What is a Vasectomy? A vasectomy is a simple procedure where the vas deferens (vas) the is cut to cause sterilisation in a male. The vas is a tube that carries sperm from the testicles to the penis. On the way, sperm is joined by semen so your ejaculate contains both sperm and semen. Sperm makes up a very small percentage (less than 5%). Because we are only stopping sperm being made, most men will not notice any change in the volume of their ejaculate after a vasectomy. For more information on Vasectomy, visit our Male Sterilisation page.