Gestation and Litters
Gestation in a dog is 60 days in length, however the length appears to vary to the lay person. This is due to the longevity of sperm in the female tract. Canine sperm can live for 10 to 11 days in the uterine tubes (fallopian tubes) so if a bitch 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.
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. This 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, an English Bulldog has wide shoulders and narrow hips, thus the breed requires artificial insemination and, later, a 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.
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 bitch 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 Havanaise had little 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.
Other multi-breed studies have put stillborn rates at 6.5-7% and early neonatal mortality at 11.5-19.8%.
Read more about this topic: Canine Reproduction