Associations between lamb survival and prion protein genotype: analysis of data for ten sheep breeds in Great Britain

Survival times from birth to weaning were analysed for over 38000 lambs (2427 dead and 36096 live lambs) from 128 flocks using Cox proportional hazard models for each breed, including additive animal genetic effects. No significant associations between PrP genotype and lamb survival were identified, except in the Charollais breed for which there was a higher risk of mortality in lambs of the ARR/VRQ genotype compared with those of the ARR/ARR genotype. Significant effects of birth weight, litter size, sex, age of dam and year of birth on survival were also identified. For all breeds the reasons for death changed significantly with age; however, no significant associations between reason for death and PrP genotype were found for any of the breeds.This study found no evidence to suggest that a selective breeding programme based on PrP genotype will have a detrimental effect on lamb survival. The only significant effect of PrP genotype identified was likely to be of little consequence because an increased risk of mortality was associated with a genotype that is selected against in current breeding strategies.Large-scale selective breeding programmes have been introduced throughout the European Union to reduce the risk of sheep transmissible spongiform encephalopathies (TSEs) and, in particular, the risk to human health posed by the possible presence of bovine spongiform encephalopathy (BSE) in sheep [1]. These programmes exploit a strong host genetic component at the ovine prion protein (PrP) gene, which influences both the risk of infection and the incubation period for scrapie [2-4]. They aim to decrease the frequency of high risk alleles (ARQ and VRQ) and increase the frequency of the major low risk allele (ARR).Concerns have been expressed, however, that such large-scale breeding programmes based on one specific factor (in this case, PrP genotype) could have detrimental side-effects on sheep performance. These concerns stem from farmers' assertions that sheep carry