I have taken my female for a cervical culture every season after the first for obvious reasons the first could not be detected one month before. Not just for breeding purposes but to check the dog is healthy for the upcoming season. Peace of mind. Not all miscarriages are caused by infections and some slight unknown showing on the slide does not always warrant antibiotics. It is best to take your female at least one month before so that the vet when finding anything abnormal can treat that infection before it becomes damaging and then prescribe the correct antibiotic for that particular type of infection. DIY with a broad spetrum antibiotic will not always treat a particular infection and it is best to go to the vet who knows how to treat and with which antibiotic.