(Introduction)

Animal Health Bill

Impact on breeds of sheep with a genotype susceptible to scrapie

 

Information document prepared by:

 

 

Northern Short-Tailed Sheep Group

 

with support from

 

 

Rare Breeds International

 

Traditional Livestock Foundation

 

 

27 December 2001

 

 

 

Executive Summary

 

7        The policy of mass slaughter applied as the preferred method for the control of FMD/2001 in UK has resulted in the population of native breeds of special genetic importance (as defined by Rare Breeds International) being reduced by up to 50%.

 

7        The Animal Health Bill gives the Government even greater powers to slaughter livestock, to the extent that it undermines principles of civil liberties.

 

7        Application of the powers proposed by the Animal Health Bill is not restricted to FMD control. It extends to other diseases and could lead to the extinction of some native breeds of special genetic importance when applied to selection for the ARR scrapie-resistant' allele in sheep.

 

7        Rare Breeds International recognises 31 native breeds of sheep of special genetic importance in UK, and at least 9 of these would be at serious risk because of their low frequency of the ARR allele.

 

7        The genetics and science of the prion protein are not properly understood, and the application of measures proposed by the Animal Health Bill are unacceptable in the context of current knowledge. Political expediency is ignoring unsafe and bad science.

 

7        Scrapie has not been shown to have adverse effects on human health.

BSE has not been found to occur naturally in sheep.

It is not proven that BSE is the cause of vCJD.

 

7        Further research must be carried out to increase the understanding of the prion protein and the inter-relationship of TSEs before irrevocable steps are taken which may lead to the extinction of some native breeds. Breeds particularly at risk include the genetically-distinct Northern Short-Tailed group of breeds, the high-performance Marsh breeds, and the environmentally-important Mountain breeds.

 

7        The Animal Health Bill refers to exemption from slaughter in exceptional circumstances' but these are not defined.

 

7        DEFRA should recognise the list of breeds published by Rare Breeds International and should make specific policy for these breeds.

 

7        The Animal Health Bill is unnecessary, infringes civil liberties, is based on unsafe and bad science, and threatens breeds of special genetic importance with extinction.

 

 

A. Introduction

 

The Animal Health Bill has been introduced as a reaction to the FMD/2001 outbreak in UK, but it is directed at the control of any disease outbreak. It must be opposed because:-

 

7         it proposes to give unprecedented and unacceptable powers to government officials;

7         it is based on unsound science;

7         it undermines principles of civil liberties;

7         it does not provide proper and adequate compensation;

7         it does not provide an adequate right of appeal.

 

All these aspects are the subject of other submissions. This submission focuses specifically on the effect of the Bill with regard to scrapie.

 

This document has been prepared because of the special status and genetics regarding scrapie of native breeds of sheep, including particularly Northern Short-Tailed sheep. It refers to the likely effects of the Animal Health Bill, and arises naturally from discussions initiated by Dr June Morris and Lawrence Alderson with MAFF at a National Sheep Association meeting at Worcester on 17 October 2000. At that meeting it was stated that primitive sheep would be exempt from the initial stages of the National Scrapie Plan (NSP) (see Appendix 2).

 

In our opinion several questions should be resolved before any possibility of slaughtering sheep on the basis of scrapie-susceptible genotypes is considered.

 

1.       Scrapie has no known adverse effect on human health. No links between scrapie and CJD have been demonstrated. It has been present in the sheep population of UK for more than two hundred years, and no association with human disease has been shown. In Iceland, where sheep heads, eyes and brains are eaten, only two cases of CJD have been recorded in 35 years, and both were in a non-scrapie endemic region (Sigurdarson, 1991).

 

2.       The reason for slaughtering sheep with scrapie-susceptible genotypes, and the current policy of the National Scrapie Plan, both are based on the possible transfer of BSE to sheep. There is no evidence this has occurred. The Horn report, considered at the meeting of SEAC in September 2001, states that no scrapie strain with the characteristics of the BSE strain has been identified.

 

3.       It also needs to be borne in mind that it has not yet been proved that BSE is the cause of vCJD.

 

 

 

B. Animal Health Bill

 

7         Section 35(2): Transmissible spongiform encephalopathies (TSEs) have been added to the list of diseases detailed in the Animal Health Act 1981.

 

7         The Bill allows for the slaughter of any animals that the Minister thinks should be slaughtered.

 

7         Section 36A: The Bill allows the Minister to specify sheep genotypes which are more susceptible than other genotypes to scrapie.

 

7         Section 36C(2): The Minister may consider whether there are exceptional circumstances that allow susceptible sheep to be used for breeding.

 

7         Section 36D(1): The only appeal procedure allowed is to a person appointed by the Minister.

 

 

 

C. Impact of the application of the powers allowed by the Animal Health Bill

 

 

1. Loss of breeds and genetic material

 

a.       Section 36A: All genotypes, other than ARR/ARR are considered susceptible to scrapie or may act as carriers of scrapie. Thus all sheep with a genotype other than ARR/ARR are subject to the Minister's decision to slaughter.

 

b.       A significant number of native British breeds of sheep have a nil or very low frequency of ARR. In particular, breeds in the Northern Short-Tailed, Marsh and Mountain groups fall into this category (see Appendix 1). Some of these breeds are classified by Rare Breeds International as breeds of special genetic importance. In particular:

 

7         Herdwick sheep are specially adapted to a localised environment and are an integral part of the ecology of the Lake District.

7         British Milksheep achieve the highest performance and productivity of all native breeds.

7         Breeds in the Northern Short-Tailed group, such as the seaweed-eating North Ronaldsay, are distinctive and are an important part of the biological diversity of UK.

 

c. With the potential application of the powers contained in the Animal Health Bill these breeds

would cease to exist or would remain only as relic groups.

 

d. This is in direct contradiction of the Convention on Biological Diversity (UK was a signatory on 12

June 1992) which requires the maintenance of genetic diversity in domestic livestock.

 

e.       The extinction or severe reduction of any of these breeds of special genetic importance will cause an irretrievable loss of genetic material. The susceptible genotypes which will be eliminated are associated with other significant and valuable factors (see C3b below). The losses already experienced as a result of the policy of mass slaughter to control FMD/2001 are significant for some breeds listed in C1b, namely Herdwick 35% loss, British Milksheep 50% loss, Rough Fell 40% loss and Hill Radnor 30% loss. The losses from the implementation of policies contained in the Animal Health Bill could cause 100% loss in some breeds.

 

2. Exceptional circumstances

 

a.       Clause 36C(2): No details are provided regarding the possible qualifications for exceptional circumstances'. Correspondence between Lawrence Alderson (RBI) and DEFRA officers in the NSP unit during October and November 2001 has provided some clarification as follows in that exceptional circumstances might include:

 

7         "- - - rare breeds of sheep

 

7         - - - other sheep breeds of high value whose survival is necessary to preserve statutorily

protected landscapes.

 

7         - - - animals which would be valuable for research into scrapie/TSE."

 

 

b.       These points raise further important issues for debate:

 

7         Claims or proposals for exceptional circumstances' can be made only if the definition of that qualification is detailed clearly.

 

7         The list of sheep breeds defined as rare breeds which DEFRA currently holds does not coincide with the standard list provided by Rare Breeds International (see Appendix 3). It excludes several breeds of special genetic importance.

 

7         If susceptible animals are permitted to survive what will be their function? Will they be permitted to enter the food chain, or will they be museum pieces?

 

 

3. Genetic and scientific implications

 

The dangers of the powers for slaughter as permitted by the Animal Health Bill, and of selection for ARR homozygosity as required by the National Scrapie Plan, have not been properly evaluated. There is not a proper understanding of the function and inter-relationship of alleles associated with scrapie. The Animal Health Bill and the National Scrapie Plan are based on bad and unsafe science. The following items should be considered in the application of the proposed controls with regard to scrapie:

 

a.       Loss of distinctive and valuable breeds (see C1b above).

 

b.       Loss of alleles of current or potential value. The prion protein is considered to have a role in many important functions, including:

7         copper homeostasis

7         neuronal and nerve function

7         free radicals and disease

7         Signal transduction (Martins et al, 2001). Prion protein has been shown to trigger the activation of tyrosine kinase. Tyrosine kinase has been linked with a genetic defect, hereditary chondroplasia, of Suffolk and some other black-faced sheep. The latter defect involves an amino acid substitution in the tyrosine kinase domain of fibroblast growth factor receptor 3.

 

c.       Other characteristics which may be affected by selection include:

7         wool colour: in coloured breeds, the frequency of the ARR genotype is higher in animals with white wool. A gene for prion protein production and the agouti gene for colour are both located on chromosome 13. Coloured sheep are typical of ancient breeds.

7         overall merit: negative correlation between ARR and animals of superior commercial merit. In several breeds the superiority of non-ARR genotypes has been noted.

 

d.       Unresolved questions relating to prion protein and scrapie. The inter-relationship of different prion protein genotypes and various strains of scrapie is not properly understood. In particular, there is some evidence that animals with a scrapie-susceptible genotype may be resistant to BSE infection.
 
Until further research has been carried out, any selection for particular genotypes or slaughter of sheep of a particular type, is dangerous. The Bill, in our current state of knowledge, is based on unsafe science. For example, ARQ genotype appears to be at risk from group C scrapie strains, while VRQ genotype appears to be at risk for group A scrapie strains. However, H (histidine) at codon 154 appears to confer resistance in some breeds (e.g. Icelandic), and this may be found to relate to functions involving copper as histidine binds copper and zinc.
 
Many questions have not been fully resolved:

7         Does the strain of scrapie prion affect resistance/susceptibility of a particular genotype?

7         Can the metal ion content of the environment modify the strain? Metal binding, particularly of copper and zinc, has been shown to interconvert strains of prion protein associated with CJD (Wadsworth et al, 1999).

7         Will mutations arise, followed by selection, which will affect the resistance of the ARR genotype?

7         Is the ARR animal completely free of the scrapie prion protein, or is the incubation period sufficiently long for absence of clinical signs (i.e. can these animals act as carriers)?

7         The extent and significance of scrapie strain variation is not clear (Horn report to SEAC meeting September 2001).

 

 

 

D. Conclusions

 

7         The Northern Short-Tailed, Marsh and Mountain are distinctive groups of sheep which deserve special consideration in the application of policy and programmes for the control of scrapie.

 

7         The current policy of DEFRA allows variation from the NSP for some numerically scarce (rare) breeds in the short-term. There may also be exemptions for some breeds under exceptional circumstances' from slaughter under the amended Animal Health Act. However, several breeds which are classified as breeds of special genetic importance by RBI, and which possess a low frequency of the scrapie-resistant allele, are not included on the DEFRA list. This must be remedied.

 

7         We seek to establish with DEFRA clear guidelines and guarantees for all breeds that are threatened by the implementation of the Animal Health Bill if it is not amended

 

7         It is important to conserve not only the genome of individual breeds, but also the genetic variability (alleles) within those breeds.

 

7         Susceptible breeds of great genetic importance (see Appendix 1) must be protected from the danger of extinction and from the dangers of inbreeding which may result from reduction of their breeding population through culling of non-ARR animals. Their genetic integrity must be protected by the avoidance of crossing with other breeds to increase the frequency of ARR.

 

7         It is important to mount further studies to investigate the effect of the loss of genetic material, and to resolve unanswered questions (see C3b and C3c above), before mandatory selection for the ARR genotype is imposed on susceptible breeds.

 

7         Breeders of susceptible breeds require the security of longer-term guarantees of strategies to support breeds with low ARR frequency in order to conserve their distinctive genome.

 

 

 

 

Further information available from:

 

Lawrence Alderson E-mail: alderson@clltd.demon.co.uk Tel: 01952 510154

 

Peter Titley E-mail: peter@outlane.fsbusiness.co.uk Tel: 01785 850183

 

Dr June Morris E-mail: june@meveril.fsnet.co.uk

 

 

 

 

 

 

 

 

 

 

 

 


Appendix 1

 

 

Scrapie Genotypes

 

British breeds fall into distinct groups wherein longwool breeds have a high level of ARR homozygosity, and short-tailed breeds have a high level of ARQ homozygosity. Other groups are intermediate.

 

 

Longwool high ARR homozygosity 85-100%

Grassland/heath 40-80%

Down 30-70%

Mountain 20-50%

Marsh' nil-20%

Northern Short-Tailed low or nil ARR frequency nil-20%

 

 

Breeds from the three groups with the lowest ARR frequency are found in UK, namely Northern Short-Tailed, Marsh' and Mountain breeds.

 

Native Northern Short-Tailed breeds in UK are Soay, Castlemilk Moorit, Boreray, North Ronaldsay, Shetland, Manx Loghtan and Hebridean. Non-native NST breeds in UK are Icelandic, Ouessant, Finn, Gotland, Romanov, Mouflon (all European) and Barbados Blackbelly. 'Marsh' breeds in UK are British Milksheep (native) and East Friesland and Zwartbles (European). Native mountain breeds with a low frequency of ARR include the Herdwick where only 5.1% of animals are ARR/ARR (Hunter et al, 1997).

 

All the native breeds listed above are included on the Rare Breeds International list of breeds of special genetic importance, and the frequency of the ARR genotype (*Hunter et al, 1997; **Thorgeirsdottir et al, 1999) is shown below.

 

 

ARR frequency in Northern Short-Tailed and Marsh breeds in UK

 

ARR frequency No. tested

NST: *Soay 5.8% 26 RBI listed in UK

Castlemilk Moorit 1.4% 35 RBI listed in UK

Boreray RBI listed in UK

North Ronaldsay nil 14 RBI listed in UK

*Shetland RBI listed in UK

Manx Loghtan RBI listed in UK

Hebridean RBI listed in UK

**Icelandic nil 932

Ouessant

Finn

Gotland

Marsh: British Milksheep nil few RBI listed in UK

East Friesland 3.0% 93

Zwartbles 16.5% 115

 

 

 

 

 

 

 


Appendix 2

 

Notes on the National Scrapie Plan

NSP imposes immediate restrictions on the use of rams with ARQ/ARQ and VRQ (except ARR/VRQ) genotypes. Other genotypes will be unaffected until the end of 2004. Thereafter, increasing restrictions will be applied, and from 2007 the policy has not been declared but is likely to be focused on selection for the ARR/ARR genotype. This policy is damaging to breeds with a low frequency of the ARR allele.

 

 

NSP Policy related to Genotype

 

ARR/ARR Most resistant; no restriction on use of rams with this genotype.

 

ARR/ARQ Genetically resistant to scrapie but careful selection is advised when used for breeding.

ARR/ARH

ARR/AHQ

AHQ/AHQ Little resistance to scrapie, but may be sold or used for breeding without restriction until the end

ARH/ARH of 2004. Thereafter, any ram on a scheme farm may continue to be used for breeding for a

ARQ/ARH further three years (except ARQ/ARQ - which will be subject to scientific review after the first

AHQ/ARH year) or until the end of its life, whichever is sooner.

ARQ/AHQ

ARQ/ARQ

ARR/VRQ Genetically susceptible to scrapie but may exceptionally be used for further (controlled) breeding

in the context of an approved breeding programme

 

ARQ/VRQ Highly susceptible and must be humanely slaughtered or castrated.

ARH/VRQ

AHQ/VRQ

VRQ/VRQ

 

 

 

 

 

 

 

Appendix 3

 

Native British sheep recognised by Rare Breeds International as breeds of special genetic importance as at 1 January 2001 (Note: breed priorities may change following losses during the FMD outbreak):

 

Category 1 Boreray, North Ronaldsay, Soay

 

Category 2 Castlemilk Moorit, Hebridean, Leicester Longwool, Manx Loghtan, Teeswater, Whitefaced Woodland

 

Category 3 Balwen, British Milksheep, Cotswold, Dorset Horn, Herdwick, Norfolk Horn, Portland, Wensleydale, Wiltshire Horn

 

Category 4 Badger Face Welsh Mountain, Dartmoor, Devon & Cornwall Longwool, Dorset Down, Hill Radnor, Kerry Hill, Lincoln Longwool, Llanwenog, Oxford Down, Rough Fell, Shetland, Shropshire, Southdown

References

 

Hunter N, Goldmann W, Foster J D, Cairns D, Smith G. 1997. Natural scrapie and PrP genotype: case-control studies in British sheep. Veterinary Record, 141, 137-140

 

Martins V R, Mercadante A F, Cabral A L B, Freitas A R O, Castro R M R P S. 2001. Insight into the physiological function of cellular prion protein. Brazilian J. Med. & Biol. Res. 34, 585-595

 

Sigardsun S. 1991. Epidemiology of scrapie in Iceland and experience with control measures. In: Sub-acute Spongiform Encephalopathies. Bradley R et al (eds)

 

Thorsgeirsdottir S, Sigurdarson S, Thorisson H M, Georgsson G, Palsdottir A. 1999. PrP gene polymorphism and natural scrapie in Icelandic sheep. Journal of General Virology, 80, 2527-2534

 

Wadsworth J D F, Hill A F, Joiner S, Jackson G S, Clarke A R, Collinge J. 1999. Strain-specific prion-protein conformation determined by metal ions. Nature Cell Biology 1, 55-59

 

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