Detection of meat and bone meal in cattle feed and ruminal fluid – Comparison and combining of microscopy and polymerase chain reaction

The ban of processed animal proteins (PAP) in feed for farmed animals led to a significant reduction of the number of BSE cases ever since bovine spongiform encephalopathy (BSE) was proven to be a “feedborne” disease. Although optical microscopy has been the only reference method for the detection of PAP for years, the EU legislation also foresees that other methods may be applied in addition to the microscopy, if they provide appropriate information about the origin of the animal constituents present in animal feed. This was set to become a reality in the European Union from the 1st of June 2013 when meat and bone meal (MBM) was reintroduced in fish feed. This paper presents a comparison and the possibility of combining classical microscopy and conventional polymerase chain reaction (PCR), as complementary techniques, implemented to detect the presence of fish meal and bovine, poultry, pig and mixed MBM in cattle feed. Both methods were also applied on the samples of ruminal fluid of cows fed feed containing MBM. The ruminal fluid was chosen to be tested in order to determine its forensic significance, as it is often not possible to perform the analysis of the incrimiated feed that has already been consumed. In contrast to the high sensitivity of microscopy, the results obtained by PCR showed substantial variability, even when applied to the isolated bones. Particles of animal origin in ruminal fluid were detected only by microscopy.