Livestock lorries were turned away from the St Merryn Meat abattoir, Merthyr Tydfil, Glamorgan when it was linked to the latest confirmed case of foot and mouth in Surrey.
Slaughtering and processing was halted at the plant, which employs 1000 workers, when routine stock tracing revealed it received cattle from the infected farm before movement was banned.
The animals were inspected by vets on arrival and after slaughter and no signs of disease were spotted.
Elin Jones, Welsh assembly rural affairs minister, emphasised that the closure was routine, but she admitted it was a timely reminder that Wales was still vulnerable to a disease incursion.
The company was later allowed to restart meat processing and packaging and is expected to restart killing on Thursday.
But Ms Jones told assembly members that the Cig Cibyn specialist export abattoir at Caernarfon was likely to stay shut as long as overseas sales were banned.
“My officials will continue to liaise with the directors and with officials from Gwynedd County Council until the conditions for normal trading resume,” the minister said.
She also announced that a new text service would be available to farmers from Thursday to provide key messages about outbreak developments and information about changes to control measures.
Farming unions this week warned Ms Jones that their members were furious about the fall in lamb prices since movement restrictions were imposed.
They claimed that downward pressure on prices could result in more spontaneous demonstrations outside retail outlets like the one staged in Ruthin, Denbighshire this week.
Emyr Jones, Farmers Union of Wales deputy president, said he well understood demonstrators’ frustrations when they saw prices tumbling.
Both unions urged the minister to call on supermarkets to support the industry rather than taking advantage of the impact of foot and mouth.