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Trial of Visual Inspection of Fattening Pigs from Non-controlled Housing Conditions

25 June 2013

A visual inspection system of pig carcasses from outdoor or non-controlled housing systems would face the same obstacles for implementation as a visual system for fattening pigs from controlled housing conditions, according to a new study.

This was the conclusion of a study carried out by the Scottish Agricultural College for the Food Standards Agency in the UK.

The research team of Sue Tongue, Ruth Abascal, Judith Evans, Catriona Webster and Carla Gomes from the Epidemiology Research Unit at Future Farming Systems SRUC Research and Ian McCrone from the University of Cambridge said that as visual inspection is acceptable for indoor pigs from controlled housing conditions, there is no public health reason to exclude fattening pigs from outdoor, non-controlled housing conditions purely on grounds of the management system from which they originate.

The study says that the purpose of meat inspection is to contribute to the production of safe food for human consumption and derogations from European Union (EU) regulations enable carcasses of fattening pigs to be inspected by visual-only methods, provided that certain requirements are met, and the pigs have been reared under controlled housing conditions, in integrated production systems, from weaning to slaughter.

Such visual-only methods reduce the handling of the carcasses or incisions into parts of it by the meat inspectors, which may reduce the risk of cross-carcass contamination.

However, the uptake of visual-only inspection by the pig industry in the UK has been low because slaughterhouses accept a mixture of indoor and outdoor reared pigs throughout the day and the outdoor housed pigs still need to be inspected by traditional means.

In the study, entitled 'Trial of visual inspection of fattening pigs from non-controlled housing conditions', the researchers looked at carcasses from pigs reared in outdoor management systems from weaning to slaughter.

“As far as we are aware, all such pigs in the UK are also born in outdoor management systems,” the research team said.

The project consisted of a field study, which investigated the frequency and types of conditions that could be identified by the two different meat inspection methods when fattening pigs from outdoor housing conditions were slaughtered in an abattoir in the UK.

The two different meat inspection methods used were the 'traditional' method and a 'visual-only' method.

The traditional method involved visual inspection with additional handling and incisions to investigate parts of the carcass and offal (the internal organs and entrails) that cannot be easily observed from the outside.

With the visual-only method, no handling of the carcass and offal was allowed.

“We compared the conditions that could be found by each inspection method. We also took samples, after each inspection method, from a subset of the carcasss to see if we could grow particular bacteria,” the research team said.

“These bacteria are either indicators for the hygiene of the slaughter process (total aerobic and Enterobacteriaceae counts), or can cause food-borne disease in humans (Salmonella spp. and Yersinia spp.).

“We compared whether they were present or absent and how many could be found on the carcasses after each inspection method.”

The study then used the results from the field study along with previous work, scientific literature and publicly available information to do a formal, mostly qualitative, risk assessment (RA), based on guidelines described by the Codex Alimentarius Commission (CAC).

The risks to public health, animal health and animal welfare and whether these risks would change if visual-only inspection for fattening pigs from non-controlled housing conditions was to be introduced were examined.

In addition, obstacles there might be to the implementation of visual-only inspection for fattening pigs in UK abattoirs were also explored.

The research looked at historical records about the meat inspection practices at the abattoir with information about ante- and post-mortem inspection of more than 1.2 million pigs from both indoor and outdoor housing systems. Batch size and seasonality were also taken into account when examining the prevalence of disease or abnormalities in the carcasses.

The mean or average prevalence in batches with each condition was also compared between the two management systems.

The results showed that the prevalence of conditions detected on inspection of pigs submitted to slaughter from different fattening systems were quite similar.

Most of the differences found were predictable from knowledge of the housing and fattening systems being used and the relationship with the diseases, or circumstances from which the conditions arose.

In the field study, more than 11,000 carcasses of fattening pigs from non-controlled housing conditions from 62 batches and 12 farms were inspected.

Every carcass was inspected using both post-mortem inspection method (traditional and visual-only inspection).

The number of carcasses affected by each condition was recorded at a batch level for each inspection method.

There were statistically significant differences in the frequencies found by the two inspection methods for six of the categories of conditions. However, the biological differences (i.e. what the numbers meant in terms of actual carcasses or conditions missed/found) were very small.

The frequencies were higher with the visual method of detection for hair contamination which was explained by the early position of the visual-only inspection on the line.

The frequencies were higher with the traditional method of inspection for milk spot, renal pathology, enteritis, pluck pathology and faecal contamination.

Samples for microbiological investigation were taken after visual-only inspection and after traditional inspection.

Swabs were taken for Enterobacteriaceae count and Salmonella spp. isolation.

No Salmonella spp. were isolated from any sample in the study. Also no statistical difference was found in the proportion of carcasses contaminated with Yersinia spp. after the two inspection methods.

Although there was no evidence for a difference in the general bacterial contamination of carcasses after the two inspection methods, when carcasses were examined where Enterobacteriaceae were present, there was some evidence that the level of contamination of carcasses was lower after visual-only inspection than traditional inspection.

“We concluded that there was some evidence for a reduction in the cross-contamination of carcasses by changing the post-mortem inspection method to a visual-only system where handling of carcasses by FSA personnel was minimised,” the researchers said.

Because the result had been observed in a particularly clean abattoir, the team said that a similar outcome would be expected to be observed in any abattoir with level of contamination as low as and higher than the study premises.

The potential for a change in risk to human health via a food-borne route, animal health and animal welfare if the meat inspection method was changed from the traditional method to a visual-only method was also assessed.

The researchers said that visual inspection is acceptable for indoor pigs from controlled housing conditions and there is no reason relevant to the public health risk presented to exclude fattening pigs from outdoor, non-controlled housing conditions purely on grounds of the management system from which they originate.

They said that there is also no reason for the exclusion of such pigs from a visual inspection system due to the revised risk to animal health.

They said that it is possible that a change in the inspection method from traditional to visual would lead to reduced microbial contamination of carcasses in any abattoir with a level of contamination as low as or higher than the study premises.

“If the level of contamination of carcasses is reduced by a change in inspection method, then it could be hypothesised that the potential for cross-contamination would be also be reduced; however, we cannot draw that as a conclusion from our study,” the team said.

“We conclude that the major obstacles to implementation of a visual-only system of inspection that encompassed pigs from non-controlled housing conditions ('outdoor') in the UK would be the same as those that are expected if visual-only inspection were to be implemented for fattening pigs from controlled housing conditions.”

Further Reading

You can view the full report by clicking here.

June 2013

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