Restrictions on animal movements have come into force in Wales, in wake of a foot-and-mouth case in Surrey.
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Deputy first minister Ieuan Wyn Jones said there was a "well rehearsed contigency plan" while farming minister Elin Jones has cut short her holiday.
The Gower Show was cancelled altogether, along with cattle and sheep competitions at the Brecon Show.
Farmers' leaders said rural Wales was "holding its breath" but praised the swift response.
An assembly government spokesman said a restricted zone had been put in place across Wales as part of the Great Britain-wide ban on the movement of susceptible animals, after a case of the disease was confirmed at the farm near Guilford.
"No link to Wales from the infected premises has been identified," he said.
Rural Affairs Minister Elin Jones is expected to arrive back early from her holiday in New Zealand on Sunday.
Deputy first minister Ieuan Wyn Jones said people in rural Wales would be "acutely concerned" and urged farmers to continue to be vigilant.
Mr Jones added: żI also want to emphasise that the Welsh countryside continues to be open.
"There are no plans for a blanket closure of footpaths and rural Wales is there for people to enjoy."
Brecon Show organisers said they had contacted cattle and sheep owners on Friday night to tell them their competitions had been cancelled but horse competitions and other events were going ahead.
Vicky Spencer said: "We were expecting 150-180 cattle and 350 to 400 sheep, so it's been a hard task all night.
"But we still want visitors to come - there are still events and the horse exhibition and horse show is still going ahead."
Animal inspectors would be looking at goats and cattle already at the showground and likely to be sending them home.
They include a number of Charolais cattle which had already arrived for the breed's annual show.
The Gower Show, which was expecting 10,000 visitors, was cancelled this morning.
Treasurer Peter Muxworthy said: "We had very little choice, the risk would have been too great - we were told we couldn't have any cattle, sheep or any horses which had been on a farm or been in contact with hay.
EVENTS AFFECTED IN WALES:
Gower Show - cancelled
Brecon Show - cattle and horse competitions cancelled, other events continue
Whitland cattle market - cancelled
Llangeinor Hunt Game Fair (Sunday) - cancelled
"It's going to leave a hole in our finances, perhaps £30,000, as we still have costs to meet, like catering."
A cattle market at Whitland in Carmarthenshire was also cancelled.
Around 390 livestock were due to be sold.
John Nicholas, a partner with JJ Morris Auctioneers, said: "Everybody we spoke to is shocked that foot-and-mouth has raised its head once again."
"We're in Cardigan on Monday, that will be cancelled. There was to be another one here (Whitland) on Tuesday and a sale of sheep here on Friday. But until we get further advice from Defra we are in limbo. "
Sixty animals on a farm near Guildford have tested positive for the disease.
A 3km protection zone has been put in place around the premises and a UK ban imposed on movement of all livestock.
More than 360,000 animals were slaughtered in Wales in the outbreak in 2001.
National Farmers' Union (NFU) Cymru president Dai Davies said: "Everyone living in rural Wales will be holding their breath at the moment, it doesn't just have serious consequences for the animal industry but rural Wales in general."
He said he was pleased that the authorities had acted so quickly, following the lessons learned from the 2001 outbreak.
"There was a total shutdown within minutes of it being confirmed. There will be initial pain but hopefully long term gain."
Gareth Vaughan, Farmers' Union of Wales president added: "We will be providing the Welsh Assembly Government with every appropriate support in order to minimise the impact of the outbreak, and would urge every farmer to do the same."