ejaculate odor

I've been dating a 44yr old male for almost a year now. He's very athletic and in pretty good shape. I've noticed the last time he and I had sex there was a very strong smell upon him ejaculating. It's a weird smell something I've never smelled before. I asked him about it and he doesn't know why he has that odor. We talked about him having any pain anywhere, and he did mention lower back pain. I haven't had any vaginal issues, but thought I should get checked anyway. Would you be able to tell me what this could possible be?

[gymdandee]

Usually, semen is a white or off white fluid that within about 30 minutes turns runny and clear. Any changes in colour or smell could be a sign of something more serious.
Semen will usually have a chlorine type smell, but a strong foul smelling ejaculation could be a sign of infection. Yellow or green tinged semen could also indicate infections and red or brown semen can be prostate problems.
If you see any of these changes see your doctor.