In my experience from practicing neigong I find that you do lose qi when you ejaculate. I feel a drop in energy and if I try to practice my meditation afterwards, it actually hurts my lower dantien. There is an actual physical pain on my dantien and it becomes unbearable to a point where I can't even practice. That's why a lot of chi cultivation schools stress that you should not practice within 3 days after ejaculation. But luckily there is a way around this problem. It's possible to have orgasms without losing semen by squeezing your PC muscle right before ejaculating.
http://www.beautynationpl.com/en/sexual_performance.asp?pageID=8master_male_orgasm
http://www.amazon.com/Taoist-Secrets-Love-Cultivating-Sexual/dp/0943358191/ref=pd_sim_mov_2
