Scientific tests on beef products sold in Tesco, Dunnes Stores, Lidl, Aldi and Iceland uncovered low levels of horse DNA.
Beef burger products which tested positive were produced by Liffey Meats and Silvercrest Foods in Ireland and one UK plant, Dalepak at Hambleton, in North Yorkshire.
Professor Alan Reilly, chief executive of the Food Safety Authority of Ireland (FSAI), said there was no health risk but also no reasonable explanation for it to be found.
“The products we have identified as containing horse DNA and/or pig DNA do not pose any food safety risk and consumers should not be worried,” he said.
According to the research by the FSAI, one sample of burger goods, Tesco Everyday Value Beef Burgers, showed about 29 per cent horse meat relative to beef content.
All the retailers said they are removing all implicated products from their shelves.
The FSAI analysed 27 beef burger products with best before dates from last June to March 2014 with 10 of the 27 products – 37 per cent – testing positive for horse DNA and 85 per cent testing positive for pig DNA.
Some 31 beef meal products such as cottage pie, beef curry pie and lasagne were tested with 21 found to be positive for pig DNA. All tested negative for horse meat.
The FSAI analysis also found traces of horse DNA in batches of raw ingredients, including some imported from the Netherlands and Spain.
The DNA tests found horse in the following products: Tesco Everyday Value Beef Burgers 29.1 per cent; Tesco Beef Quarter Pounders 0.1 per cent; Oakhurst Beef Burgers in Aldi 0.3 per cent; Moordale Quarter Pounders in Lidl 0.1 per cent; Flamehouse Chargrilled Quarter Pounders in Dunnes Stores 0.1 per cent; two varieties of Iceland Quarter Pounders 0.1 per cent.
Even lower levels were recorded in Moordale Beef Burgers in Lidl and St Bernard Beef Burgers in Dunnes Stores.
Tesco said: “We are working with the authorities in Ireland and the UK, and with the supplier concerned, to urgently understand how this has happened and how to ensure it does not happen again. We will not take any stock from this site until the conclusion and satisfactory resolution of an investigation.”
Aldi said: “We have sought information from one supplier, Silvercrest, which is dealing directly with the FSAI on the issue that has been raised.”
Lidl said: “A refund will be provided to customers who wish to return affected products.”