In 2010 the TSE Roadmap II stated that potential partial relaxation of the total feed ban had to be based on a stepwise approach supported by scientific evidences. In this respect improvement of existing methods as well as the development of new ones are crucial for supporting any future amendment while still monitoring the potential re-emergence of BSE.
EURL-AP research activity in this area, in close collaboration with the NRLs, primarily focussed on:
- The improvement of the current methods
- Innovative combinations of methods with a view to the implementation of a future species-to-species feed ban
Combination of methods
“No method tells the whole truth.”
Regardless of whether analyses are carried out by light microscopy, by PCR, by NIRM or by screening methods such as immunoassays, none of the used method shall deliver the entire information necessary for a species-to-species feed ban. Therefore combination of methods – principally light microscopy and PCR as these are the most successful ones – is required. Such combination is mandatory for aquafeed analysis since 16th of January 2013.
Some few illustrations…
- In 2013 non-ruminant PAPs were authorised again in aquafeed. According to TSE Roadmap II, porcine PAPs could also be introduced in the future to poultry feed. Light microscopic analysis of such poultry feed containing porcine PAPs will reveal only the presence of terrestrial PAPs but will be unable to inform on the species of origin of the PAP used. Complementary information by PCR would indicate the porcine nature of the PAP. Furthermore PCR shall also reveal the presence or absence of prohibited poultry material which is prohibited to prevent intraspecific recycling.
In this first example, the use of animal by-products is limited to one ingredient. The situation becomes more complex if several feed materials of animal origin are included in a compound feed.
- The case of an aquafeed containing non-ruminant PAPs (e.g. porcine PAPs), non-ruminant blood products (e.g. porcine haemoglobin powder) AND dairy product (e.g. casein) is a good illustration. All these ingredients are authorised in aquafeed. Light microscopic analysis of this kind of feed will of course detect terrestrial PAPs. PCR analysis will logically be positive for ruminant target due to the presence of dairy product containing ruminant DNA. Complementary PCR analyses would also detect porcine DNA. Nevertheless, same results would be obtained for a feed containing prohibited ruminant PAPs instead of non-ruminant PAPs. In this case, the use of authorised by-products (e.g. dairy products) will hide banned by-products. MS-based proteomics is able to distinguish these two scenarios by the specific identification of prohibited proteins of ruminant origin,
Whether or not a combination of analytical methods is required would probably depend on the type of feed. It is certainly not justified for every feed type as in the next example.
- Dairy by-products are authorized in bovine feed. PCR performed on such feed shall react positively to a bovine or ruminant target, but shall not succeed in delivering information on the nature of the ingredient responsible for the signal. A second line light microscopic analysis on this feed will help to certify the absence of prohibited material as PAPs –as no bones, no cartilage and no muscles will be found. The feed can therefore be declared as fit for its purpose.
In the previous example, light microscopic analysis would have been performed first without even the need for a complementary PCR test. Such option would spare time and finances.
- Sometimes official reports mention the presence of terrestrial material detected by light microscopy in fish meals. PCR tests shall in the future be able to confirm that this material originates from unintentional sea mammals by-catch instead of real terrestrial animals. In addition, as recently re-authorized, fish feed may aside fish meal as well contain terrestrial PAPs on the exclusion of ruminant ones. In case of absence of information related to the composition, a first test by light microscopy shall disclose the presence of terrestrial PAPs whereas a successive PCR testing will ascertain that those PAPs do not originate from ruminants hence enabling to declare the fish feed as fit for its utilization.