I was 10 years old when this originally aired on television. My dad said he wouldn't let me watch it because it supposedly had a scene of a dead horse getting cut up with a chainsaw. I thought at the time he was just being mean.
shareI haven't seen Senior Trip so I don't know if this is the movie with the scene you remember from childhood.
However, I can tell you that such a scene exists in Animal House (1978). Our heroes kidnap and unintentionally kill cadet Weidermeier's pet horse in the dean's office (heart attack from a gun firing). In the next scene, in the dean's office, characters are discussing what happened on a couch that obscures the dead horse for all but his rigid four legs standing straight up in the air. As that scene ends, the janitor comes in to remove the horse and revs up a chainsaw. We don't see it actually happen, but the receptionist outside the office reacts comically to the noise.
I think the dead horse in the bed scene happened in the one of The Godfather films.
Definitely not in this film!