Beef from three farms in Ireland have been found to contain dioxin levels above the legal limit.
But the Irish government is not issuing a recall of beef products because it does not believe the contaminated beef would pose a risk to human health.
Tests on 11 herds revealed three contained dioxins two to three times above the safe limits, compared with 80 to 200 times in some pigmeat.
More than 40 cattle herds across Ireland are understood to have been fed contaminated feed.
Nine herds have been placed under restriction in Northern Ireland, including one beef and one dairy herd.
All milk from the dairy farm has been prevented from entering the food chain, officials said.
Irish agriculture minister Brendan Smith said while the contaminated beef would not cause any public health concern, it was “technically non-complaint”.
As a result any animals in herds above the legal limit would be taken out of the food and animal feed chain and any products from these animals would not be released into the market, he said.
Further tests being carried out on carcasses of cattle understood to have been given the contaminated feed are expected at the end of the week.
The Irish Food Safety Authority said if tests came back within acceptable limits those animals would be released into the food chain. The Department of Agriculture, Fisheries and Food said the total number of cattle slaughtered from the 11 herds from September 1 amounted to 3000 – 0.2% of total annual production.