Infertility in male tom cats is not usually a problem. Unless your a cat breeder with a valuable, champion tom cat, it can’t fulfill it’s reproductive obligation. Veterinarians who specialize in reproductive disorders, will conduct a microscopic examination of the tom cats sperm. Is it mobile and able to move about spontaneously? Does the sperm have the proper morphology?  Other conditions that could affect the fertility of male cats include malnutrition, obesity, too much liver in the cats diet and hypothyroidism. There are pet medications that could control a thyroid problem. Sometimes it just comes down to a weak libido. Luckily there are treatments for most of these problems.