In a statement, the department said that ABP Food Group, who operate the plant, had indicated that none of the meat had entered the food chain.
The investigation is focusing on the full supply chain including the meat trader concerned and others who facilitated the purchase of the product and its transfer to users in Ireland.
Traces of horsemeat were found in processor Silvercrest, also managed by the ABP Group.
DNA was also discovered in food suppliers Liffey Meats and Dalepack Hambleton.
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