Head meat contamination

Results:

The commercially available Ridascreen® Risk material 10/5 test kit, sold by R-Biopharm Ltd, was selected for use in this project. A comprehensive validation of this kit was performed, which included optimisation of the kit parameters to produce reliable and reproducible data, correlation of % CNS tissue to concentration of glial fibrillary acidic protein (GFAP), calibration using a traceable source of GFAP and accurate estimation of the limit of detection. Brain stem homogenates were used for quality assurance purposes to establish good and reproducible recoveries of added CNS material. To date, this has not been done in a quantitative manner by other workers in this field. Data produced in the validation of the kit showed that the optimised R-Biopharm kit was:

• Traceable to a GFAP standard of known purity and provenance; work can potentially be reproduced by any analyst.
• Able to produce results as concentrations of GFAP, which can be converted to any CNS tissue type.
• Capable of producing reliable and quantitative data to allow comparisons between different abattoir practices.
• Capable of detecting concentrations of GFAP equivalent to a little as 1 μg brain tissue.

To accompany the optimised R-Biopharm kit for the determination of CNS tissue, a swabbing protocol for use in busy abattoirs was developed. This involved the investigation and optimisation of swab type, swab area, swabbing medium, number of swabs to take, successive extractions, swab equilibration period and swab stability. The developed swabbing protocol was successfully tested in this project and it has been shown that it can be easily transferred for use on a busy abattoir processing line.

A comprehensive assessment of current industry practice was conducted, which revealed that wide range of practices are in use for the removal and handling of head meat. Information was collected on all aspects of slaughter and dressing considered to be have the potential to influence contamination of head meat with CNS material, and details of head meat harvesting procedures including:

• stunning method;
• bunging of cranial bolt hole;
• head skinning method (manual or by hide puller);
• brain stem sampling point (before or after head meat removal);
• method of moving heads to harvesting location;
• harvesting of head material and processes used.

Variations in practice in these four main areas were used to construct two scenarios based on hypothetical risk of contamination (high and low) and were studied in two abattoirs with very different operating practices. In addition, the GFAP load on head meat samples after different handling and harvesting methods were studied, including storage, transport and unloading of heads to mimic best practise movement of heads from an abattoir to a cutting plant‘. The results obtained demonstrate that:

• CNS tissue contamination of head meat does occur during normal processing of carcases at abattoirs and the marker protein GFAP can be detected on some heads.
• Washing heads decreased the CNS tissue contamination on heads.
• Trimming decreased the CNS tissue surface contamination of harvested cheek meat.
• There is a reduction in CNS tissue contamination if bungs are inserted in the shooting hole; Bunging the foramen magnum does not appear to offer any additional benefit.
• Brain stem sampling does not increase CNS tissue contamination of cheeks on heads on the kill line.
• Brain stem sampling does increase CNS tissue contamination of harvested cheek meat, albeit by comparison with control samples that were from a different day, but the concentrations of GFAP determined fell within the range for samples harvested under normal‘ abattoir conditions.
• Contamination of cutting boards can occur.
• Overnight refrigerated storage of heads on A frames does not increase CNS tissue contamination.
• The CNS tissue load on head meat harvested on-line was not significantly different to chilled head meat that had been transported on A frames from the abattoir to a cutting plant‘ and unloaded.
• The CNS tissue load of cheek meat harvested on-line‘ (highest median results obtained 0.015 mg of brain tissue) is similar to retail samples of cheek meat (shown to contain the equivalent of 0.022 mg of brain tissue).

The project has shown that CNS contamination of head meat does occur during normal processing of carcases at abattoirs and that the marker protein GFAP can be detected on some heads. Not using bungs in the shooting hole significantly increased the CNS contamination of head meat on the line. Brain stem sampling does not increase the contamination of CNS material of cheek meat on heads on the kill line. For harvested cheek meat, however, brain stem sampling does increase the contamination of CNS material but the concentrations obtained were not significant when compared to the results obtained for the normal‘ processing of heads. None of the other processes studied; storage and, transport and unloading increased the amount of CNS contamination of heads and head meat from cattle slaughtered in UK abattoirs.

The project has been successful in fulfilling its aim of providing a scientific basis for an assessment of the movement of heads and the consequences for public health risk from the consumption of cheek meat harvested from heads transported, using best practice, to cutting plants.

Planned activity:

None.  We were subcontractors in this project.

The Problem:

Prior to May 2006, bovine heads from animals aged over twelve months were classified as SRM in the UK but this was revoked when the beef export ban was lifted and the same regulations were applied to all EU member states. However, there is no information on the prevalence or amount of CNS contamination of heads and head meat from cattle slaughtered in UK abattoirs and therefore no basis for an assessment of public health risk from these sources should a slaughtered animal be carrying the BSE infectious agent. There are many factors that have potential to introduce substantial variability in the degree of contamination of head meat, including abattoir practices and subsequent moving and storage of heads if harvesting meat is performed off-line or in separate premises.  Currently head meat can only be removed in the abattoir but there is the potential to allow head meat to be removed in licensed cutting plants.  The data generated in this study will help inform decisions on future guidelines.

Project Aims:

1. To obtain information on industry practice and variation in methods of processing bovine heads
2. To construct protocols for sampling heads and head meat in abattoirs for CNS material, and the laboratory determination and quantification of CNS indicator proteins
3. To determine the CNS contamination of head meat after harvesting according to the different methods identified

Approach:

A comprehensive evaluation of the contamination of bovine heads and head meat by CNS material will be based on current industry practices and on a simulation of procedures that would be used if heads were processed at cutting plants. Contamination will be quantified using CNS marker protein(s) and will be measured on head meat after different handling and harvesting methods.