Complex sentence: When the professor's absence was discovered minutes before the scheduled broadcast, janitor Barber was called in as a substitute, so the future sportscaster's first gig was reading "Certain Aspects of Bovine Obstetrics".
Split into simpler sentences: When the professor's absence was discovered minutes before the broadcast was to begin, janitor Barber was called in as a substitute. Thus the future sportscaster's first gig was reading "Certain Aspects of Bovine Obstetrics".