog allowed to roam freely during estrus can end up producing puppies from multiple fathers. Breeders might occasionally breed a female to more than one desirable male for various reasons, in which case the only reliable way to determine parentage of the puppies is through DNA testing of the pups.

Procedure

Natural breeding can be easily accomplished between most dogs as long as the bitch is in estrus during the attempt. Simply placing both dogs in the same environment for a few days will usually result in a pregnancy.

If, due to breed characteristics or the stud only being available for a short time, natural breeding is not desirable, artificial insemination can be used. This is often done at a veterinarian's office. An artificial vagina is prepared, which is a conical thin latex sleeve ending in a sterile collection tube. The inside of the latex sleeve is lightly lubricated. The male is allowed to sniff a female in estrus. Experienced studs cooperate readily in the process. New studs often require encouragement in the form of manual stimulation. Generally the male will mount the female, and the collector quickly directs his penis into the latex sleeve. The male emits semen in the normal way and it is collected in the tube. The semen is then drawn up into a long thin pipette. The pipette is threaded through the bitch's cervix and the semen deposited in her uterus. There is ongoing research into techniques for chilling or freezing canine semen. Currently, for high quality breedings, one of the mates is often flown to the location of the other for this procedure.

Amateur breeding

Amateur breeding is also referred to as "backyard breeding." People practice this for a variety of reasons - they may want their dog to experience pregnancy, they may have failed to spay their dog, or they plan on selling the offspring. Due to the huge numbers of unwanted dogs that are routinely euthanized in animal shelters, this type of breeding is not always agreed with.

Purebred dog breeding arose in response to jobs for which a specific type of dog was needed, whether hunting, guarding, herding, or other work. Different qualities are needed for these various jobs, such as a soft mouth for retrievers or a herding instinct for sheep dogs. In order to fix the genetic breed features so that two dogs of the same breed could reproduce themselves, all breeds have historically started with inbreeding. Those fixed qualities are today referred to as the breed standard. Standards are set and approved by each national breed club, and adopted by the American Kennel Club. Many standards are quite specific and not open to interpretation, such as height, ear type (prick versus drop), tail, coat, and other conformation features. Other aspects of each breed may be open to interpretation. Breeders may focus on conformation, temperament, or working qualities, such as hunting, pointing, herding, or rescue.

Professional breeders are not only aware of their breed standards, but attempt to improve their own line by either linebreeding or by introducing new lines. Linebreeding or inbreeding in itself does not cause birth defects or other genetic health conditions, as is commonly thought. While inbreeding can affect some reproductive traits or decrease size slightly, other genetic defects occur only if the genes are present for these anomalies. This is true whether or not the breeding pair are related; in other words, two dogs mated with hip dysplasia will likely result in dysplastic offspring, whether or not the dam and sire were related or even of the same breed. Professional breeders who adhere to their national breed club guidelines also generally test for genetic defects prior to breeding; some examples include testing for hip dysplasia, various eye conditions, thyroid problems, and epilepsy. There are national registries for many of these genetic tests. Rarely do "backyard breeders" perform these tests. Any purebred breeding should be undertaken with knowledge of the breed standard, testing for genetic-based disorders, and some knowledge of genetics.

Spaying and neutering

Main article: Spaying and neutering

Spaying (females) and castrating (males) refers to the sterilization of animals--usually by removal of the male's testicles or the female's ovaries and uterus--in order to eliminate the ability to procreate, and reduce sex drive. Castration has also been known to reduce aggression in male dogs, but spaying has been shown to occasionally increase aggression in female dogs.[1]

Animal control agencies in the United States and the ASPCA advise that dogs not intended for further breeding should be spayed or neutered so that they do not have undesired puppies.[2]

Because of the overpopulation of dogs in some countries, puppies born to strays or as the result of accidental breedings often end up being killed in animal shelters. Spaying and castrating can also decrease the risk of hormone-driven diseases such as mammary cancer, as well as undesired hormone-driven behaviors. However, certain medical problems are more likely after neutering, such as urinary incontinence in females[3] and prostate cancer in males.[4] The hormonal changes involved with sterilization are likely to somewhat change the animal's personality, however, and some object to spaying and castrating as the sterilization could be carried out without the excision of organs.

It is not essential for a female dog to either experience a heat cycle or have puppies before spaying, and likewise, a male dog does not need the experience of mating before neutering.

Female cats and dogs are seven times more likely to develop mammary tumors if they are not spayed before their first heat cycle. [5] The high dietary estrogen content of the average commercial pet food as well as the estrogenic activity of topical pesticides[citation needed] may be contributing factors in the development of mammary cancer, especially when these exogenous sources are added to those normal estrogens produced by the body. Dog food containing soybeans or soybean fractions have been found to contain phytoestrogens in levels that could have biological effects when ingested longterm.[6]

Gender-preservative surgeries such as vasectomy and tubal ligation are possible, but do not appear to be popular due to the continuation of gender-specific behaviors and disease risks.

Variations for other types of canid

Glossary of terms

Main article: Glossary of terms used in animal husbandry

References

  1. ^ Heidenberger E, Unshelm J (1990). "[Changes in the behavior of dogs after castration]" (in German). Tierärztliche Praxis 18 (1): 69-75. PMID 2326799.
  2. ^ Top 10 reasons to spay/neuter your pet. American Society for Prevention of Cruelty to Animals. Retrieved on 2007-05-16.
  3. ^ Arnold S (1997). "[Urinary incontinence in castrated bitches. Part 1: Significance, clinical aspects and etiopathogenesis]" (in German). Schweiz. Arch. Tierheilkd. 139 (6): 271-6. PMID 9411733.
  4. ^ Johnston SD, Kamolpatana K, Root-Kustritz MV, Johnston GR (2000). "Prostatic disorders in the dog". Anim. Reprod. Sci. 60-61: 405-15. PMID 10844211.
  5. ^ Morrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed.). Williams and Wilkins. ISBN 0-683-06105-4. 
  6. ^ Cerundolo R, Court MH, Hao Q, Michel KE (2004). "Identification and concentration of soy phytoestrogens in commercial dog foods". Am. J. Vet. Res. 65 (5): 592-6. PMID 15141878.
  • Siegal, Mordecai (1995). in (editor): UCDavis Book of Dogs. HarperCollins. ISBN 0-06-270136-3. 

See also

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Canine_reproduction". A list of authors is available in Wikipedia.
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