Approximately three weeks. They are usually receptive to the male for less than a week, usually about day 8 - 14, but can be mated at any time from start to finish, if you know when that is, particularly iasyou don't always notice them first coming in. You don't always notice any bleeding as some bitches are very clean or have 'clear' seasons. Make sure she can't get out, or she will go looking for a mate!