Refined mapping of a QTL for somatic cell score on BTA27 in the German Holstein using combined linkage and linkage disequilibrium analysis

Abstract

Genetic selection for udder health is often based on the indicator trait somatic cell score (SCS), which is correlated with clinical mastitis and has a moderate heritability. We used combined linkage and linkage disequilibrium analysis to refine mapping of a previously reported quantitative trait locus (QTL) affecting SCS on Bos taurus autosome 27 (BTA27) in the German Holstein population. A granddaughter design of six grandsire families with 492 sons progeny tested for an average of 190 daughters per son was investigated. Nineteen microsatellite markers were genotyped along a segment of 26.2 cM proximally on BTA27. A chromosome-wide significant QTL was identified between DIK2879 and KIBS272 using combined analysis. The region of interest for future fine mapping experiments was narrowed to the marker interval KIBS272-DIK2191 with a confidence interval of 3.27 cM. The QTL was estimated to be responsible for 18% of the genetic variation in SCS. Application of a 2-QTL model did not result in higher test statistics. Animals likely to be heterozygous or homozygous at the QTL were identified. This study provides a basis for the selection of further markers in linkage disequilibrium with the QTL affecting SCS on BTA27. Key words: Fine-mapping, mastitis, BTA27, somatic cell score, Holstein