There are fears of a full-scale outbreak of the bluetongue animal disease in Northern Ireland.
The Agriculture Minister Michelle Gildernew has confirmed that the disease has been identified in four further animals.
"The cull is being carried out as the latest blood tests on this herd have detected the presence of antibody or virus in another four calves born to this group of cattle," the ministry said in a statement on Monday. " The cull will be completed today."
A total of 27 animals will now be culled on a farm in north Antrim in an attempt to stop the virus spreading.
The first case of the disease was confirmed at the same farm last week in a cow imported from the Netherlands.
"On Friday, the Ulster Farmers' Union called for a voluntary ban in relation to the import of animals from bluetongue-affected areas," Ms Gildernew said.
"I welcome this move and would plead again with farmers - do not import. This experience demonstrates that it is quite simply too risky."
Bluetongue, which is spread by midges, swept across northern Europe last year, reaching parts of England in September.