A suspected case of avian influenza, or bird flu, has been detected on a poultry farm in Co Monaghan.
It is understood samples have been taken from the site and have been sent to a laboratory for confirmation.
If confirmed, it would be the first case of bird flu on a commercial farm in the country this year.
It is understood that the suspected outbreak was reported to the Department of Agriculture yesterday evening.
The flock in question is believed to have around 45,000 laying hens in an enriched cage system, meaning they are not a free-range flock.
The farmer is understood to have contacted his veterinary practitioner yesterday evening after 400 birds were found dead in the previous 24 hours.
The veterinary practitioner is believed to have immediately informed officials, who verbally restricted the flock and commenced preparations.
Today, officials are understood to have visited the holding in the north of the county and took samples, which are understood to have been delivered to the department's laboratories this afternoon.
Initial results are expected by tomorrow morning with further results possible by tomorrow evening.
Only 30 birds on the farm reportedly died today, compared to the 400 reported dead yesterday.
It is understood that this reduction in mortality would not usually be typical of an avian influenza outbreak, although it is still possible.
Since December, five cases of the virus have been detected in wild birds.
Last week, there was a suspected case on a poultry farm in Co Tyrone, where 64,000 birds were slaughtered to prevent any possible spread of the virus.
From the beginning of this week, a housing order for all poultry and captive birds has been in place in Ireland, meaning they must be kept indoors and separated from potentially infected wild birds.
A similar order is in effect for the north.
Additional reporting Marc O'Driscoll
