Male sub fertility can be a distressing situation. Recent guidelines point that for optimum fertility a man needs 15 million sperm per ml of  ejaculate with atleast 42% of them moving rapidly forwards. A simple semen evaluation is a good way to begin investigating in most cases. It's also important to get a doctor to physically examine and do relevant tests to check for Diabetes and thyroid disorders. Treatment for male sub fertility is very important and can be as simple as life style changes, Anti oxidants or sometimes IUI/ART.