Edit: http://www.veggieboards.com/boards/archive/index.php/t-3294.html This website says that there is as much as 20 times B12 in semen as there is in human blood serum and http://www.veganhealth.org/b12/levels says that non-vegetarians have about 387 pg/ml of B12 in their blood giving about 7740pg/ml of B12 in semen. Wikipedia says you should intake 5 micrograms per day of B12 therefore you would need 5000000/7740=646ml of semen per day.
i believe any thing your mouth rejects it naturally is bad for you , i was searching how much vitamin b12 you lose in each ejaculation , now here i see people are looking , can they eat semen for vitamin b12 , ha ha ha !, isn't it funny ?!