If the dog does not menstruate at the age of 4, it may be that the menstrual period is interrupted, and it may return to normal after a while. However, if the dog continues to not menstruate, it may be premature menopause, or it may be caused by other diseases and needs to be taken care of. The dog should go to the pet hospital for examination to avoid delaying the condition. Generally, dogs will begin menopause when they are seven or eight years old, and menopausal dogs cannot become pregnant again.