The road at the Longbridge Island was partly closed on Tuesday evening as emergency services and fire crews spent several hours on the clean up operation.
The road was fully reopened several hours later on March 29, but officers are now appealing for drivers to help track down the offender responsible for the chaos.
A police spokesperson said on Tuesday evening: “All lanes of the A46 are now open at Longbridge Island.
“Investigations are ongoing and we will be dealing with the incident positively.”
“Did you witness spillage of pigswill onto A46 near junction 15 of the M40?
“Any witnesses please call 101 quote 0209 290316.”