I know for airlines that carry crated animals (dogs), the airline is responsible to offer water every so often, and food every so often (the law specifies times, but I don't remember them exactly). I was thinking the 750 mile limit was a screwy way around such, but 750 mile trip could easily be more than 12 hours. Which now makes me think of something else... if checked as luggage will all baggage cars now be required to be A/C and heated, and the conductor legally responsible to ensure such is kept functional? Again, attempting to parallel airplane requirements.
There was a story a while back, of a dog that was being "exercised" by an airline employee, but got away, at JFK. I think it was never seen again.