DNA testing has revealed the presence of horsemeat in prepared hamburgers sold in certain supermarket chains in the U.K. and Ireland, according to the Irish federal food safety board. Thirty-seven percent of the "beef" products tested in the routine study were found to be positive for equine DNA.

The study, led by the Food Safety Authority of Ireland (FSAI) in Dublin, also revealed that 85% of these products contained porcine DNA (pig meat).

The quantity of horsemeat was "at low levels" in nine of the ten products that were positive for equine DNA, according to a statement on the FSAI website. However, in one product–the "Everyday Value Beef Burger" marketed by the Tesco supermarket brand–horsemeat made up more than 29% of the "beef" patty. The meat from all sample products had been processed in two plants in Ireland and one in the U.K.

"There is no clear explanation at this time for the presence of horse DNA in products emanating from meat plants that do not use horsemeat in their production process," said Alan Reilly, BSc, MTech, CBiol, MIBiol, FIFSTI, adjunct professor at University College Dublin Institute of Food and Health in Dublin and chief executive of the FSAI. "In Ireland, it is not in our culture to eat horsemeat, and therefore we do not expect to find it in a burger