The abattoir's owner said no horse with false paperwork had ever knowingly been slaughtered there.
The abattoir was closed last week after a visit from an FSA veterinary manager.
Tesco supermarket has extended its ban on Isle of Man meat sales after the abattoir failed a second inspection.
The supermarket giant, one of the abattoir's biggest clients, removed all Manx meat produce from its shelves last February after a routine inspection.
In a report by the BBC, the abattoir insists that its labeling and procedures are above board, with horsemeat and beef kept clearly apart.
FORBES: The Romanian Horse Cart Ban That's (Probably) Behind Europe's Horse Meat Scandal
The abattoir has not yet responded to the request from the sanctuary, but animal rights campaigners in Dundee and Norwich are confident Bertie will survive.
The supermarket giant had been one of the abattoir's biggest clients.
In one instance, a cow fell off the processing line and was chased through the abattoir before having its legs cut and being stabbed to death, she said.
Last year overcapacity at the abattoir sent hog prices plummeting.
Speaking to BBC Northern Ireland's Spotlight programme, a man claiming to be part of a criminal gang said he had delivered horses to the abattoir on "multiple occasions" on forged papers.
The Essex abattoir where the first suspect animal in the current outbreak was identified normally kills animals brought from the Isle of Wight in southern England, from Scotland and from Northern Ireland.
The Gaerwen abattoir is one of the largest in Britain, mainly supplying supermarket chains.
The Kravys abattoir, named as the source of the Comigel meat, insists that its labelling is correct, with horsemeat and beef kept clearly apart.
The former abattoir opened as a shopping centre two years ago during the recession.
Unfortunately, the gristle and the guts the ugly secrets of the Brown abattoir have been gruesomely displayed for all to see.
The Polish abattoir linked to beef found in Newry that contained horsemeat, has said it does not process equine products in its factories.
The supermarket giant removed Manx meat from its shelves last February after a routine inspection of the Manx abattoir raised concerns over standards.
The Kravys abattoir, in Botosani, northeastern Romania, slaughters 3, 000 to 4, 000 horses annually and exports the meat to Sweden, the Netherlands, Bulgaria and Poland.
FORBES: The Romanian Horse Cart Ban That's (Probably) Behind Europe's Horse Meat Scandal
The final stages of the cull of 40, 000 animals on Anglesey - which involves the Gaerwen abattoir - is expected to resume on Monday.
In north Wales, the Environment Agency is investigating how hundreds of young brown trout and eels died in a stream near the Gaerwen abattoir on Anglesey.
"In one second - maybe two if it's a bull - the animal is gone, " says Mr Rosenzweig, who trained for years in Israel and now slaughters once a week, under the observation of a state veterinary official, at the Amsterdam Abattoir.
Mr Rhodes said the FSA had a presence in every abattoir in the UK and tested 90, 000 products a year, for bacteria such as listeria and salmonella.
Singapore, another major market, is restricting purchases to 28 appro ved farms in neighboring Johor state. (Although the death of a Singapore abattoir worker roused concern, the Lion City has since declared itself free of the virus.) Domestic sales of pork have dropped by 70%, as have prices.
The head of the Food Standards Agency, Sir John Krebs, said a loophole under existing rules meant beef was exempt from strict controls if the animal was killed on a farm or at an unlicensed abattoir for the farmer's personal consumption.
The FSA said the Red Lion abattoir in Nantwich could be a risk to public health after it had not followed recommendations from its vets.
The owner of the Red Lion abattoir, High Peak Meat Exports, is licensed to sell horsemeat to Europe and said it openly and legitimately bought horses from Ireland.
The sporting arenas have been built and tested, and the main Olympic gathering-place, on the site of an old abattoir at Homebush, west of Sydney, is ready for the opening ceremony on September 15th.
But the birds were slaughtered, it seems, at an abattoir where poultry from the affected zone were also killed.
An investigation has been launched into an abattoir by the Food Standards Agency (FSA) after undercover filming allegedly showed horses being abused.
BBC: Nantwich horse abattoir investigation after secret film
It is being built on the Joneses 600-acre (243 hectares) beef and arable farm, and will be fed with maize and waste from the St Merryn Meat abattoir in Merthyr Tydfil.
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