The bodies of 30 guinea pigs "in varying states of decay" have been found buried at the entrance to a badger sett, the RSPCA has said.
The charity said the rodents were discovered at the sett in a rural area near Warrington on Sunday.
RSPCA inspector Jenny Bethel said it was "a really strange discovery" and appealed for information.
She added that the animals, which were not microchipped, seemed to be buried "in a pile underneath each other".
A spokesman for the charity said the guinea pigs were discovered by members of the Wirral and Cheshire Badger Group, who had spotted animal fur sticking out from "the surface of fresh, loose soil around the sett entrance".
He said there was "no CCTV covering the area that might provide a clue as to how they met their fates".
"At this stage, there is no indication whether they died at the same time or whether they have been placed in the ground over a longer period," he said.
He added that the find was reported to Cheshire Police's Rural Crime Team, but it remained "unclear" whether the find had "anything to do with the cruel and illegal activities of badger baiters".
Ms Bethel said she had "no idea at this point why the guinea pigs would be in this location".
"They were blocking one of the entrances to the sett, yet it doesn't look like the badgers have shown any interest in them," she said.
She said they might have been put there "because there was a hole already there", but it "may be the case they haven't been dumped all at the same time as they are in different stages of decay".
Ms Bethel asked anyone with information about "suspicious activity in a rural area of Warrington or knows of someone who has owned a large number of guinea pigs over a period of time" to get in touch.