Alternative procedures for efficient detection of Caseous Lymphadenitis (CLA) lesions in sheep and goats at slaughter

Summary

​Post mortem inspection of sheep and cattle in abattoirs is an integral part of quality assurance in the Australian red meat industry. A criticism of meat inspection in all developed countries, including Australia, is that resources are not directed at issues posing the greatest risk to product safety. Following an initial workshop with key industry stakeholders to develop the R&D and adoption strategy for post-mortem inspection a number of projects were conducted.

Historical review

An external review was completed with the aim of providing a sound scientific basis for increasing the efficiency and effectiveness of post-mortem inspections in abattoirs, while maintaining control over the safety of product and its suitability for consumers.

Malignant neoplasia

The occurrence of malignant neoplasia in adult cattle at slaughter is the "leading cause of condemnation of the carcases of adult cattle". However, very little is known about the management of this issue and the diagnostic accuracy of the inspection process. Greater knowledge surrounding this area will potentially result in reduced condemnations and improved management of affected carcases.

Enhanced accuracy surrounding disposition subsequent to diagnosis of malignant neoplasia is important in order to optimize both economic return from the slaughter process, and to protect consumer public health and/or public health perception.

A review of the literature has found studies focusing on particular types of neoplasia and their associated characteristics. Research investigating the characteristics of lesions in adult cattle at slaughter and the decision process leading to a disposition in Australia is currently not well represented in the literature.

The project consists of two parts, the aims of which, as outlined in the Terms of reference, are outlined below:

• Part A - Gross characteristics
  The aim of this part of the project was to define the frequency and gross characteristics of various neoplasms causing condemnation of tissues or carcases at Australian export abattoirs (excluding ocular SCC).
• Part B - Histological characteristics
  The aim of Part B was to characterise the histological attributes of lesions identified by meat inspection as malignant neoplasia ("tumours" using the AS terminology) in the carcases of adult cattle at Australian export abattoirs (excluding ocular SCC).
  Review of post-mortem inspection and disposition schedules of the Australian standard

A review utilising Codex Alimentarius risk assessment methodology, was conducted with the aim of identifying:

• removing procedures that are no longer necessary due to the improving animal health status of the Australian herd;
• altering or removing procedures where new knowledge of animal or foodborne disease indicates current risk management procedures are not effective;
• using alternate risk management procedures either at the processor or elsewhere in the supply chain; and
• transferring where possible, procedures that are principally related to product quality rather than food safety to companies' Quality Assurance (QA) systems.

Cysticercus bovis

A sensitive and specific probe-based molecular assay has been developed and evaluated to improve detection of bovine cysticercosis caused by Taenia saginata in slaughtered Australian beef cattle. Two real-time PCR approaches, including a SYBR green dye and Taqman MGB hybridisation probe assay, were compared for their diagnostic utility. The Taqman MGB probe assay was selected for further test performance and validation studies based on its fast turnaround time, ease of interpretation and high levels of specificity and sensitivity.

Tuberculosis

Australia declared freedom from bovine tuberculosis in accordance with international guidelines in 1997 and has since maintained ongoing surveillance for this disease, primarily through abattoir surveillance of cattle carcasses (meat inspection) for tuberculosis-like granulomas. The objectives of this study were to estimate the sensitivity of Australia's surveillance system and quantify the probability that Australia is free from bovine tuberculosis at the specified design prevalence.

The analysis included approximately 80 million records of individual cattle slaughtered and meat inspected at Australian abattoirs between 2005 and 2015 calendar years. Animals were identified and aggregated by property of birth within year. Herd and population-level sensitivities and probability of freedom were estimated on an annual basis using a simulation model to account for uncertainty about the unit sensitivity of the meat inspection process. The estimated median population sensitivity of Australia's tuberculosis surveillance system varied from a high of 80% in years when traditional meat inspection was used to as low as 50% after the introduction of visual-only meat inspection, for a design prevalence of 0.01% (19 herds) of Australian breeding cattle herds and 0.5% of animals within infected herds. The level of confidence in Australia's freedom from bovine TB was >95% after the first year of the analysis and >99.5% from 2007 through to the end of the analysis period in 2015. Reducing the animal-level or herd-level design prevalence reduced system sensitivity but the confidence of disease freedom remained high.

Data collection

It is recognised that collection of data at, and around, post-mortem inspection, could provide data for further risk assessment, as well as having value to feedback to farms for the purpose of improving animal husbandry, and carcase yield. A preliminary data collection standard was developed; the project was terminated in favour of the Rural R&D for Profit project, Health 4 Wealth, which will continue the development.