Abstract
BackgroundThe 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.ResultsWe 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.ConclusionOur 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.
Highlights
The somatic cell score (SCS) is implemented in routine sire evaluations in many countries as an indicator trait for udder health
The confidence intervals of the maxima observed in our linkage and linkage disequilibrium analysis (LALD) analysis did not include marker TGLA227 at the telomeric end of Bos taurus autosome 18 (BTA18), and the quantitative trait loci (QTL) position reported by Lund et al [8] as well as the assumption of a second QTL by Xu et al [11] further in the middle of BTA18, indicated that we identified a second QTL for SCS in German Holstein cattle and possibly discovered a third QTL on BTA18 in our studies
Our results suggest that the chromosomal region including interval 9 (HAMP_c.366+109G>A BMS833) and interval 12-13 (BB710 - PVRL2_c.392G>A), in the middle to telomeric region on BTA18 has a strong impact on SCS in the German Holstein population
Summary
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). Several studies have attempted to identify chromosomal regions, genes and polymorphisms that influence udder health in order to improve breeding strategies. SCS has been used as an indicator of udder health and is implemented in routine sire evaluations in many countries [1]. MAS implements genetic marker information of confirmed QTL regions to identify individuals with favourable genetic background concerning the trait of interest.
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