DUBLIN (AP) -- Ireland's government says DNA testing has discovered that Polish meat offcuts imported into Ireland and labeled as beef actually contain up to 75 percent horsemeat.

Agriculture Minister Simon Coveney says police have joined the 3-week-old Irish investigation after a second Irish meat processing plant was discovered to be using the suspect Polish product in making beef burgers.

Coveney's department said Monday that tests have found a sample of the product at Rangeland Foods labeled as "beef" was actually three-quarters horse.

Previous Irish tests on completed burger patties, rather than the ingredient itself, have found two burgers made of 29 percent and 18 percent horsemeat, respectively.

Polish authorities insist their own testing of slaughterhouses implicated by Ireland has not turned up any evidence that any of them handled horsemeat.

Copyright 2013 The AP.