Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

A map of QTL affecting milk production traits in the Simmental/Red Holstein Cross

The recent experiments using advanced backcross QTL strategy (AB-QTL) in plant breeding showed that even wild progenitor species constitute a prominent source of still unfolded variability for complex traits in lines, which have been cultivated for over 8000 years.

These studies indicated the local and global importance of genetic variability in presently less modern breeds or lines. AB-QTL is one of the strategies to harness hidden potential and broaden the genetic diversity of the existing gene pool. Over the last quarter of a century German-Austrian Fleckvieh breeders designed a large advanced backcross population, which is embedded within the purebred Fleckvieh (FV).

Utilization of Red Holstein (RH) founders as donors in interbreed crosses was the strategy to introgress valuable traits/genes from the donor breed (RH) into the existing gene pool of the FV breed. The FV breeders used the advanced backcross method primarily to introgress quantitative trait loci relating to two complex traits and their components: Milk Yield and Udder Quality.

Most FV breeders wanted only the desired part of the genome of the RH population to be introgressed into that of the FV population, whilst the remaining genome of the FV population should be kept intact as much as possible.

The aim of this study was to use DNA marker based strategies to
- Simultaneously detect quantitative trait loci relating to milk yield (MY) and milk protein percentage (PP) in purebred FV and in the Advanced Backcross Fleckvieh (ABFV) population,
- To set up necessary information for marker assisted selection (MAS) regardless of allele origin and
- To prepare information for marker assisted accumulation of positive alleles and selection against undesired alleles introgressed by the most important donor founder.

For a whole genome scan in the ABFV population we sampled a large daughter design with eight half-sib families. The average family size was 2134 daughters, ranging from 1470 to 3329 per family. From 17073 stored milk samples we prepared selective DNA pools for nine traits: MY, PP, milk protein yield (PY), milk fat percentage, milk fat yield, milk somatic cell count, maternal fertility, calving difficulty, and stillbirth.

The selection criteria for pooling were corrected breeding values calculated from the routinely performed, common genetic evaluation for South-Germany and Austria. Each pool replicate consists of 101.5 the most extreme daughters. The whole genome scan was performed for two traits MY and PP using the same set of 220 microsatellite markers used for QTL mapping in purebred Bavarian-Austrian Fleckvieh too. Totally 9011 pool genotypes were produced and combined into 2034 single marker tests. Similarly as for purebred Fleckvieh two families sampled in Austria showed a higher proportion of inconsistent pool genotype results due to systematic sampling error.

Therefore we excluded these two families from all further analysis. According to results of adjusted false discovery rate and approximate interval mapping analysis we detected 22 QTL regions (QTLR) segregating in six advanced backcross families.

Most of the detected QTL affect both PP and MY simultaneously but with higher significance for one of the two traits. There are five PP-QTL which are partly independent of MY: BTA14 central, BTA24, BTA25, BTA28 and BTA29. Ten QTLR (BTA01, BTA02, BTA04, BTA05, BTA06, BTA07, BTA08, BTA09, BTA10, and BTA19) showed effects for both traits but higher significance for PP. The remaining seven QTLR showed effects for both traits but higher significance for MY: BTA03, BTA11, BTA12, BTA16, BTA22, BTA23 and BTA26.

According to the haplotype analysis in a complex pedigree including all family sires as well as all available ancestors and the founder of the ABFV population there are some indications for the introgression of the active QTL variants by the Red Holstein founder into the ABFV population. The QTL affecting MY and PP and segregating on the proximal region of BTA10 is most possibly introgressed by Red Holstein founder.

Additional to BTA10 there were some indications for introgressed active QTL variants on BTA01 BTA05, BTA19 and BTA28. For these four QTL regions we observed the significant QTL effects in the purebred Fleckvieh families too. The estimated QTL positions are rather inaccurate, thus it is not possible to make a clear conclusion about introgression but our results provide valuable starting information for running follow up studies aiming at the confirmation by interval mapping, use for fine mapping and marker assisted selection. Partial results have been presented to the final users, namely the Bavarian-Austrian Fleckvieh Breeder Associations and artificial insemination stations. These agreed on a program for implementation of the mapping results into marker assisted selection.

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