The B-727 had a cargo heat switch on the flight engineer's panel. It's been a long time, was this switch off for takeoff? Or, was it one that you closed at top of descent before you pulled the lever to silence the gear horn as the throttles came back?
When I flew 727s the only time the forward baggage heat valve switch would be closed would be for a pressurization problem in the cabin and one needed additional bleed air for the cabin. All other times it was left on during normal operation.
Therefore no live animals were to be placed in the forward baggage compartment.
The switch on the FE's panel was called the puppy snuffer switch.
The captain in this situation made the correct decision.