About 10 tonnes of the animal swill spilled onto the A354 near Winterborne Whitechurch, between Dorchester and Blandford, at about 00:30 BST, Dorset Police said.
Specialist equipment was used to clear the "greasy" non-hazardous waste from the road, the force added.
The road was closed for several hours but has since reopened.
Liquid pig feed spilled on to and closed a road after fermenting in a tanker in Dorset.