Testing the equivalence of different ovine PrP genotypes for estimated breeding values

In this study we applied equivalence testing methods to prove the absence of differences in genetic values of ewes with different PrP genotypes. In particular, the milk production genetic value equivalence of ARR ovine prion protein (PrP) genotypes was analysed. There is no scientific evidence implying that the performances and genetic values of different PrP genotypes will be different, but it is interesting to confirm that the performance of one genotype is indistinguishable from another before starting a genetic scrapie control programme. Genotyping was performed on 204 ewes from a Spanish population of Lacaune breed. Ewes were sampled from the lower and upper tails for the distribution of estimated breeding value (EBV) for standardized lactation. The conditional probability that the number of ARR alleles contained in the group of higher EBV was larger than that found in the group of lower EBV was found to be in the interval between the true value (1/2) and two different pre-specified bounds (0.1 and 0.2). The results evidence the equivalence of ARR PrP genotypes for milk production EBV, and lead to the conclusion that the average genetic values for milk production of Lacaune flocks considered will not be affected by the selection of ewe carriers of resistance scrapie alleles (p<0.05).