[Jacob-list] Fwd: [OrganicShepherding] Primitive Sheep breeds

[linda]

Found this on another list - thought it was interesting.
Linda

> The Case for Exempting Primitive Sheep from the National Scrapie Plan
>
> by
>
> June Morris
>
>
>
> Will scrapie genotype selection lead to loss of our pure ancient breeds of
> sheep?
>
> A consultation document for a National Scrapie Plan for Great Britain has
> been issued by the Ministry of Agriculture, Fisheries and Food. Replies are
> required by October 31st 2000. Below are some arguments against
> implementation of scrapie genotyping for sheep breeds belonging to the
> Northern Short-tail group.
>
> Three main concerns are:
>
> 1. These are unique ancient breeds where selection for a particular
> expression of any character would risk the loss of a unique genetic
> resource.
>
> 2. These are breeds where there appears to be a complete lack of the
> 'resistant Codon 136 154 171 genotype' AA RR RR, or it may occur
> infrequently in the population.
>
> 3. There is to date incomplete information about the role of the prion
> protein. There is, however, sufficient indication that it may have an
> important role in, for example, resistance to oxidative stress and possibly
> copper homeostasis. It may be significant when considering the Northern
> short-tail group of sheep that the gene coding for the prion protein is
> found on chromosome 13, the same chromosome on which the Agouti gene,
> affecting the colour of the sheep is located. The Northern short-tails are
> coloured sheep breeds.
>
> Each of these points is addressed in more detail below.
>
> 1. Unique ancient breeds
>
> In Britain we are fortunate to have the remnants of two ancient breeds of
> sheep.
>
> i. The SOAY on islands in the St Kilda archipelago off the west coast of
> Scotland.
>
> ii. The NORTH RONALDSDAY on the most northerly island of that name in
> Orkney.
>
> I am not aware of any scrapie in either of these indigenous island sheep
> populations. Each of these breeds is kept in smaller numbers in flocks on
> mainland Britain. Archaeological settlements from 5000 years ago had
> skeletons of this type of sheep. Other ancient members of the Northern
> short-tail group of sheep include the Icelandic, Norwegian and the French
> Ouessant sheep. Icelandic and Ouessant sheep are also kept in Britain.
>
> These ancient breeds remain because of minimal selection by man and it is
> generally agreed that selection for a particular expression, morphological,
> physiological or biochemical, would be inappropriate. Furthermore, there are
> many examples where selection for one character often has an unexpected
> effect on other, apparently unrelated, characters.
>
> 2. Lack of scrapie-resistant genotype in these breeds.
>
> Codon 136 154 171 Codon 136 154 171
>
> AA RR QQ rather than the 'desirable' AA RR RR, appears to be the prion
> protein genotype characteristic of many Northern short-tail breeds. Thus
> Thorgeirsdottir et al 1999 found that in 932 Icelandic sheep no polymorphism
> occurred at Codon 171, only the glutamine allele (Q) was found.
>
> These authors mention that the prion protein ARQ background seems to be the
> ancestral genotype in sheep. Where we are fortunate enough to have ancient
> breeds, it is therefore very important to maintain this ancestral genotype.
>
> A similar situation is seen in the Soay sheep. Hunter et al 1997 found that
> 92% of the 26 sheep genotyped were homozygous for ARQ. One animal was
> heterozygous for ARQ and only 1 Soay sheep had the AA RR RR 'resistant
> genotype'.
>
> Although not published, North Ronaldsay sheep also appear to be
> characteristically AA RR QQ.
>
> One could perhaps argue that if the homozygous ARQ is the ancestral sheep
> genotype, and therefore characteristic of the remaining ancient sheep
> breeds, that any deviation from this may represent inadvertent crossing with
> other breeds.
>
> 3. Normal role of the prion protein.
>
> The link made by Brown et al 1997 between normal prion protein and
> resistance to oxidative stress has many implications for the ability of an
> animal to withstand disease. Free radical production is implicated with
> disease, stress conditions, some plant toxins, and pesticides. The ability
> of an animal to deal with these free radicals, using enzymes such as
> superoxide dismutase and glutathione peroxidase, is very important. Brown et
> al 1997, in studies on isolated cells, have linked levels of both these
> antioxidant enzymes to normal prion protein content. Brown et al also
> suggest that prion protein expression is associated with regulation of
> resistance to oxidative stress in skeletal muscle. This raises the question
> as to whether, by selecting for particular prion protein genotypes, we may
> be inadvertently altering the animal's ability to cope with disease, stress,
> even some toxic plants and the wide range of agrochemicals used.
>
> Prion protein and copper.
>
> It is of particular interest when considering North Ronaldsay sheep that a
> number of publications have linked copper with prion protein. The prion
> protein has in fact been found to bind copper. North Ronaldsay sheep are the
> most copper sensitive sheep. Their ability to accumulate copper has been
> related to their unique diet of almost completely seaweed on their native
> island. Seaweed contains a number of substances, which reduced the
> bioavailability of copper. Wadsworth et al 1999 demonstrated that copper
> could affect the prion protein conformation and two human types of the prion
> protein found in subtypes of Creutzfeldt-Jacob disease could be
> interconverted by binding of copper or zinc. The authors even raise the
> possibility that drugs which have an effect on copper metabolism may be of
> therapeutic value in prion disease. Waggoner et al 1999 suggest a role for
> the prion protein in regulating copper homeostasis at the membrane level.
>
> To summarise: we have important ancient coloured breeds of sheep in Britain
> with the ancestral prion genotype at codons 136, 154, 171 of AA RR QQ. Pure
> bred animals with the 'scrapie resistant' genotype AA RR RR may not exist,
> and in terms of the continued existence of these ancient breeds it would be
> inappropriate to attempt any selection on this basis. These ancient breeds,
> unlike many highly selected modern sheep breeds, have the ability to survive
> outdoor conditions with minimal care by man. They are also 'gene banks' with
> a genetic diversity exceeding modern breeds. Indeed the suggestion of a role
> for prion protein in dealing with oxidative stress may be an integral part
> of their survival. I ask, therefore, that these ancient breeds of sheep,
> belonging to the Northern short-tail group, should be considered separately
> and should not, like many breeds in the past, become an irreversible
> casualty of man's selection.
>
>
>
> June Morris Ph.D. (September 2000)
>
>
>
> References
>
> Brown, D.R., Schmidt, B., Groschup M. H., Kretzschmar, H.A. 1998. Prion -
> protein expression in muscle cells and toxicity of a prion protein fragment.
> European Journal of Cell Biology, 75, 29-37.
>
> Brown D. R., Schmidt, B., Kretzschmar H.A. 1997, Effects of oxidative stress
> on prion protein expression in PC12 cells, International Journal of
> Developmental Neuroscience. 15,8, 961-972.
>
> 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
>
> Thorgeirsdottir, 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
>
> Waggoner D.J., Bartnikas T.B., Gitlin D, 1999. The Role of Copper in
> Neurodegenerative Disease. Neurobiology of Disease 6, 221-230.
>

www.PatchworkFibers.com
Registered Jacob Sheep