Pleiotropic effects of a QTL region for androstenone level on pig chromosome 6

A.M. Hidalgo^1,2, J.W.M. Bastiaansen², B. Harlizius³, E. Knol³, M.A.M. Groenen^2
1Swedish University of Agricultural Sciences, Department of Animal Breeding and Genetics, P.O. Box 7023, 750 07 - Uppsala, Sweden, ²Wageningen University, Animal Breeding and Genomics Centre, P.O. Box 338, 6700 AH - Wageningen, Netherlands, ³TOPIGS Research Center IPG, P.O. Box 43, 6640 AA - Beuningen, Netherlands; andre.hidalgo@wur.nl

Androstenone is one of the main compounds causing boar taint in boars. A 1.94 Mbp region on pig chromosome 6 (SSC6) was found to affect androstenone level. Within this region, two major haplotypes (high- and low-androstenone) can be distinguished. Analysis of sequence data showed that the low-androstenone haplotype originated from Asian breeds and was found at different frequencies in European commercial breeds. Because androstenone levels were not taken into account in typical breeding programs, we hypothesize that this haplotype accumulated indirectly by selection for another correlated trait. In this study, three pig lines were used for the estimation of pleiotropic effect of the 1.94 Mbp region on SSC6: sow line 1 (~1450 animals); sow line 2 (~1300 animals); and a boar line (~900 animals). Phenotypes were available for eight traits: birth weight, backfat thickness, growth rate, total number born, litter birth weight, teat number, sperm motility, and number of spermatozoa per ejaculation. Association between phenotypes and haplotypes were tested using ASReml v3.0. For both sow lines, a favorable effect for teat number (+0.11) was detected of the low-androstenone haplotype (p=0.058; p=0.013 respectively). In sow line 2, a favorable effect of the low-androstenone haplotype on number of spermatozoa per ejaculation was detected (p=0.023). No effects were identified on production and female reproduction traits. These results show that pleiotropic effects for androstenone level on SSC6 are favorable and have low magnitude. The absence of unfavorable pleiotropic effects suggests that selection for low-androstenone levels at this location is possible without negative effects on other traits.