Pregnancy in the dog (all breeds) lasts about 2 months: 60-64 days.

The canine reproductive life varies greatly from breed to breed with regard to onset of puberty, however. Small breed dogs typically start having estrus (heat) cycles earlier, at 4-6 months of age, and large breeds typically start later, at 12 to 24 months of age. The estrus cycles vary between each individual dog, average of 7 to 10 days. Some dogs as few as 2 days, some dogs cycle as long as 21 days.*

For more on Pregnancy and Birth in animals, please see:

*From the Merck Veterinary Manual, 8th ed. page 980

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