When is the best time to breed a dog as my dog is 3 and in season at moment has been for 6 days does it hurt her?

Does it hurt her to be in heat, or season as you say? Yes! Not physically, but it can hurt her mental well being. May I ask why you would want to breed her? It doesn't sound to me like you are doing it for show quality dogs, or to preserve a particular bloodline, or you would know more about the question that you posed.

Do you know how many dogs are in shelters of purebred and non-purebred varieties? Thousands of dogs are killed every single day, not because there is something wrong with them, but because they are there out of circumstance because their owners gave them up.

There are some circumstances where they had loving owners, but the dogs ended up there out of necessity, for example the thousands of dogs that got caught up in hurricane Katrina, and the owners hearts ached because they could not take their beloved family members.

I have had the unfortunate and heartbreaking task of putting a beloved (dog) family member to sleep, for medical reasons. I wish when people decided to breed their pet, that they would first be required to look into the sad and scared eyes of a dog that senses he is leaving you for the last time. Too many of these dogs have no one to be there with them to say goodbye, because they don't understand that his owners recklessly bred his mother, and he went to another home and they didn't want him anymore. Maybe he barked too much, maybe he had trouble learning to pee outside and so on. He wished his human family would have showed him how, and taken the time. He just wanted to please and love you unconditionally, even when his family left him alone for hours. He didn't know your shoes were expensive. He just wanted something to do while you were gone! But when you came home, his tail was wagging away, and he was so happy to see you!

He doesn't understand why his human family didn't do much needed research, or took the time and energy to train him, and now he has to die, because his mother was bred, in a lot of cases to make money.

Spaying and neutering you pets make them more mentally balanced and happy pets. They are easier to train, they are less aggressive, they are easier to socialize, less likely to develop certain health problems, and overall make a more stable and loving pet.

If you care about your pet, please consider this before breeding more unwanted or abandoned dogs. Look into your dogs eyes, and ask her what she could say given the ability. :)

Breeding should be left to those not needing to ask simple, basic questions. Books have been written about it. Rather than ask question here, start reading. Those unwilling to do the work it takes to produce quality puppies should spay/neuter their pets at 6 months.