The Food Safety Authority of Ireland reported that 37 percent of the burgers it tested showed traces of horse DNA, The Daily Telegraph reported. Some Everyday Value Beef Burgers were as much as 29 percent horsemeat.
"The presence of illegal meat in our products is extremely serious," said Tim Smith, a Tesco executive. "Our customers have the right to expect that food they buy is produced to the highest standards."
Investigators also found horse DNA in ground beef products sold by Iceland, ALDI, Lidl and Dunnes, officials said.
Pig DNA was reportedly discovered in a wide variety of beef products. This raises questions for Jews and Muslims whose dietary rules ban pork.
Beef containing horse DNA came from Liffey Meats and Silvercrest food processing plants in Ireland and Dalepak Hambleton in North Yorkshire.