BSE controls final report, 20 December 2000, section 9, The controls: The Over Thirty Month (OTM) Rule
33.Controls for both live animals and meat have been introduced and strengthened since the late 1980s to limit the exposure of humans to infected meat and of animals to infected feed so as to reduce as far as possible the size of the epidemic. Apart from the continuing requirement that suspected cases of BSE and the offspring of confirmed cases are notified and destroyed, the two principal controls to keep infected material out of the food chain are the Over Thirty Month Rule (OTM Rule) and the removal of parts of the body that carry the highest demonstrable levels of infection (Specified Risk Material (SRM)). The principal control to prevent infectivity re-entering cattle and to reduce the incidence of BSE is the ban on feeding mammalian MBM to any farmed livestock. These controls are inextricably linked, in that any relaxation in one would affect decisions about whether the others could be altered. Whilst enforcement of the controls is given very high priority it can, of course, never be completely effective.
The Over Thirty Month (OTM) Rule
34.With two exceptions26, beef from cattle aged over thirty months at slaughter is banned from sale for human consumption in the UK. The rule is designed to reduce human exposure to the BSE agent. It was introduced in 1996 following SEAC advice that meat from these older cattle should be deboned under official supervision in licensed cutting plants, before sale. This proved to be impractical due to lack of cutting capacity for this volume of meat and insufficient numbers of official inspectors to undertake the supervision. Instead a pragmatic solution of excluding older cattle from the food chain was adopted.
35.The 30 month limit was chosen for a number of reasons. First, very few animals had shown signs of BSE onset at this age. In the two years before the Committee's recommendation in 1996 there had been only three clinically identified cases of BSE in cattle aged 30 months or younger. Second, data from experimental studies of the pathogenesis of scrapie in rodents had shown that infectivity was first detected in the central nervous system approximately half way through the incubation period. The mean age when signs appear in cattle is approximately 60 months, therefore 30 months should by analogy be a time at which infectivity is just emerging. Third, the earliest appearance of signs in cattle following experimental feeding with infected material is about 32 to 33 months. The OTM rule is enforced in abattoirs by the Meat Hygiene Service physically checking each animal's teeth at slaughter, backed up by documentary evidence of its age (see also paragraph 42). In Northern Ireland the documentary evidence is backed up by the tooth check where necessary. The rule is enforced in abattoirs there by the Department of Agriculture and Rural Development (DARD). The tooth check (that no more than two permanent incisor teeth are erupted through the gum) has been a convenient, if imprecise, measure since in cattle the second pair of incisors erupt at approximately 27 months.
36.No BSE cases in cattle aged 30 months or under have been diagnosed since 1997. A total of 84 confirmed cases estimated to be aged 30 months or under occurred before 1997 (due to uncertainty of some birth dates, 46 are known and 38 are estimated). The youngest ages at diagnosis since 1997 have been: 1997 - 37 months, 1998 - 34 months, 1999 – 39 months and 2000 – 42 months. In experiments in which cattle were fed on substantial doses of BSE-infected cattle brain, evidence of infectivity was sought (by inoculating material into mice) in a wide range of tissues throughout the incubation period and after clinical onset of disease. Infection was found in parts of the small intestine at several time points (from 6 to 18 months post challenge) in the incubation period, at a late stage (38 months post challenge) in bone marrow (on one occasion only) and in central nervous system tissues (at around the period of clinical onset). No evidence of infection was found in muscle meat in these studies, nor has it been found in the muscle of cattle clinically affected with the natural disease. Experiments with mice are inherently insensitive because they involve the species barrier. The most sensitive test would be to feed the material to cattle or to inject it into cattle brains. A table of experiments carried out is at Annex H. This table shows that some of the most sensitive tests (cattle to cattle) have been carried out on small numbers of animals or have not been carried out at all. However, on the basis of work done so far, the OTM rule (combined with removal of SRM) does keep known infective tissues out of the food chain.
37.Animals born after 1 August 1996 should not have been exposed to BSE infectivity through contaminated feed (see paragraph 56.) They are, of course, becoming an ever-increasing proportion of the national herd. Since the average incubation period for BSE in cattle is about 5 years it will be mid 2001 before we will know whether the strengthened feed ban has had its intended effect. The case born since 1 August 1996 could have been due to maternal transmission, which is estimated27 to occur in up to 10% of pregnancies where the dam was showing signs of BSE or where the dam was within 6 months of showing signs. The MAFF enquiry into the cause of the case concluded that it is not possible to establish how the animal contracted BSE.28
38.Controls on the identification and tracing of cattle have been gradually increased in the last few years. All cattle born in Great Britain since 1 July 1996 are now required to have passports, with those born since 28 September 1998 being subject to computerised recording of movements under the Cattle Tracing System (CTS). A project to add all the remaining cattle to the database is nearing completion. In Northern Ireland a fully computerised database (the Animal and Public Health Information System – "APHIS") is in place instead. Checks on farms in Great Britain show that there are discrepancies in about 9% of cattle inspected, including identification, documentation and poor record keeping29. From 30 October 2000, Agriculture Departments have been routinely imposing sanctions which involve individual and whole herd movement restrictions with compulsory slaughter of unidentified animals where appropriate. A strategy for educating farmers is being developed with the help of the industry. Nevertheless, the need for continuing physical checks of teeth at the slaughterhouse remains. We recommend that relevant passport discrepancies are reduced to as close to zero as possible.
39. The cost of the introduction of the OTM rule has been substantial. Cattle too old for entry into the human food chain are almost all disposed of through the Over Thirty Month Scheme (OTMS) under which farmers are paid compensation by the Government for their unsaleable animals30. Since 1996 nearly 4.7 million cattle have been slaughtered under the scheme at a cost of over £1.5 billion in compensation. In addition, the Government is also responsible for costs of disposal of carcases by incineration or rendering followed by incineration of the resulting MBM and tallow. The cost of disposal, as at 31 March 2000, has amounted to over £575 million since 1996. The current annual overall cost to the Government, including compensation, is nearly £400 million31. Up to 70% of the compensation costs are eligible for reimbursement from the European Union but only once all the material has been completely destroyed. Because of the effect of the Fontainebleau rebate mechanism, even the compensation costs are in practice funded mainly by the UK Exchequer. In addition, the National Farmers’ Union has estimated that the cost to industry of the OTM rule is about £95 million a year32.
40. There are, of course, benefits as well as costs from the Scheme, though these are much more difficult, if not impossible, to quantify. The principal benefit is the protection of humans from exposure to BSE. A survey of 3950 OTMS (5 years and older) cattle brains carried out in 1999 found 0.4% to have histopathological signs of BSE. It has been estimated33 that the number of BSE infected cattle under 30 months which could enter the human food chain and which would develop clinical disease within 12 months if they were not slaughtered is only 1.2 across Great Britain as a whole in 2000 (with a range of 0 to 4 cattle). It would appear, therefore, that at present the OTM rule is removing from the food chain at least 99.9%34 of cattle close to developing BSE. Existence of the OTM rule is thus likely to enhance consumer confidence.
41.In addition to removing clinically normal cattle that are close to developing symptoms of BSE from the human food chain, the OTM rule has also prevented over thirty month old casualty cattle from being slaughtered for human consumption. Prior to 1996 the carcases of such cattle, which had been slaughtered on farm, could be taken into slaughterhouses if accompanied by veterinary certification stating that that they were not affected by a disease which would render the whole carcase unfit. The likelihood that some such animals may have been affected by BSE, but were not showing typical signs, is supported by Swiss work35 which found a higher incidence of BSE post mortem in casualty cattle than in routinely slaughtered cattle.
42. As noted in paragraph 35 above, the OTM rule is enforced in abattoirs by the Meat Hygiene Service. Although records of cattle rejected under the rule are kept at individual abattoirs, these are not collated centrally by the MHS. Equivalent Northern Ireland figures are collected by DARD. We recommend that in future this should be done by the MHS, and the details published.
43.The OTM rule is precautionary but was introduced in the context of great uncertainty. In order to protect the public from additional risk we will have to ensure, before relaxing or phasing out the OTM rule, that:
(i)the BSE epidemic is declining as currently forecast; and
(ii)the number of BSE cases in cattle born after 1 August 1996 is in line with predicted levels; and
(iii)we have evidence of comprehensive and reliable cattle identification procedures which apply to all animals and which are robustly enforced and subject to independent evaluation; and
(iv)the feed ban continues to be rigorously enforced.
44. If these conditions are satisfied, it should be possible to phase out the OTM rule, with a view to its eventual abolition. In view of the studies mentioned in paragraph 35 above and the problems with cattle passports (see paragraph 38), we recommend that 30 months should remain the age at which controls are most appropriate. It would be safer to relate any change in controls to a specific date after which cattle were born rather than embark upon an incremental increase in the age at which cattle may be slaughtered for human consumption. Changes might be considered differentially by geographical area in the light of different levels of BSE incidence (see Table 2 below). However, practical difficulties might be created because of normal commercial movement of animals. TABLE 2 BSE Cases
| Northern Ireland | Scotland | England | Wales | Republic of Ireland | France | |
|---|---|---|---|---|---|---|
| BSE cases November 1999 to October 2000 | 16 | 37 | 1,424 | 118 | 116 | 91 |
| Cattle population (million) | 1.8 | 2.1 | 6.4 | 1.1 | 7 | 21 |
| Number of cattle more than 24 months old (million) | 0.7 | 0.9 | 3.2 | 0.6 | 3.5 | 11 |
| BSE cases per milion cattle over 24 months old | 21.8 | 42.1 | 448.8 | 187.4 | 33.8 | 8.3 |
45. An alternative approach would be to test every animal at slaughter. This is now being introduced by the European Commission for every OTM animal going into the food chain. But the implementation of large scale testing raises unresolved questions about the practicalities of using the current diagnostic tests on a commercial scale in the abattoir. Furthermore, the current tests are limited in their sensitivity to preclinical BSE. They will therefore provide less consumer protection than the OTM rule. We recommend that the practicality and sensitivity issues are considered by SEAC.
46. We recommend that January 2002 is the earliest date on which a decision could be taken to announce the year of birth of animals that need not enter the OTMS (this could not be earlier than August 1996 when the enhanced feed ban was introduced). This would allow time for a review in August 2001 of the effectiveness of the tightened feed controls introduced in August 1996 and of evidence of BSE incidence five years after that time. Projections36 provided for this review suggest that 2003 is the earliest date that the rule could be removed altogether without increasing the current risk. Any relaxation of the OTM rule should be accompanied by a tightening of the rules which allow carcases of casualty animals to enter slaughterhouses to be dressed for human consumption, to prevent animals, other than those which have been injured or have discrete local lesions, from entering the human food chain. Relaxation will also depend on the continued application and effective enforcement of the SRM rules.
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26 - The first exception relates to very low BSE risk cattle from a small number of specialist beef herds registered under the Beef Assurance Scheme which may be slaughtered for sale for human consumption up to 42 months. The second relates to imports from 14 traditional suppliers of the UK market (Argentina, Australia, Botswana, Brazil, Mauritius, Namibia, New Zealand, Paraguay, Poland, South Africa, Swaziland, Uruguay, the United States of America and Zimbabwe) which were exempted when the rule was introduced.
27 - Donnelly CA et al, Analysis of the bovine spongiform encephalopathy maternal cohort study: evidence of direct maternal transmission, Applied Statistics 46, 321-344, (1997) and Donnelly CA et al, Analysis of the dam-calf pairs of BSE cases: confirmation of maternal risk enhancement. Proceedings of the Royal Society London B264, 1647-1656, 1997
28 - http://www.defra.gov.uk/animalh/bse/publichealth/index.html.
29 - Advice to the Government from the Chief Medical Officer, 30 July 1999.
30 - Any that are not put through the Scheme do not go into the food chain but are disposed of without compensation as high risk animal by-products under the Animal By-products Order 1999 (SI 1999/646).
31 - Departmental Report 2000 by the Ministry of Agriculture, Fisheries and Food, the Intervention Board and the Forestry Commission (April 2000, Cmnd 4612)
32 - Letter to Review Secretariat from NFU, 19 October 2000. The estimate is based on the difference between the amount of OTMS compensation received and the trend in the level of market prices across the EU which the NFU has assumed would have been followed in the UK under normal market conditions.
33 - Donnelly CA et al, University of Oxford, Estimates provided to SEAC in November 1999.
34 - Calculated on the basis that the OTM rule will remove one million cattle from the food chain this year, of which 0.4% (4,000) will have been close to exhibiting clinical signs and no more than 4 cattle slaughtered for human consumption will be within 12 months of developing clinical signs.
35 - Doherr M et al, Targeted surveillance for bovine spongiform encephalopathy, Veterinary Record, 145, 672 (1999)
36 - Analysis by Ferguson NM et al, Dept of Infectious Disease Epidemiology, Imperial College, London.