Possible Clues:

• 'That's big news, dude!'
• "Hold it, horse!"
• 'Stop, horse!'
• Cry to a horse that's the opposite of 'Giddyup!'
• Doctor on TV with a way to stop the trots
• Equestrian's "stop"
• "OMG!" kin
• Oater ''Hold it!''
• 'Hold it, horse!'
• Doctor brought to a stop