From a story on abcnews.go.com by Riley Hoffman headlined “Plane forced to return to JFK Airport after horse on board gets loose:”

A 747 cargo plane heading to Belgium from New York was forced to return to John F. Kennedy International Airport after a horse escaped from its stall, according to the air traffic control audio.

According to the audio clip, the horse got loose within 30 minutes of takeoff.

The Boeing 747 was barely at 31,000 feet when a pilot told air traffic control that a horse had escaped from its stall and that they needed to return to JFK, according to FlightRadar24.