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In domestic dogs, sexual maturity (puberty) occurs between the ages of 6 to 12 months for both males and females, although this can be delayed until up to two years of age for some large breeds. Pregnancy is possible as soon as the first estrus cycle, but breeding is not recommended prior to the second cycle.
Some dogs would come into heat earlier than six months and can get pregnant in the first heat although it is advisable to breed the dog when it is about 2 years old or after the dog has gone into the 2nd or 3rd heat.ome dogs would come into heat earlier than six months and can get pregnant in the first heat although it is advisable to breed the dog when it is about 2 years old or after the dog has gone into the 2nd or 3rd heat.