Gardai from the National Bureau of Criminal Investigation yesterday joined an inquiry into the source of the foot-and-mouth outbreak on the Cooley Peninsula.
There is believed to be a strong possibility that foot-and-mouth disease reached north Louth from Meigh in Co Armagh - a distance of four miles.
A spokesman for the Department of Agriculture confirmed it is now treating the Louth case as secondary to the Meigh outbreak and its investigation was focusing on the connection between both.
It is believed attention is being paid to the origin and movements of sheep in flocks that may have been stored on land close to the infected flock in Co Louth. At least one person has met detectives on the issue of particular sheep movements.
However, the Department spokesman said "it is possible we may never find out" the precise cause of the Louth outbreak.
Throughout yesterday the grim implications of the presence of the virus in just one flock became clear. At 8 a.m. the former AIBP abattoir and meat plant at Ravensdale, which is within the 3 km exclusion zone, started to slaughter all sheep, cattle, pigs and goats within the 1 km perimeter.
Outside the plant there was a constant flow of trailers carrying live and presumably healthy animals to slaughter. As they left the vehicles were thoroughly cleaned and disinfected. All were sealed with tarpaulin covers. Inside, they carried the carcasses which are destined for approved rendering plants in either Cavan or Meath.
By late afternoon about 1,600 sheep and 200 cattle had been killed; approximately the same number again were to be slaughtered either last night or this morning. A clinical examination was made of each animal in situ before it was taken alive to the AIBP plant. No suspicious cases were found.
This morning the Department hopes to start slaughtering all sheep in the 3 km zone. Meanwhile, extending the cull to the rest of the Cooley area is also under consideration.
As the day progressed the atmosphere grew tenser. In the village of Carlingford, chatting lunch-time diners stopped and stared in silence at the television news bulletin.
"The shock here is turning to stress. The farmers want whatever is necessary to be done but they say let it happen quickly and now. They don't want this dragged on," the Louth IFA chairman, Mr Raymond O'Malley, said. Farmers who had even part of a field within the zones identified for culling, were losing their livestock.
Yesterday, the Minister for Social, Community and Family Affairs,, Mr Ahern, said he would be making a counsellor available to help farmers through this time.
To conform to the EU ban on exports of livestock, meat and dairy produce from Co Louth an additional 35 checkpoints, some mobile, were established yesterday.
A total of 200 members of the Defence Forces from the Southern Brigade and the Curragh have been transferred to Louth to assist gardai in enforcing the ban and effectively sealing off the county.