title: Identification of a two-marker-haplotype on Bos taurus autosome 18 associated with somatic cell score in German Holstein cattle.
abstract: BACKGROUND
  The somatic cell score (SCS) is implemented in routine sire evaluations in many countries as an indicator trait for udder health. Somatic cell score is highly correlated with clinical mastitis, and in the German Holstein population quantitative trait loci (QTL) for SCS have been repeatedly mapped on Bos taurus autosome 18 (BTA18). In the present study, we report a refined analysis of previously detected QTL regions on BTA18 with the aim of identifying marker and marker haplotypes in linkage disequilibrium with SCS. A combined linkage and linkage disequilibrium approach was implemented, and association analyses of marker genotypes and maternally inherited two-marker-haplotypes were conducted to identify marker and haplotypes in linkage disequilibrium with a locus affecting SCS in the German Holstein population.
  
  
  RESULTS
  We detected a genome-wide significant QTL within marker interval 9 (HAMP_c.366+109G>A--BMS833) in the middle to telomeric region on BTA18 and a second putative QTL in marker interval 12-13 (BB710-PVRL2_c.392G>A). Association analyses with genotypes of markers flanking the most likely QTL positions revealed the microsatellite marker BMS833 (interval 9) to be associated with a locus affecting SCS within the families investigated. A further analysis of maternally inherited two-marker haplotypes and effects of maternally inherited two-marker-interval gametes indicated haplotype 249-G in marker interval 12-13 (BB710-PVRL2_c.392G>A) to be associated with SCS in the German Holstein population.
  
  
  CONCLUSIONS
  Our results confirmed previous QTL mapping results for SCS and support the hypothesis that more than one locus presumably affects udder health in the middle to telomeric region of BTA18. However, a subsequent investigation of the reported QTL regions is necessary to verify the two-QTL hypothesis and confirm the association of two-marker-haplotype 249-G in marker interval 12-13 (BB710-PVRL2_c.392G>A) with SCS. For this purpose, higher marker density and multiple-trait and multiple-QTL models are required to narrow down the position of the causal mutation or mutations affecting SCS in German Holstein cattle.
authors.affiliation: Research Unit Molecular Biology, Research Institute for the Biology of Farm Animals, 18196 Dummerstorf, Germany. brand@fbn-dummerstorf.de
authors.forename: Bodo
authors.initials: B
authors.lastname: Brand
authors.forename: Christine
authors.initials: C
authors.lastname: Baes
authors.forename: Manfred
authors.initials: M
authors.lastname: Mayer
authors.forename: Norbert
authors.initials: N
authors.lastname: Reinsch
authors.forename: Christa
authors.initials: C
authors.lastname: Kühn
mesh_terms: D000818:Animals; D002417:Cattle / Q000235:genetics*; D002874:Chromosome Mapping / Q000662:veterinary; D033481:Chromosomes, Mammalian; D055028:Comparative Genomic Hybridization; D005819:Genetic Markers; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D015810:Linkage Disequilibrium; D018895:Microsatellite Repeats; D010641:Phenotype; D040641:Quantitative Trait Loci; D016615:Telomere / Q000235:genetics
chemical_list: D005819:Genetic Markers