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BOVMAS Sintesi della relazione

Project ID: QLK5-CT-2001-02379
Finanziato nell'ambito di: FP5-LIFE QUALITY
Paese: Austria

Use of MAS in cattle populations with complex breeding goals

The aim of this comprehensive simulation study was a genetic and economic evaluation of applying marker assisted preselection (MAPS) in a realistic dairy cattle breeding program with a complex breeding goal composed of the 4 correlated traits - milk yield (MY), protein percent (PP), female fertility (FF) and somatic cell count (SCC). A complex genome was created and evolved by natural and artificial selection, aiming at a realistic distribution of the genetic variance among QTL.

Furthermore, a QTL mapping experiment was carried out applying selective DNA pooling. Detected QTL were fine mapped and effects on single traits and the index value were estimated. Subsequently, a realistic breeding program was simulated, in which selection was performed according to ?conventional breeding values, without the use of embryo transfer, which was compared with MAPS of test sire candidates among full-sibs generated by embryo transfer.

MAPS was applied as bottom up approach. For a constant test capacity the number of test sires was varied from 56, 80 to 168 with 150, 100 and 50 daughters per sire, respectively. To evaluate the impact of the success rate of embryo transfer on the genetic gain per generation, MAPS schemes with 2 and 4 male full-sibs were simulated. It was shown that MAPS could increase the competitiveness of breeding programs in dairy cattle breeding programs with complex breeding goals.

The simulated MAPS designs showed, due to the higher proportion of segregating QTL detected among elite sires, an improved efficiency with more daughters per test sire. Nevertheless, the selection steps following preselection of test sires, such as selection of proven sires and elite sires, yielded higher genetic gain in the population with smaller daughter groups and more test sires progeny tested. These opposite trends need to be optimised in an economic evaluation, which accounts for discounted return and costs. Genetic gain per generation in MAPS schemes for test sires entering progeny testing were remarkably increased compared to selection based on conventional breeding values in MY (1 to 27% across evaluated schemes) while the negative genetic trends in PP, as observed in the selection based on conventional breeding values, increased slightly. Genetic trends of FF and SCC in MAPS did not change substantially, compared to selection based on conventional breeding values.

The economic implications of MAPS among full-sibs and extra genetic benefits from MAPS compared to selection according to conventional breeding values were modelled with ZPLAN, a deterministic simulation program. Parameters used for the economic evaluation were annual monetary genetic gain (AMGG), discounted returns, discounted costs and discounted profit. Extra AMGG from MAPS, was moderate and mainly obtained in MY while the negative trend in PP, as observed in the conventional breeding schemes, increased slightly. AMGG increased between 5 and 9%, dependant on the evaluated MAPS scheme.

When test capacities were constant, the bottom up approach favoured, with regard to AMGG, large daughter groups (150 daughter records per test sire), while the selection stages applied to test sires after preselection were more efficient with a larger number of test sires. Since discounted costs increased when more test sires were evaluated each year, the highest discounted profit in breeding value assisted selection was obtained with 80 test sires.

The same number of test sires with four male full-sibs per embryo transfer available for preselection was the best MAPS scheme. Extra costs of MAPS were moderate compared to costs of the progeny testing breeding program, and partly reduced due to increased selection intensity among elite dam candidates.

An additional simulation was based on the real population structure of the Italian, Austrian and German Brown breed, using the 5 QTL with largest allele substitution effect for MY identified in the genome scan. The use of embryonic technologies such as Multiple Ovulation and Embryo Transfer is a determinant for a successful MAPS since it allows choosing superior young bulls out of a set of full brothers (advantages increase with increasing number of full sibs). As expected the overall advantage of MAPS based on 5 QTL influencing a single production trait evaluated with respect to the genetic gain achieved in a complex breeding goal is smaller as compared to its advantage on a single trait.

The results of these simulation studies can be used as indicators of the genetic gains to be expected by applying different scenarios of MAPS, for the Brown Swiss dairy cattle population in Italy and in Europe based on 5 QTL as found in the BovMAS project and the ultimate genetic and economic gains to be expected in a dairy cattle population with approximately 50.000 cows under milk recording by making use of all genetic variance, which was also traceable via segregation analysis to the test sires.

Informazioni correlate


Johann SOELKNER, (Head of Unit)
Tel.: +43-1-476543271
Fax: +43-1-476543254