Donkey semen will not be served on network TV tomorrow night -- the"Fear Factor" episode featuring the stunt has been yanked ... at least according to a website where NBC posts its media releases.

The controversial episode is entitled, "Hee Haw! Hee Haw!" An NBC media release teased it by saying the contestants will eat "the unimaginable."

But the NBC website no longer lists that episode as airing tomorrow ... and instead lists a repeat of an episode entitled "Snake Bite" -- which first aired on January 2.

We also checked two channel guides -- one in LA and one in NYC -- and both now list the repeat instead of the one with the donkey semen stunt. Additionally, promos for the episode are no longer posted anywhere on the Internet.

TMZ broke the story ... NBC had given 'FF' producers the thumbs up on airing the episode -- but according to our sources honchos at NBC and its parent company, Comcast, started having second thoughts after TMZ published details of the challenge.

We've made several calls to reps at NBC, Comcast, and Endemol -- which produces 'FF' -- but so far ... radio silence.

The good people at the peacock just got back to us -- NBC Entertainment Chairman Bob Greenblatt says, "I reviewed the episode late last week and decided it was a segment we should not air."