Animal control workers and Los Angeles firefighters were called to the scene near Polk Street shortly before 11 a.m., prompting a full closure of the westbound lanes. All westbound lanes were reopened shortly before 5 p.m.
Los Angeles Fire Department spokesman Brian Humphrey says three sheep and a dog were rescued and appeared uninjured. Two cows were pinned down and could not get up. Firefighters cut a hole in the overturned trailer and hoisted them out with a large hydraulic boom before loading them into another vehicle for transport.
One cow had a severely broken leg and had to be euthanized, while the other cow, which was pregnant, was expected to be okay, said Jay Weiner, co-founder of the Gentle Barn Foundation, a non-profit animal rescue service that assisted.
The male driver was taken to a hospital in serious condition.
The cause of the crash remains under investigation, but the truck had a flat tire, CHP Officer Gordon Verrone said.
PHOTOS: Animals rescued from overturned trailer on 210 Freeway
City News Service contributed to this report.