A truck carrying cattle veered off the road and overturned on the westbound Highway 20, near the south shore town of Ste. Helene de Bagot, early Thursday.
According to the Surete du Quebec, the driver lost control of the vehicle and it flipped onto the median.
The truck was carrying about thirty cows, and a dozen were thrown from the vehicle during the accident. Police euthanized six of the animals while local veterinarians were called to the scene to euthanize others.
Some of the animals were seriously hurt and others posed threats to drivers, police said.
In all, only six cows have survived the accident, police say.
One lane of the highway heading west toward Montreal was temporarily closed in the area.
The cattle were headed for an abattoir in Ontario. The driver was taken to a hospital as a precaution.
Initial reports indicate the driver may have fallen asleep at the wheel.
