A cat's first litter is often considered the purest because at this stage, the cat's genome has not yet been affected by too much genetic variation. At this time, the mother of the cat passes on her best genes to her daughter, ensuring the genetic qualities of the cubs. In addition, cats' first litters are usually born at a younger age, when their bodies are not yet fully developed. Therefore, more meticulous care is needed to ensure the healthy growth of the pups. 
While first-born cats are usually the most purebred, this does not mean that all purebred cats should be bred at the time of their first birth. For purebred cats, breeding should be based on a science-based breeding program and a stable gene pool to ensure the genetic health and diversity of the breed. Professional breeders will make a reasonable plan to ensure the health of the cat and the quality genetics of the breed. 
When considering the breeding of cats, whether pet cats or purebred cats, it is important to pay attention to their physical health and psychological state. In addition, it is necessary to consider whether their owners and families are suitable for raising new children. Therefore, it is advisable to consult with a professional veterinarian and breeder before breeding to ensure the health and well-being of the cat. 