**4. The regulation of SRM**

The contamination of animal carcass by SRM is not only a food and feed safety issue, but also of global economic importance, leading countries or areas such as the UK, the EU, Japan, Canada, and the USA to institute strict regulations to prevent SRM entering the human food/ animal feed chain (Table 2). Although SRM has different definitions in different countries and areas, bovine CNS tissue (brain and spinal cord) tops every list of prohibitive materials due to its high prion infectivity.


**Table 2.** Legislation related to prion disease control

Given that it was the first and most seriously area affected, it is not surprising that the early legislation to control the spread of prion diseases came from the UK. In 1995, the UK banned the use of MRM from bovine vertebral column for human consumption[82] and in 1996, the "over thirty months" rule came into force, which automatically banned older cattle from entering the human food chain.[83] In 1997, the UK enacted a comprehensive set of SRM regulations,[84] which classified SRM into specified sheep or goat material and specified bovine material. It also emphasized that no person should use or sell any SRM, or any food containing SRM, for human consumption. To further prevent SRM from entering the human food chain, the UK prohibited the practice of pithing in 2001.[85] The EU was also quick to take action; since the consumption of BSE-infected feedstuffs by ruminants was rapidly identified to be the main BSE transmission channel, in 1994 the EU banned the use of proteins originating from mammalian tissues for feeding ruminants.[86] Largely as a result of this feed ban, the UK's BSE risk status dropped from high to low between 1996 and 2012. Since 2013, the regulations have been relaxed somewhat and cattle aged over 72 months (O72M) are now permitted to enter the food chain if they have tested negative for BSE.[87]

In 2001, the World Health Organization recommended that all countries should introduce risk management procedures such as the identification and removal of entire bovine heads and/or prohibiting the harvesting of all MRM. All tissues that have been shown to be capable of carrying BSE infectivity should be removed and destroyed. If the risk is high, additional precautions should be taken such as prohibiting cattle over a certain age from entering the food chain.[88] The World Organization for Animal Health suggests that when countries import beef products from a BSE risk country or area, meat processing should not use airinjection stunning or pithing.[89]

In the EU, the use of air-injection stunning has been banned for slaughtering cattle since 2001; [90] it has also prohibited pithing since 2001.[65] In 1997, the EU enacted strict regulations prohibiting the use of SRM,[91] including the skull, brain, eyes, tonsils and spinal cord of cattle, sheep, and goats aged over 12 months and the spleens of sheep and goats. This was later extended to include bovine intestines in 2000[92] and vertebral columns in 2001.[93] Since 2000, all the member states of the EU, including the UK, are prohibited from producing MRM from bones of the head and vertebral columns of bovine, ovine, and caprine animals,[65] and this was extended to include all types of bones from these three species in 2001.[93] From 2001 onwards, SRM was excluded from the feed chain as a result of an EU-wide ban on the feeding of processed animal protein to all farmed animals.[94] In 2013, BSE testing in the EU has been changed to the O72M rule.[87]

Among the Asian countries, Japan has been the most severely affected by TSE, with about 36 cases of BSE and one case of vCJD being confirmed since 2001.[21, 95] In 2002, Japan announced that bovine MBM could not be used as an ingredient in animal feedstuffs and prohibited the use of specified materials from cattle.[96] However, the bovine vertebral column can still be consumed as food if it is derived from cattle originating from a BSE-free country or zone.[97] Because the BSE risk status has moderated somewhat, the age of cattle subject to inspection for BSE in Japan was revised upward from zero months to 21 months in 2005.[98] In 2013, it was further revised and is now only required for cattle over 48 months of age.[99]

In Canada, the first cases of BSE and vCJD were reported in 2003 and 2002, respectively, triggering a food directorate policy on SRM in the food supply that was implemented in 2003. [100] This required the removal of SRM from all cattle during the slaughtering process and prohibited its sale or import for human consumption.[101] The vertebral column from all cattle aged 30 months or older must now be removed as an inedible product and cannot be used in the preparation of MRM.[102] Canada has also prohibited the use of air-injection stunning and the pithing technique for cattle.[102]

The USA banned the use of proteins originating from ruminant tissues for feeding ruminants in 1997.[103] Later, the USA issued a prohibition of SRM consumption as food in January 2004, adopting a definition for SRM that is similar to that used in Canada.[104, 105] To ensure that AMRS do not become a means of spreading CNS tissue into meat products, the USA has also prohibited the use of brain, spinal cord, dorsal root ganglia, trigeminal ganglia, and significant amounts of bone solids or marrow of all cattle, as well as the skull and vertebral column of cattle 30 months of age and older, in AMRS.[106] The National Animal Identification System, an efficient and effective animal identification program, has been implemented in the USA since 2004 to support animal disease monitoring, surveillance, and eradication programs.[107] The USA has also prohibited the use of a number of cattle materials, including CNS-based SRM, in animal feedstuffs since 2009.[108] The USA currently prohibits the slaughter of cattle that are unable to stand or walk ("downer" cattle) when presented for pre-slaughter inspec‐ tion[109] and in January 2004 also banned air-injection stunning of cattle; pithing has never been used.[52] From January 2004 to May 2005, the USDA performed inspection and verifica‐ tion procedures in about 6,000 meat and poultry establishments and found 1,036 procedures (< 1%) that were not in compliance with the regulations related to SRM.[110] In 2008, about 1.5% of the US companies handling materials prohibited from use in ruminant feed (*n*=7,876) committed technical violations, mostly consisting of minor recordkeeping lapses or conditions involving non-ruminant feeds.[111] However, in January 2006, Japan suspended all US beef imports after discovering SRM in beef products exported from the USA.[112] In South Korea, US beef imports did not resume until June 26, 2008, after having been suspended in 2003 after the first BSE case was reported in the USA.[113]

Based on statistical information related to MBM,[114] it is clear that the problems with SRMcontaminated feed should not be forgotten. In 2000, the total amount of mammalian MBM produced in the USA was about three million metric tons.[115, 116] Ruminant tissues have been prohibited in ruminant feed in the USA to prevent the spread of BSE since 1997[103] and about 41,520 metric tons of animal feed in the USA were recalled between 2006 and 2007 due to the omission of the cautionary BSE statement on the label or as a result of ruminant MBM contamination during the feed processing procedure.[117] As the data shown in Table 1, it is very easy for meat products to become contaminated by bovine CNS-based SRM when the animal is slaughtered and during meat processing. In 2012, about 53% of the red meat produced in the USA. was beef,[118] but fewer than 1.2% of the cattle slaughtered are tested for BSE each year.[119, 120] As part of the regulation enforcement, about 65,693 metric tons of ruminant SRM-contaminated cattle products in the USA have been recalled since 2003.[121]
