A vasectomy is a simple procedure where the vas deferens (vas) the is cut to cause sterilisation in a male by stopping the flow of sperm into the ejaculate. The vas is a tube that carries sperm from the testicles where it is made 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%), and therefor most men will not notice any change in the volume of their ejaculate after a vasectomy.