The best time for dog breeding typically depends on several factors, including the dog's breed, size, health status, and age.

Generally, small dogs reach sexual maturity earlier, around 8 to 12 months of age, while large dogs may take longer, requiring 12 to 24 months. However, reaching sexual maturity alone does not mean that the dog is ready for breeding. To ensure the health of the mother dog and the puppies, it is recommended to wait until the dog reaches physical maturity before breeding.

For most dogs, the optimal breeding age is typically between 1.5 and 7 years old. During this age range, the dog's reproductive organs have fully developed, and the body is in its prime condition, allowing for the production of healthy and robust offspring.

In addition, the timing of dog breeding should also consider seasonal factors. Dogs are seasonal monoestrus animals, typically going into heat in the spring (March to May) and autumn (September to November). During these seasons, a female dog's heat cycle usually lasts around 21 days, and the pregnancy period ranges from 58 to 63 days. Therefore, if you plan to have your dog breed during a specific season, you can arrange a breeding plan based on these timeframes.

In summary, to ensure the health of dogs and puppies, it is recommended to wait until the dog reaches physical maturity before breeding, and choose the best breeding age and season. Additionally, a comprehensive health check should be performed before breeding to ensure that the dog does not have any genetic diseases or other health issues.