The abattoir at Brechin was forced to stop processing pigs last week due to an EU-wide shortage of food-grade CO2.

Around 6,000 pigs a week are processed at the £10m facility which is run by Quality Pork Limited (QPL), a company formed by a collaboration between pig farmers and the major processor Tulip Ltd.

CO2 used in food manufacture is mainly a by-product of the production of ammonia for fertiliser. Ammonia production across Europe usually stops during the spring months and stocks of CO2 are then used to supply contracts. In the past year there has been a lower than average production of ammonia, and hence CO2, due to low prices.

A number of European fertiliser plants have closed for routine maintenance, while only two of the five UK plants are currently operating. That has lead to a serious shortage of CO2 in the EU, affecting a number of UK industries, including meat processing.

CO2 is used for a number of purposes within the meat supply chain - to stun pigs and poultry during the slaughter process, which is the most humane method available, and it is also mixed with nitrogen for use in packaging to help preserve products and extend shelf life.

There are approximately nine different grades of CO2, with food grade CO2 having 99.9 per cent purity. An interim risk assessment by Food Standards Scotland (FSS) has concluded that the food safety risk from the use of "non-food safety" CO2 to consumers is very low. FSS has therefore issued a derogation that CO2 at not less than 99 per cent purity can be used for the gas stunning of both pigs and poultry throughout the duration of the disruption to the normal food grade CO2 gas supplies in the UK. A similar temporary derogation has also been granted for the use of CO2 in Modified Atmosphere Packed (MAP) products.

Another temporary derogation for one week has been granted by Quality Meat Scotland (QMS), the red meat promotional body, so that QMS-assured Scottish pigs can be processed at the Tulip site in Ashton. That will allow pig-meat processed there to continue to carry the Specially Selected Pork logo.

These derogations will be of some help until normal slaughtering resumes, but in the meantime there is still a bit of slack on Scottish farms to hold pigs for a while with makeshift arrangements as the backlog is slaughtered.

This incident has highlighted how vulnerable intensive livestock systems are to any loss of slaughtering capacity. If pigs are not slaughtered on time they can become too big and fat for market requirements, and pig accommodation can become overcrowded leading to welfare issues.

Another concern is that if retailers can't source Scottish pork, they will switch to imported product and once they do that it is often not for a week, but for a month.

Poultry producers face much the same problems.

A high proportion of the British poultry meat sector (50 - 60 per cent) uses CO2 to stun birds as part of the slaughter process, and all companies use CO2 as part of the packaging process to improve shelf life.

The absence of CO2 could lead to poultry producers having to slow or halt their processes. If birds cannot be stunned they cannot be slaughtered. The inability to slaughter birds has a direct impact on the supply of food, both in quantity and consistency of supply.

Looking backwards down the production chain, an inability to slaughter leaves birds remaining on farms. In this scenario their welfare would have to be carefully managed with regard to requirements such as stocking density, which could be exceeded within a few days - modern commercial broiler chicks grow fast with most reaching slaughter weight between 4 and 7 weeks of age.

A further impact may be on hatching chicks. With no farms to go to, they may have to be put down. Decisions would also have to be made as to removal of flocks/birds from the production process, which may mean on-farm slaughter.

As with the pig industry, where possible, poultry abattoirs have backup slaughter options, but currently these are not capable of maintaining the volume of production for a significant length of time and are only intended as temporary options. Businesses can also divert gas away from packaging to stunning, but this option also cannot sustain production for more than a few days.

Lessons need to be learned from this incident. All producers and processors of intensive livestock need to critically examine their systems to identify potential risks so they can develop effective contingency plans.