The demonstration was staged on the cathedral green by animal rights campaigners while NFU and Young Farmers services take place inside the cathedral.
Protesters wore badger masks and held placards outside as the Devon Young Farmers Harvest Thanksgiving service took place.
Young Farmers Club, which is who the service is being held for, is an organisation that dates back to the 1920s.
One passer-by told Devon Live: "They were singing a song All Thing's Bright and Beautiful, but they changed the second bit of the verse to "The NFU killed them all" instead of the Lord God made them all.
"The singing was directed at those arriving for the service and going in the door. As you can imagine there was no one else there, no public and it's pitch night. They all had badger masks on."
Devon and Cornwall Police sent liaison officers to the cathedral but no disruption to the service inside the cathedral and no arrests were made.
It is not clear which anti-badger culling group was behind the protest at this stage.
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