THE occurrence of natural scrapie in sheep is influenced by polymorphisms in the ovine prion protein (PrP) gene. The PrP gene is located on chromosome 13 in cattle and sheep (Castiglioni et al 1998), and on chromosome 20 in humans (Sparkes et al 1986). The ovine PrP gene has three exons which are 52, 98 and 4028 nucleotides in length, separated by two introns, 2421 and 14031 nucleotides in length (Lee et al 1998). In exon 3 of the gene, the alanine (A) to valine (V) polymorphism at codon 136 and the glutamine (Q) to arginine (R) polymorphism at codon 171 contribute to sus- ceptibility to developing clinical signs of scrapie (Laplanche et al 1993, Belt et al 1995, Clouscard et al 1995, Hunter et al 1996, 1997a, Junghans et al 1998, Elsen et al 1999, Thorgeirsdottir et al 1999, Tranulis et al 1999). The associa- tion between scrapie susceptibility and polymorphisms at codon 154 are currently unclear, but there is a possibility that histidine at codon 154 may offer protection from scrapie in some breeds of sheep (Elsen et al 1999, Thorgeirsdottir et al 1999). Polymorphisms at codons 112, 137, 138, 141, 151 and 211 are rare and have not been associated with any dis- ease phenotype in natural and experimental scrapie (Laplanche et al 1993, Bossers et al 1996, Thorgeirsdottir et al 1999, Tranulis et al 1999). The polymorphisms at codon 171 are seen in all breeds, with the exception of the Icelandic breed, where in a total of 932 sheep studied, all carried the QQ 171 variant (Thorgeirsdottir et al 1999). In sev- eral breeds such as Cheviot, Texel, Ile de France and Romanov (Laplanche et al 1993, Belt et al 1995, Hunter et al 1996), scrapie susceptibility is increased by the presence of at least one V 136 allele. Currently there are an estimated 8 . 5 million sheep in Ireland (Central Statistics Office 1999). The principal enter- prise of lowland sheep farmers is production of mid-season lamb sired by terminal sire breeds (Suffolk, Texel, Charollais, Bleu du Maine, Rouge de l’Ouest, Vendéen). The Bleu du Maine, Rouge de l’Ouest, Charollais and Vendéen are terminal sires of French origin, while the Texel originated on the Isle of Texel in the Netherlands. Some rarer breeds also exist in Ireland. The Galway is an Irish native lowland breed whose numbers have decreased ra- pidly in the last 20 years and it is now classed as a rare breed. Upland and mountain sheep farming is based on flocks of Blackface Mountain and Wicklow Cheviot ewes. About 2 million sheep in Ireland are maintained on hills and mountains. The Mayo Blackface Mountain breed was origi- nally imported from Scotland in 1902 but is genetically dis- tinct from other Blackface Mountain sheep in different parts of Ireland which were imported at different times. Donegal Blackface Mountain sheep have been bred with imported strains of Scottish Blackface. The Wicklow Cheviot breed is noted for hardiness, freedom from foot rot and prolificacy, with good wool producing abilities. The development of the Belclare breed was initiated in 1978 at the Belclare Research Institute in Galway. Rams were released to the industry for crossing in 1985 comprising commercial flocks of purebred ewes drawn from the research flock at Belclare (Hanranan 1989). The aim of this study was to investigate the PrP genotype distribution in stock rams of five imported pedigree sheep breeds in Ireland, namely Texel, Rouge de l’Ouest, Bleu du Maine, Vendéen, Charollais, and five native pedigree breeds: Belclare, Galway, Wicklow Cheviot, Donegal Blackface Mountain and Mayo Blackface Mountain. Prion protein gene polymorphisms in pedigree sheep in Ireland E. O’DOHERTY, M. AHERNE, S. ENNIS, * E. WEAVERS, † J. F. ROCHE, ‡ T. SWEENEY § Department of Animal Husbandry and Production, Faculty of Veterinary Medicine, U.C.D., Ballsbridge, Dublin 4, † Central Veterinary Laboratory, Abbotstown, Castleknock, Dublin 15, Ireland SUMMARY The development of clinical signs of scrapie in sheep has been linked to polymorphisms in the prion protein (PrP) gene. The most important polymorphisms appear to be at codons 136, 154 and 171. The objective of this study was to investigate polymorphisms at these codons in five native (Belclare, Galway, Wicklow Cheviot, Donegal Blackface Mountain and Mayo Blackface Mountain) and five imported (Texel, Bleu du Maine, Rouge de l’Ouest, Vendéen and Charollais) sheep breeds in Ireland. A total of 13 geno- types were found. The percentage of the most resistant genotype AA 136 RR 154 RR 171 varied from 1 . 8 per cent in the Vendéen breed, 3 . 1 per cent in Donegal Blackface Mountain, 10 . 0 per cent in Texel, 11 . 1 per cent in Wicklow Cheviot, 12 . 9 per cent in Belclare, 22 . 0 per cent in Charollais, 25 . 6 per cent in Mayo Blackface Mountain, 33 . 3 per cent in Galway, 46 . 4 per cent in Bleu du Maine to 62 . 5 per cent in Rouge de l’Ouest. The results indicate that a significant amount of variation exists between the breeds analysed in this study. © 2001 Harcourt Publishers Ltd. 0034-5288/01/010051 + 06 $35.00/0 © 2001 Harcourt Publishers Ltd § Corresponding author: Department of Animal Husbandry and Production, Faculty of Veterinary Medicine, U.C.D., Ballsbridge, Dublin 4, Ireland. Fax 00 353 16600883; E-mail tsweeney@pop3.ucd.ie Current addresses: * National Centre for Medical Genetics, Our Lady’s Hospital for Sick Children, Crumlin, Dublin 12; ‡ Teagasc Headquarters, 19 Sandymount Avenue, Dublin 4, Ireland. Research in Veterinary Science 2001, 70, 51–56 doi:10.1053/rvsc 2000.0441, available online at http://www.idealibrary.com on