The meat processing plant Hall's of Broxburn will be closing in the next few months.
Owner Vion announced the closure after a 90-day consultation period with Scottish council bosses and industry leaders.
The plant, which employs 1,700 people and processes more than 70% of Scotland's pigmeat, was loss-making with too much investment needed to make the business sustainable, said Vion.
It will be fully closed by February 2013 but some areas of the business will start to shut down as early as this month.
"We have done everything in our power to avoid having to take this extremely regrettable action, but we have been unable to identify any viable alternative to the closure of the plant," said Vion UK chairman Peter Barr.
"This is a very sad day for all those involved but, unfortunately, the unsustainable losses which the plant continues to suffer, combined with the challenging economic conditions across all food sectors, have left us with no alternative.
"As we outlined when we made our initial announcement in July, Vion has invested tens of millions of pounds in the Hall's site over a number of years, but it continues to record unsustainable losses.
"The outdated and inefficient layout of the site, overcapacity in the marketplace and increasing costs mean that it has been loss making for a number of years - a position we can no longer sustain. "
However, Mr Barr said there is still hope for the plant, should a company come forward to take it over.
"In tandem with the Scottish government, we have been working to find potential new owners for the site and this process has uncovered a small number of interested parties," he said.
"We are engaged in detailed discussions with these parties to establish if their proposals would provide a viable solution for the Broxburn site."
The news was described as "disappointing" by Jim McLaren, chairman of Quality Meat Scotland.
"While this is also a black day for the Scottish pig industry, it is very important to view today's announcement in a wider context," said Mr McLaren.
"History has repeatedly shown that one of the great strengths of the Scottish pig industry is its farmers' ability to adapt and respond strongly in the face of challenge. This professional industry has proved its capacity to exceed customer expectations by delivering top quality, efficiently-produced pigmeat time and time again."
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