Senior Constable Steve Griffiths, of Milton, said a Nyhon Transport truck was being driven along Lakeside Rd, about 10km south of Milton, about 10am, when a front tyre blew on the trailer, causing it to roll on to its side.
Snr Const Griffiths said about half the 28 cows in the trailer immediately fell on to the road.
Passing motorists managed to control the cows until police and fire officers arrived. The other cows were trapped in the trailer until freed.
Snr Const Griffiths said none of the cows died, although a few had minor cuts. The animals were checked by a veterinarian.
The truck unit did not roll, and was not damaged. Const Griffiths said the driver would not face charges.
The truck had been travelling from Kaitangata to Mosgiel.
