The withdrawal period for two makes of organophosphate sheep dip has been temporarily extended from 35 to 70 days.
Farmers using a third organophosphate – Paracide 62 – are already required by the manufacturer and the government to wait for 70 days.
The Veterinary Medicine Directorate said that the temporary extension for the two sheep dip products has been brought in to ensure the safety of people eating sheep products.
The extension has been needed following a modification of the formula for the sheep dips which means the manufacturer is gathering evidence that a shorter waiting period is safe.
Over 4000 samples of sheep kidney have been tested for residues of organophosphates since 2005. No residues have been found.