The cattle fell off the back of a stock truck that was travelling from Yass to Goulburn at about 6.30pm, police said.

One cow was killed instantly while officers were forced to put down the injured animal after they fell from the B-double into Hume Street’s breakdown lane.

Police said the rear gates were not secured but they were investigating who was at fault.

Traffic in one lane was disrupted for two hours while authorities cleared the scene.

Goulburn Mulwaree Council staff also attended.