Canine reproduction

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This article focusses 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.

Contents 1 Canine sexual anatomy and development 1.1 General 1.2 Males 1.3 Females 2 The reproductive cycle 2.1 Female cycle 3 Copulation 4 Gestation and litters 5 Clinical issues 6 Dog breeding 6.1 Timing 6.2 Procedure 6.3 Amateur breeding 6.4 Professional breeding 7 Spaying and neutering 8 Variations for other types of canid 9 Glossary of terms 10 References 11 See also

[edit] Canine sexual anatomy and development

Main article: Animal sexuality

See below for a glossary of terms used in this article.

[edit] General

In domestic dogs, sexual maturity (puberty) begins to happen around age 6 to 12 months for both males and females, although this can be delayed until up to two years old for some large breeds. Adolescence for most domestic dogs is around 12 to 15 months, beyond which they are for the most part more adult than puppy. 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.

[edit] Males

[edit] Females

Females have a twice-yearly fertile period, known as 'seasons', during which her body prepares for pregnancy, and at the peak she will come "into heat", her fertile period, during which time she will be mentally and physically receptive to copulation. A female is able to become pregnant on her first heat; this is not normally considered advisable as she is mentally and physically still young in other ways.

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 different dogs, but a particular dog's cycle tends to be consistent through her life. This is also called in season or in heat. 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. The different rates of maturation are responsible for the menarche, not the chronological age. They then experience fertile seasons biannually until old age. Female dogs do not experience menopause, although their cycles will become irregular and fertility becomes unpredictable as the become older. Dogs over around 7 or 8 years are usually considered no longer appropriate for breeding, but can still remain fertile.

[edit] The reproductive cycle

[edit] Female cycle

[edit] Copulation

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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 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, 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' websites 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.

[edit] 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 12 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 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.

[edit] Clinical issues

[edit] Dog breeding

[edit] 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.

[edit] Procedure

[edit] Amateur breeding

[edit] Professional breeding

Among professional breeders, dogs are only allowed to mate for a specific purpose. Sometimes dogs are bred to create puppies to sell, or sometimes to carry on an award-winning purebred line. Breeders who do this are usually experienced in this process. Dog breeders have access to records which allow them to accurately guess which characteristics will "breed true" in a particular dog. Dog breeders also have accurate information on the complexities of the reproductive process for the breed of dog that they are accustomed to handling.

[edit] Spaying and neutering

Main article: Spaying and neutering

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Spaying (females only) and neutering (both genders but more usually 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. Neutering has also been known to reduce aggression in male dogs, but can occasionally increase aggression in female dogs.^{[citation needed]}

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. In the less developed countries of Europe, spaying or neutering of dogs is less common, and owners are usually instead advised to keep their dogs on leash and under supervision to avoid unwanted matings; drugs are used to prevent pregnancy and abort unwanted litters.^{[citation needed]}

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 neutering can also decrease the risk of hormone-driven diseases such as mammary cancer, as well as undesired hormone-driven behaviors. The hormonal changes involved with sterilization are likely to somewhat change the animal's personality, however, and some object to spaying and neutering as the sterilization could be carried out without the excision of organs.

Contrary to myth, it is not required 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; these myths are responsible for numerous unnecessary health problems and unwanted puppies.^{[citation needed]} Female dogs spayed before their first heat have a vastly lower incidence of mammary tumors than dogs which are spayed after their first heat or pregnancy (1% verses 22%).^{[citation needed]} A female dog can become pregnant on her first heat cycle (which can take place as early as six months), and should be kept away from intact male dogs, including littermates, over the age of 4 months.^{[citation needed]}

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.^{[citation needed]}

[edit] Variations for other types of canid

[edit] Glossary of terms

Main article: Glossary of terms used in animal husbandry

[edit] References

• Siegal, Mordecai (1995). in (editor): UCDavis Book of Dogs. HarperCollins. ISBN 0-06-270136-3. 

[edit] See also

• Canidae
• Puppy
• Animal husbandry