SHEEPMILKGENES · High resolution mapping of a QTL region influencing fat percentage in Spanish Churra dairy sheep

High resolution mapping of a QTL region influencing fat percentage in Spanish Churra dairy sheep.

This project has aimed the identification of candidate genes for a QTL region previously identified in a genome scan study performed in Spanish Churra sheep (Gutiérrez-Gil et al. 2009). The initial targeted QTL was located on OAR20 and influenced milk fat percentage. Due to the similar efforts required for the analysis of other regions, the study of another QTL region located on OAR3 and influencing milk protein percentage was included as an additional target QTL region of the project. The results derived from the defined work packages can be summarised as follows: WP1) The segregation of the two target QTL was confirmed by analysing a new sampling population, which included a total of 841 Churra ewes belonging to 15 half-sib families (Population 2). WP2) Twelve markers for OAR3 and one marker (due to technical problems) for OAR20 were additionally genotyped across Population 2. Because of statistical power limitation we analysed a new larger population (Population 3), which involved 1,661 animals from 14 half-sib families. The increased marker density reached on OAR3, allowed the implementation of a LDLA analysis, which narrowed the CI for this chromosome to a 13 cM-long region. The refinement of the OAR20 QTL was postponed due to the limited number of markers of the reference linkage map in the region of interest. WP3) We selected prolactin (PRL) and alpha-lactalbumin (LALBA) genes as strong positional and functional candidate genes for the OAR20 and OAR3 QTL respectively. By analysing the sires of Population 2, we identified 33 and 31 SNP markers in these genes respectively. Exploratory linkage and association analyses performed for some of these SNP markers in relation to milk production traits suggested that it is unlikely that the PRL gene is underlying the OAR20 QTL. The results obtained for the LALBA gene are being compiled for publication. WP4) High-density fine-mapping based on SNP-array genotyping. Joining funding resources from the Spanish Ministry of Science and Innovation (Project AGL2009-07000), a high-density SNP genotyping has been performed on the target QTL regions using the Ovine SNP50BeadChip (Illumina, Inc). After the quality control performed a total of 4166 and 929 SNP markers have been analysed for OAR3 and OAR20 respectively. The results are also being compiled for publication. WP5) Technology transfer: The possible implementation of the project outputs into the classical breeding scheme of Churra sheep is being assessed by the researchers involved in this project and the leader of the breeding scheme together with the Churra association breeders. Due to the high statistical support obtained for the OAR3 QTL influencing PP in the analysis based on the high-density SNP genotyping further research efforts will be focused on trying to identify the allelic variant underlying this QTL. If achieved, the identification of the causal mutation or QTN may serve to directly implement molecular information into the Churra sheep breeding program and increase the response to selection for milk protein percentage. This trait has a direct influence on cheese yield, and therefore the identification of the causal gene could be of great interest for the dairy sheep industry. This project as a whole has tried to identify genetic markers that influence the variability observed in milk production traits of Spanish Churra sheep. This breed is the prevalent autochthonous breed of the region of Castilla and León. Because of its rusticity Churra sheep is very well adapted to the extreme clconditions of its geographical range of distribution. Hence, trying to improve milk production traits in Churra the SheepMilkGenes project may be considered to provide a positive socio-economic impact on the livestock sector of the region where the host institution is located as well as on the preservation of sustainable production systems that help to maintain the rural areas of the region of Castilla and León.

Data: CORDIS, © European Union