An upcoming episode of NBC’s ‘Fear Factor‘ has the network’s top brass very nervous. The hit TV show calls for contestants to swallow a glass full of donkey semen, followed quickly by a glass of donkey urine to wash it all down.

Sources involved in the production tell us the stomach-churning stunt was shot last summer — but NBC honchos were having a tough time swallowing this one as the air date approached.

Our sources say NBC execs had multiple pow-wows in the months after the stunt was shot … but eventually gave FF producers the thumbs up.

Calls to NBC were not immediately returned.

The episode of Fear Factor, which tests the limits of what humans will do for fame and fortune, airs this Monday.