You know, I was recently thinking about it.
Semen is supposedly changed in taste and look depending on your diet. Acidic, sweet, salty, bitter, etcetera, are all dependent on what you drink and eat, as well as if you smoke, do certain drugs, have certain medication and so on.
So, if a Vampire's diet mainly consists of blood, what exactly would his semen be like? Taste? Texture? Would he even have sperm, since, in most Vampire lore, they are the undead? What about female Vampire's ejaculatory fluids?