What age is a mastiff fertile?

Mastiffs typically reach sexual maturity between 6 to 12 months of age. However, females generally have their first heat cycle around 6 to 12 months, while males may become fertile a bit later. It's important to wait until they are fully grown, usually around 2 years of age, for breeding to ensure the health of both the dog and its offspring. Always consult a veterinarian for guidance on breeding practices.