Farmers had hoped that on arrival in the Irish Republic stock would be driven to Belfast's Aldergrove Airport for airlifting to the Continent.
The ferry company's decision dismayed the farmers. More than 500 met at Llanrwst, Gwynedd, to be told their presence at the port would not be welcome.
John Cooke, the Assistant Chief Constable of North Wales police, said: "The problem would not be solved by farmers going to the port."
Animal welfare campaigners who have picketed the Anglesey port for the past week held a special service yesterday to commemorate the death last week of Jill Phipps who was crushed to death after falling under a livestock lorry's wheels at Coventry airport.
The decision at Holyhead followed hard on the heels of the rejection by Dyfed County Council of a Farmers' Union of Wales application to fly calves to Europe from Withybush aerodrome near Haverfordwest.
The airfield is owned and operated by the local authority.
Bob Parry, president of the FUW, said at the weekend: "It is not exaggerating to say that farming is at the crossroads.
"The UK puts pets before food production and that is the road to ruin."
A former policeman, Ronald James, who now runs a business as a bull-hirer in Dyfed, claimed that the ban on flying calves from Withybush meant that he would face bankruptcy in a couple of years.
He said that farmers should link arms to seal the airfield's perimeter.
"The demonstrators would have no chance to break through," Mr James said.
Campaigners unfurled banners on the ramparts of Parliament yesterday to protest against the live export trade and in memory of Ms Phipps.
The protesters said they were enraged by the filibustering tactics used by Conservative MPs on Friday in the House of Commons to defeat a private member's Bill designed to ban live exports.
They also wanted to show their solidarity with Nancy Phipps, Ms Phipp's mother, who said yesterday that she would be willing to die for the cause of animal welfare.
The ad hoc group of hardened campaigners, affiliated to no specific organisation, came together last week to plan the protest but most had worked together before. They launched their boat from Putney, and managed to unfurl two banners before being arrested. They were released without charge.
Dave Wetton, 51, a former national secretary of the Hunt Saboteurs Association, said: "We're a team that comes together very quickly. Most of us have known each other for at least 20 years and can be relied on not to ask too many questions."
The protest against the trade is also gathering momentum in Plymouth, Devon.
Although the next shipment of animals is not expected until tomorrow, the protesters are organising surveillance rotas on local cattle enclosures and setting up "telephone trees" to get hundreds of people to the dock entrances in time to stop the trucks entering the port.Reuse content