The Department of Agriculture and the Food Safety Authority have launched an investigation into the discovery of contaminated animal feed.
It follows the discovery of toxic pollutants in pork fat.
A number of farms are now under restriction by the Department of Agriculture.
Animals on the farms will not be allowed to enter the food chain unless they are shown to be free of the contaminant.
The problem was identified during routine monitoring of the food chain for a range of contaminants.