Association analyses between the Prion Protein locus and reproductive and lamb weight traits in Ripollesa sheep

¹ Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
² Associació Nacional de Criadors d'Ovins de Raça Ripollesa, 17121 Monells, Girona, Spain
³ Servei Veterinari de Genètica Molecular, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

^* To whom correspondence should be addressed. E-mail: gerardo.caja{at}uab.es.

	Abstract

The objective of this study was to analyze the association between the haplotypes of the prion protein (PrP) locus and several reproductive and lamb weight traits in Ripollesa sheep. Prion protein genotypes were available for a total of 310 sheep (7 rams, 114 ewes, and 189 lambs), all of them belonging to the purebred Ripollesa flock of the Universitat Autònoma of Barcelona in which all sheep had a known pedigree. In addition, the genotype of 24 historical descendants of the previously genotyped adult individuals was reconstructed, provided that both parents were homozygous for PrP haplotypes. Only three haplotypes (ARR, ARQ, and ARH) were observed in the PrP locus of the sampled sheep. Reproductive traits included conception rate and litter size, whereas birth BW and 90 d BW were the lamb weight traits studied. The additive effect of PrP haplotypes was analyzed through Bayesian animal threshold and linear models, for reproductive and weight traits, respectively. Ewe reproductive data belonged to 89 ewes that gave 492 conception rate records and 440 litter size records. Analyses of BW at birth and at 90 d of age were made on 323 and 164 lamb records respectively. No associations between PrP haplotypes and conception rate and BW traits were observed. For litter size, the effect of the ARH haplotype was greater than that of the ARQ haplotype. Differences between ARH and ARR haplotypes also suggested an advantage for the ARH one. As a whole, our results indicated that the selection favorable to increase litter size in Ripollesa ewes may also increase the ARH haplotype frequency, which contradicts the recommendations of the current European Union legislation aiming to increase the genetic resistance to scrapie. As a consequence scrapie genotyping needs to be included as a new selection criterion in the breed.

Key Words: prion protein, birth weight, litter size, conception rate, Ripollesa breed, sheep

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