Studies done on beef products sold in Ireland have shown that many of the most popular store-bought brands test positive for horse DNA.

Although authorities believe there’s no health risk involved, they say the inclusion of unfamiliar DNA does make it harder to trace what ingredients have entered the food chain to produce the final product. The Food Safety Authority of Ireland ran the tests, which were meant to locate pig and horse products in the meat, and found that 10 out of the 27 “beef” products they chose tested positive for horse DNA. A whopping 23 of the 27 contained pig DNA. While most of the levels were low, one Tesco product which was tested was found to contain 29% horse meat.

“Whilst there is a plausible explanation for the presence of pig DNA in these products due to the fact that meat from different animals is processed in the same meat plants, there is no clear explanation at this time for the presence of horse DNA in products emanating from meat plants that do not use horse meat in their production process,” Alan Reilly of the FSAI said.

An investigation has been launched to determine where the horse meat originated from and how it ended up in so many different types of food.

So far, the affected meat has come from Tesco, Dunnes Stores, Lidl, Aldi and Iceland stores in Ireland.