Canine reproduction

Sexual reproduction in canine species

Canine reproduction is the process of sexual reproduction in domestic dogs, wolves, coyotes and other canine species.

As with all mammals, a dog's penis is made up of three pieces of erectile tissue. These are the two corpora cavernosa and the singular corpus spongiosum which continues in the glans. A notable difference from the human penis is that the visible part during an erection consists entirely of the glans. The retractor muscle is attached at the shaft of the penis. It is a paired smooth muscle that is used to retract the penis back into the sheath.

A dog's glans consists of two sections: Behind the lower, long part (pars longa glandis) lies the "knot" (Bulbus glandis) 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 ancestors.

The average length of the reproductive cycle for females is 2–4 weeks. Females reach sexual maturity (puberty) between 8 and 18 months of age. There is a tremendous variability in the maturation age between breeds, and even within a breed of dog. 1. Proestrus, in which eggs in the ovaries begin to mature and estrogen levels begin to rise, is the first stage of the reproductive cycle. During this stage females, though non receptive, attract males. Initial changes include swelling of the vulva lips, which become pliable, small amounts of bloody vaginal discharge, frequent urination, and signs of restlessness. Proestrus generally lasts nine days. If the female is unreceptive, she may sit, lie down, snap, retreat, or otherwise be uncooperative. If the female is receptive, she will stand still and hold her tail to the side, a stance referred to as "flagging". At the time of penetration, the canine penis is not erect, and only able to penetrate the female because it includes a narrow bone called the "baculum", a feature of most placental mammals. When the male achieves penetration, he will usually hold the female tighter and thrust deeply. 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. During copulation, and only after the male's penis is fully inside the female's vagina, the bulbus glandis becomes engorged with blood. When the female's vagina subsequently contracts, the penis becomes locked inside the female. This is known as "tying" or "knotting". While characteristic of mating in most canids, the copulatory tie has been reported to be absent or very brief (less than one minute) in the African wild dog, possibly due to the abundance of large predators in its environment. 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. 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 between 5 and 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 handlers to attempt to calm the mating dogs if they show anxiety once this stage is reached. After mating, the male usually licks his penis and prepuce.

Gestation in a dog is 63 days in length, if measured from the day of ovulation. Since it is difficult to determine the exact date of ovulation, errors are often made in calculating gestation period. Canine sperm can live for 10 to 11 days in the oviducts (fallopian tubes) so if a female is bred 10 days before the oocytes (eggs) can be fertilized, she will appear to have a gestation length of 70 days. If she is bred on the day the oocytes can be fertilized, her gestation length will appear to be 60 days long. During gestation, many physiological changes are similar to other mammals like humans. This results in similar shifts in nutrients in the blood of dogs, especially affecting glucose, fatty acids (like DHA) and amino acid (like BCAA) levels. A 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. A female dog usually has 10 teats, though this does not mean she can necessarily provide sufficient nutrition for 10 puppies in one litter. An average litter consists of about five to six puppies, though this number may vary widely based on the breed of dog. Size of the breed is correlated with litter size. Miniature and small breeds average three to four puppies in each litter, with a maximum litter size of about 5–8. Large and giant breeds average 7 puppies per litter but can have a maximum litter size of about 15. In one study, the Rhodesian Ridgeback had the highest average litter size with 8.9 pups per litter while the Pomeranian and Toy Poodle had the lowest with 2.4 pups per litter. Some breeds have been developed to emphasize certain physical traits beyond the point at which they can safely bear litters on their own. 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). Between 8 days and 8 weeks, 1% will die. Litter size, breed size and age of the female is associated with increased risk. High risk breeds for stillborn includes the Dogue de Bordeaux (14.2%), St. Bernard (12.3%), Chow Chow (12.1%), Pembroke Welsh Corgis (11.7%) and Dalmatian (10.6%). The Basenji, Italian Greyhound, Australian Terrier, Irish Soft Coated Wheaten Terrier and the Bichon Havanais had few to no stillborns (0 0.6%). High risk breeds for early neonatal mortality includes the Rhodesian Ridgeback (11.6%), Dogue de Bordeaux (10.4% ), Dalmatians (8.8%) and Icelandic Sheepdog (8.7%) while the Basenji and Tibetan Terrier had no early neonatal mortality and the Border Terrier and Danish Swedish Farmdog had <1% early neonatal mortality. Common causes of early neonatal mortality are bacteria infection, fetal asphyxia and fading puppy syndrome. Other causes may include elective euthanasia because of congenital defects or failure to meet breed standards. Inbreeding depression is a reduction in progeny fitness due largely to the homozygous expression of deleterious recessive mutations. The gray wolves (Canis lupus) of Isle Royale National Park, Michigan, USA were a small highly inbred population that was considered to be at the threshold of extinction in 2019. This wolf population had been experiencing severe inbreeding depression largely due to the homozygous expression of strongly deleterious recessive mutations. 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.

Because the African wild dog (Lycaon pictus) largely exists in fragmented small populations, its existence is endangered. Inbreeding avoidance via mate selection is characteristic of the species and has important potential consequences for population persistence. Inbreeding is rare within natal packs. Computer population simulations indicate that all populations continuing to avoid incestuous mating will become extinct within 100 years due to the unavailability of unrelated mates. A likely mechanism for avoidance of inbreeding is independent dispersal trajectories from the natal pack. Many of the young wolves spend time alone or in small non breeding packs composed of unrelated individuals. The union of two unrelated individuals in a new home range is the predominant pattern of breeding pair formation. Grey wolves and Arctic foxes also exhibit inbreeding avoidance. Inbreeding is ordinarily avoided because it leads to a reduction in progeny fitness (inbreeding depression) due largely to the homozygous expression of deleterious recessive alleles.

Female dogs are at risk for endometritis and pyometra in the postpartum period and after estrus or vaginitis. 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. Uterine infections should be treated expeditiously if suspected. Contrary to common belief, uterine infections can strike any intact female, whether she has been bred or not, and whether it is her first season or not although it is more common as dogs become older.

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 the male's penis into the latex sleeve. The male ejaculates and the semen is collected in the tube. The semen is then drawn up into a long thin pipette.

Designer breed dogs are mixed breed dogs intentionally bred from parents of two established breeds. Studies have shown that cross bred dogs have a number of desirable reproductive traits. Scott and Fuller found that cross bred females were superior mothers compared to purebred females, producing more milk and giving better care. These advantages led to decreased mortality in the offspring; however, the qualities of such dogs are not predictable. For example, Labrador x Poodle ("Labradoodle") can inherit the coat of either a Labrador, a poodle, or a remix.