Short Communication: Detection of Quantitative Trait Loci Influencing Somatic Cell Score in Spanish Churra Sheep

Abstract

Eleven half-sib ovine families, including 1,421 Spanish Churra ewes, were analyzed for 181 microsatellite markers spanning the entire autosomic ovine genome. Using a multimarker regression method, a daughter experimental design was used to identify putative quantitative trait loci (QTL) affecting the somatic cell score (SCS). Chromosome-wise significance thresholds were set empirically by permuting the phenotypic data. Marker order and genetic distances of the autosomic linkage map built for this commercial population were in accordance with the published ovine linkage map. An across-family association analysis revealed a region on chromosome 20 suggestive of evidence for a QTL. Segregation of the QTL into 2 families was inferred from the within-family analysis, and differences in the position of the suggested QTL were found between the 2 half-sib groups. This could be the result of incomplete information associated with the markers for the significant families. The location of the major histocompatibility complex in proximity to the across-family effect suggests this region may harbor a segregating QTL for the SCS in the Churra population. Studies in dairy cattle examining the SCS have reported linkage associations on corresponding bovine orthologous regions, supporting the validity of our findings.

Genetic selection for reduced somatic cell counts in sheep milk: A review

“…At present, however, the available literature on GS and molecular markers for mastitis resistance mainly refer to dairy cattle (Klungland et al, 2001;Boichard et al, 2003;Schulman et al, 2004). In sheep, quantitative trait loci (QTL) influencing SCS have recently been detected (Rupp et al, 2003b;Gutierrez-Gil et al, 2007;Raadsma et al, 2009).…”

Detection of QTL Underlying Milk Traits in Sheep: An Update

“…Different methods have been used, however, to take into account the testing for 26 chromosomes in the genome scans reported. Hence, Bonferroni corrections have been used in some of the cases such as Churra sheep analysis of SCS (Gutiérrez-Gil et al, 2007), and the Sarda X Lacaune population . Following the method described by Harmegnies et al (2006) genome-wide permutations were implemented in the Churra sheep analysis for milk production traits (Gutiérrez-Gil et al, 2009a), In addition to the genome-wise significant QTL, these authors also considered the genome-wise suggestive linkage level, for which one false positive is expected in a genome scan (Lander & Kruglyak, 1995).…”

“…This analysis method is the one followed for milk traits QTL mapping in the commercial sheep populations previously described. The analyses performed in Spanish Churra sheep were performed using HSQM (Coppieters et al, 1998) which implements the multimarker regression method described by Knott et al (1996) (Díez-Tascón et al, 2001;Gutiérrez-Gil et al, 2007, 2009a. In the Lacaune and Manech French populations, the QTL detection was carried out according to the methodology proposed by Knott et al (1996) and Elsen et al (1999) by within-sire linear regression .…”

“…YDs are weighted averages of ewe's lactation yields minus solutions for management group, herd-sire, and permanent environmental effects (VanRaden & Wiggans, 1991). These are the quantitative measures that have been used in the QTL mapping experiments performed in Churra sheep (Díez-Tascón et al, 2001;Gutiérrez-Gil et al, 2007;2009a). Because rams do not have yield deviations, DYD, which are adjusted for mates´ merit, can provide a usefull, unregressed measure of daughter performance to use in grand-daughter designs (VanRaden & Wiggans, 1991).…”

“…A total of 1421 ewes sired by 11 IA rams and distributed among 17 different flocks were used in this project for detection of QTL underlying classical milk traits (Gutiérrez-Gil et al, 2009a). Other traits of interest in dairy sheep production such as morphology traits (Gutiérrez-Gil et al, 2008; and resistance to mastitis and nematode gastrointestinal infections (Gutiérrez-Gil et al, 2007;2009b) were also recorded in the commercial population genotyped. The average family size in this daughter design was around 110, ranging from 47 to 223 daughters per sire.…”