New breeding tools for improving mastitis resistance in European dairy cattle
Milk production is the most important agricultural activity in the EU. In dairy cattle, mastitis is the most common and costly disease, and the cause of the highest antibiotic use in livestock. Mastitis incidence should have declined with improved methods of prevention and treatment, but it has not. The heritability for welfare traits are low and hence genetic improvement based on phenotypic selection is difficult. The application of genotype-based marker-assisted selection would give the European dairy industry new opportunities for the genetic improvement of mastitis resistance.
Quantitative trait loci (QTL) influencing economically important traits in livestock can be detected by whole genome scans. The next step is to move towards more precise localisation of the genes controlling the trait. Mapping of QTL using existing populations is restricted to the traits recorded in each population. Due to extensive recording of health and fertility traits, the Nordic countries provide a unique resource for developing of breeding tools for the improvement of key functional traits in dairy cattle. Genome scans have shown that QTL for mastitis resistance segregate in the Nordic cattle populations.
The overall objective of the project is to confirm, fine-map and identify genetic loci (quantitative trait loci, QTL) harbouring genes underlying variation in mastitis resistance in dairy cattle. The specific objectives are:
1) to combine separate putative linkage mapping results into a multi-population analysis
2) to develop statistical methodology to fine map multiple trait QTL
3) to generate dense marker maps for confirmed QTL regions
4) to identify marker haplotypes associated with specific QTL alleles (for marker assisted selection)
5) to dissect the genetic basis of mastitis further by analysing pathogen specificity and pleiotropic effects of the QTL
6) to develop statistical methodology for introgression of favourable QTL alleles to new populations.
Progress to Date
During the second project year several of the objectives have been reached.
1) Sires segregating for confirmed and refined QTL-intervals have been selected. The data was analysed including multiple trait variance components across countries and linkage/linkage disequilibrium. The decision on the chromosome regions to be fine-mapped (for which dense marker maps are developed) was based on these results.
2) The statistical methodology was improved by assessing problems encountered with haplotype reconstruction, presence of null alleles, missing genotypes and missing pedigree information.
3) Dense marker maps including new micro-satellites and newly generated SNPs in candidate genes were developed for two regions. The development continues with adding more markers to these regions and working on two additional regions.
4) Fine-mapping of the first selected region was started using LA/LD analyses; including multiple traits and longitudinal information where appropriate. A narrow 4-marker haplotype was identified for the region, which can be utilised in further analyses.
Scientist responsible for the project
Dr JOHANNA VILKKI
Finland - FI
Phone: +358 3 4188 3669
Fax: +358 3 4188 3618
||MTT Agrifood Research Finland
||01 October 2002
||3 631 735 €
|Total EC contribution
||2 038 020 €
|Web address of the project