The poultry and brewing industries have also been hit by the Europe-wide crisis
The CO2 is used in the high welfare stunning equipment at the recently-refurbished plant, which is operated on behalf of QPP by Tulip.
Normal weekly kill is 6000 but this had been cut to 1800.
NFU Scotland’s pigs and poultry, and animal health and welfare policy manager Penny Middleton, said: “The shortage of CO2 is having a critical impact on the slaughter of pigs and poultry, where gas stunning is the preferred method of slaughter for welfare reasons.
“The processing plant at Brechin has already announced that it will not be able to take any more pigs from today, a decision that will impact heavily on pig units reliant on being able to get pigs away. Any disruption to that flow can result in welfare issues and overcrowding.
“Given the expectation of animal welfare problems on pig and poultry units NFUS feels that it is vital that CO2 supplies are reserved and directed to those plants in need.”
There will be no slaughtering after Monday’s intake, and it is not known when fresh supplies will be available.
Some pigs were heading south of the border to other abattoirs while others were being held back on farm.
The shortage of gas, caused by maintenance shutdowns in the processing of ammonium nitrate fertiliser, of which CO2 is a by-product, appears to have taken the food and drink sector by surprise, with every pig and poultry plant in the UK affected, as well as the brewing and soft drink industries.
The task for Andy McGowan, chief executive of procurement group Scottish Pig Producers, is to convince the gas suppliers and Government that pig abattoirs should be treated as a priority on animal welfare grounds.
He said: “The Chief Veterinary Officer (CVO) has already written to the manufacturers asking them to give priority to pig and poultry processors”.
Mr McGowan also feared losing markets to imports.
Cabinet Secretary for Rural Affairs Fergus Ewing, who was on the Quality Meat Scotland stand at the Royal Highland Show to launch a new pork strategy, said he was aware of the problem and that it was ‘a key issue’ for his officials.
Poultry slaughterhouses were also affected with 50% to 60% of the sector using CO2 to stun birds and all companies use CO2 as part of the packaging process.
The absence of CO2 means many poultry producers will have to slow or halt their processes.
The British Poultry Council (BPC) said an inability to slaughter would mean birds remaining on farm.
It could also pose a risk to welfare which would have to be carefully managed in respect to requirements such as stocking density, which could be exceeded within two days.
A further impact may be on hatching of chicks with no farms to go to.
Decisions would have to be made as to removal of flocks/stock from the production process, which may mean on-farm slaughter.
BPC warned this risked not only immediate supplies of poultry but will mean a lengthier gap as flocks/farms have been taken out of the production cycle.
BPC Chief Executive, Richard Griffiths, called on the Government and major CO2 producers to prioritise slaughterhouses and ’keep the supply chain moving’.
“We are assessing what the possible impact on food supply might be, and BPC members are working hard to minimise the effect.
“It is worrying that failures in the gas sector can have such a potentially huge effect on British food production.
“The BPC will be working closely with Defra, BEIS, retailers, and gas suppliers to implement contingency plans and mitigate any major impact on sustainable supply of food.”
Beer production has also been hit.
Last week, reports said drinks giant Heineken’a John Smith’s Extra Smooth and Amstel products had already been impacted.
Holden’s beer bottling company in the West Midlands stopping production.
Others were more prepared with AB InBev, parent company of brands including Budweiser, Stella Artois and Corona stating it had CO2 recovery systems at both it breweries in the UK.
“They enable all CO2 from the brewing process to be recovered and sent back round the site.
“We do that because we are focused on sustainability and this is the best way to operate but it also means that we are largely self-sufficient.
“So currently our supply across both our breweries is good and we’re not anticipating any issue in the near future.”