Canine reproduction

A dog's glans consists of two sections: Behind the lower, long part (pars longa glandis) lies the "knot" (Bulbus glandis)[1] which expands only after penetrating the vagina and causes the male dog to remain inside the bitch ("Tie") for some time after ejaculation (typically between 15 and 30 min).

The shaft of a dogs penis is not visible, even during an erection; however its pathway can be felt starting at the knot passing between the hind legs and carrying on up to the anus.

The urethra is located inside of a downward facing groove on the baculum and ends at the tip of the penis (urethral process).

Initial changes include swelling of the vulva lips, which become pliable, small amounts of bloody vaginal discharge, frequent urination, and signs of restlessness.

Estrus follows, in which estrogen levels are high, mature eggs are released from both ovaries, and females become receptive both physically and mentally to copulation.

At that time she may gain weight, have mammary gland development, produce milk, and exhibit nesting behaviours.

[5] As with most tetrapods, canine copulation involves the male mounting the female from behind, a position that is colloquially referred to as "doggy style" but does not have a specifically known origin.

[10] It is during this time that the male's penis expands and it is important that the bulbus gland is sufficiently far inside for the female to be able to trap it.

Male canines are the only animals that have a locking bulbus glandis or "bulb", a spherical area of erectile tissue at the base of the penis.

[11] During copulation, and only after the male's penis is fully inside the female's vagina, the bulbus glandis becomes engorged with blood.

While characteristic of mating in most canids, the copulatory tie has been reported to be absent[13] or very brief (less than one minute)[14] in the African wild dog, possibly due to the abundance of large predators in its environment.

[15] When the penis is locked into the vagina by the bulbus glandis (when the stud is "tied"), thrusting behavior stops and the male will usually lift a leg and swing it over the female's back while turning around.

[24] 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.

[citation needed] A female dog usually has 10 teats, though this does not mean she can necessarily provide sufficient nutrition for 10 puppies in one litter.

[citation needed] An average litter consists of about five to six puppies, though this number may vary widely based on the breed of dog.

[citation needed] A large scale study in Norway showed that across all breeds, about 4% of pups will be stillborn and a further 4% will die within the first week (early neonatal mortality).

[27] Common causes of early neonatal mortality are bacteria infection, fetal asphyxia and fading puppy syndrome.

[28] Inbreeding depression is a reduction in progeny fitness due largely to the homozygous expression of deleterious recessive mutations.

[29] The gray wolves (Canis lupus) of Isle Royale National Park, Michigan, US, were a small highly inbred population that was considered to be at the threshold of extinction in 2019.

[30] This wolf population had been experiencing severe inbreeding depression largely due to the homozygous expression of strongly deleterious recessive mutations.

[30][31] Another highly inbred Scandinavian population of wolves (Canis lupus) also suffered from inbreeding depression that was again attributed to the homozygous expression of deleterious recessive mutations.

Inbreeding avoidance via mate selection is characteristic of the species and has important potential consequences for population persistence.

Red wolves primarily live in packs composed of a socially monogamous breeding pair and offspring of different ages.

Using long-term data on red wolf individuals of known pedigree, it was found that inbreeding among first-degree relatives was rare.

The union of two unrelated individuals in a new home range is the predominant pattern of breeding pair formation.

[29] Cross-fertilization between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.

Signs and symptoms include fever, lethargy, loss of appetite, excessive thirst, restlessness, a foul smelling vaginal discharge which may or may not be bloody, infertility, or they may be asymptomatic.

An artificial vagina is prepared, which is a conical thin latex sleeve ending in a sterile collection tube.

[46] 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.

[citation needed] Female cats and dogs are seven times more likely to develop mammary tumors if they are not spayed before their first heat cycle.