Agriculture Minister Michelle O'Neill told the assembly investigations were being carried out to detect if Schmallenberg virus was present in sheep, on 5 March 2012.
The minister was briefing the assembly on the recent meeting of the North-South Ministerial Council (NSMC) on agriculture.
Replying to a question from the DUP's Paul Frew, Ms O'Neill said the virus had been discussed at the meeting.
The "targeted surveillance" was centred in birth deformities in sheep, the minister said, and she appealed to farmers to contact the department if they had any concerns.
Other matters discussed at the NSMC meeting included reform of the EU Common Agricultural Policy, and animal health.
Kieran McCarthy of the Alliance party asked about the health and welfare of circus animals.
Ms O'Neill said "non-farmed animals" had not been discussed at the meeting but she was happy to address the matter if Mr McCarthy wrote to her.