8 mo English mastiff how do you know when she in heat and how often will she go into heat?

Answer 1

8 months old is old enough to start cycling, so you should keep your eye on her. Signs of heat include squatting, spotting blood, excessive attention-seeking behavior, loss of leash training when around intact males and nesting behaviors.

She will go into heat approximately every 60 days through the spring and summer; heat cycles may stop over winter or continue depending upon her genetic make-up.

As a veterinarian, unless you know you are going to be breeding her, I strongly recommend having her spayed as soon as possible. In addition to preventing unwanted and unexpected puppies, early spaying also prevents Breast cancer, uterine cancer and ovarian cancer. It also tends to 'mellow out' most dogs, making them less hyper.