Police are appealing for witnesses to a collision involving an articulated lorry on the A421 Tingewick bypass on Monday.
The white lorry was negotiating the Tingewick roundabout, heading towards Buckingham, about 1.45pm, when it overturned, spilling 27 tonnes of chicken feed.
The 40-year-old driver was taken to Milton Keynes Hospital with back injuries.
Officers particularly wish to speak to the driver of a silver BMW which was on the roundabout and would have witnessed the incident. Call PC Liz Johnson on 101.