One appliance and crew from Broughton, one from Newport Pagnell and two from Northamptonshire attended, along with one officer.
One man and one woman were out and being assessed by South Central Ambulance Service, before they arrived.
The hose box was on its side in lane four of the motorway with two horses, standing upright, within it.
The motorway was closed while firefighters helped to release the horses from the horsebox and reload them into a replacement horse box.
They made the scene safe and left the incident in the hands of National Highways.
