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Agriculture: Scrapie

Answer

No reliable estimate is available of the distribution of the 15 known scrapie genotypes of sheep in the national ram flock prior to the commencement of the first National Scrapie Plan (NSP) genotype testing in 2001. Relatively few breeds had been commercially testing their rams prior to 2001. Modelling done prior to the NSP(1) estimated that approximately 28 per cent of rams were of the most resistant genotype that carries two copies of the ARR allele(2) (the allele that is most resistant to classical scrapie) and that thus had the ““ARR/ARR”” or NSP Type 1 genotype. There are 420,000 rams and ram lambs in the national flock. Since 2001, the NSP has tested over 2.6 million sheep (in all schemes) in Great Britain. Table 1 below shows the genotypes of all of those sheep. Table 2 illustrates the change in the allele percentage of ram lambs born in flocks participating in the NSP from 2002 to 2005 (the ARR allele is the most resistant to classical scrapie and the VRQ is the most susceptible in the majority of breeds). The ram lamb data for 2002 are a good starting point as the majority of these animals will have been the progeny of previously untested rams as NSP testing only commenced on a small scale in October 2001. (1) Arnold et al. Published in Preventative Veterinary Medicine 56, 227-229 (2002). (2) Gene component derived from one parent and contributing hereditary information from that parent.

Table 1NSP data as at 29/12/2006	2001-06All sheep tested in all NSP schemes
NSP Type	Genotype & Degree of resistance/susceptibility to classical scrapie	Number	Per cent
I	ARR/ARR	Sheep that are genetically most resistant to scrapie.	849,304	32.3%
II	ARR/AHQ	Sheep that are genetically resistant to scrapie, but will need careful selection when used for further breeding.	251,464	9.6%
ARR/ARH	143,612	5.5%
ARR/ARQ	714,617	27.1%
III	AHQ/AHQ	Sheep that genetically have little resistance to scrapie and will need careful selection when used for further breeding.	40,552	1.5%
AHQ/ARH	10,061	0.4%
AHQ/ARQ	139,571	5.3%
ARH/ARH	35,488	1.3%
ARH/ARQ	35,961	1.4%
ARQ/ARQ	237,291	9.0%
IV	ARR/VRQ	Sheep that are genetically susceptible to scrapie and should not be used for breeding unless in the context of a controlled breeding programme approved by the NSP Administration Centre.	90,708	3.4%
V	AHQ/VRQ	Sheep that are highly susceptible to scrapie and should not be used for breeding.	20,236	0.8%
ARH/VRQ	6,039	0.2%
ARQ/VRQ	48,755	1.9%
VRQ/VRQ	4,489	0.2%
Unknown	-		4,940	0.2%
Total tested	2,633,088	100.0%

Table 2Changes in allele per cent frequencies of ram lambs 2002-05
	ARR	AHQ	ARH	ARQ	VRQ
2002	50.4	7.4	9.9	29.2	3.0
2003	55.6	7.5	7.7	26.9	2.3
2004	62.0	6.5	6.9	22.9	1.7
2005	65.4	5.9	6.3	20.9	1.5

Secondary information

Type

Written question

Reference

1040; 688 c116-7WA

Session

2006-07

Subjects

Genetics Disease control Testing Sheep Scrapie

Contains statistics

Yes

Link

View this Written question on www.publications.parliament.uk