Sexual maturity in dogs begins to happen around 6 to 12 months ago in males and females, this can be delayed for up to two years old in some large breeds. Adolescence in dogs is around 12 to 15 months, after which they are for the most part more adult than puppy.
The majority of female dogs have their first cycle between 6 and 12 months old. Females experience cycles biannually, in which period her body prepares for pregnancy. As the eggs survive and are capable of being fertilised for a week after ovulation, it is possible for a female to mate with more that one male.
The gestation period for dogs is between 56 to 72 days after fertilisation, with the average being 63 days. The average litter is 6 puppies but this can vary depending on the breed.
Neutering refers to the sterilisation of animals, to eliminate the ability to reproduce.
The hormonal changes involved with sterilisation are likely to change the dog's personality, as well as their metabolism.