IDENTIFICATION OF LOCI WITH SIGNIFICANT EFFECTS ON STILLBIRTH AND CALVING DIFFICULTIES IN HOLSTEIN CATTLE

Marker assisted selection (MAS) uses genetic marker genotypes to predi ct an animal's performance potential and will provide additional infor mation for progeny testing. To implement MAS, quantitative trait loci (QTL) must be identified and then manipulated with the aid of linked m arkers. The aim of this study was the identification of QTL underlying the genetic variation of the traits stillbirth and calving difficulti es in dairy cattle. Twelve paternal half-sib families comprising a tot al of 498 sons were used in a granddaughter design. Altogether, nine a utosomal microsatellites which mapped to chromosomes 1, 6, 9, 13, 14, 16, 19, and 23 were genotyped. Bulls' estimated breeding values for st illbirth and calving difficulties (paternal and maternal components) w ere used as trait data. Statistical analyses of association between ma rker genotypes and trait data were conducted in the frame of a grandda ughter design model. Paternal components of stillbirth and calving dif ficulties were significant (P less than or equal to 0.05) in 4 of the 8 families analyzed for CYP21 (23q21). The marker ETH8 localized on ch romosome 6 (6q35) also had a significant effect (p less than or equal to 0.05) on calving difficulties. These significant effects suggested the presence of a QTL responsible for both the paternal component of c alving difficulties and the paternal component of stillbirth on chromo some 23, in linkage to the marker CYP21.