Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

A map of QTL affecting milk production traits in the Italian Holstein-Friesian

The Italian Hostein-Friesian breed is the most important dairy cattle breed in Italy. So far no complete genome scan to identify QTL for milk production traits have been produced. We herein produced for the first time a complete map of QTL affecting milk yield (MY) and protein percentage (PP) in this breed using a selective milk DNA pooling approach in a daughter design.

It was estimated that the genome scan, that was conducted for eight half daughter families using 183 dinucleotide microsatellites distributed on all bovine autosomes (BTA) and the X chromosome, uncovered 35 QTL regions (QTLR) for MY and 32 QTLR for PP (about 1.1 and 1.2 QTLR for each autosome for PP and MY, respectively). For PP, 13 chromosomes (BTA01, BTA04, BTA05, BTA08, BTA09, BTA11, BTA16, BTA18, BTA22, BTA23, BTA24, BTA27 and BTA29) showed a single peak of significance, 5 chromosomes (BTA02, BTA06, BTA13, BTA17 and BTA21) showed two peak of significance and 3 chromosomes showed at least 3 distinct QTLR (BTA03, BTA14 and BTA20). For MY, 12 chromosomes showed only one clear peak of significance (BTA01, BTA02, BTA04, BTA05, BTA10, BTA12, BTA18, BTA19, BTA21, BTA25, BTA28 and BTA29), 6 showed the presence of two QTLR (BTA03, BTA08, BTA11, BTA13, BTA17 and BTA20) and 3 showed at least 3 QTLR (BTA06, BTA07 and BTA14). Moreover, it was estimated that about 95% and 92% of the PP and MY segregating QTL in the Italian Holstein population will have had some opportunity to be identified in the present genome scans.

For PP, taking the averaged substitution effect for the significant markers in each QTLR, allele substitution effect ranged from 0.008 to 0.025 EBV%, with mean 0.013793 EBV% and sum of 0.441379 EBV%. For MY, averaged allele substitution effect ranged from 241,4 to 664,0 kg (Daughter Yield Deviation), with mean 328,2 kg (DYD) and sum of 11487 kg (DYD). Five QTLR (BTA03, BTA11, BTA13, BTA14 and BTA20) were chosen to investigate the effect on other milk production or reproductive traits. In general, significant sire by marker tests were observed for most correlated traits (namely protein yield, fat yield and fat percentage) in the same regions.

No clear association of these five QTLR was evidenced with other traits like milk somatic cell count, calving difficulties and perinatal mortality. Protocols for marker analysis have been developed including new methods for single nucleotide polymorphism allele frequency estimation in milk DNA pools.

New mutations in candidate genes have been obtained. Partial publications of these results (mainly for BTA14 and BTA20) have been produced confirming the presence of QTL already identified by others on these chromosomes but also indicating the presence of additional QTL that may be considered for the use of these QTLR in marker assisted selection plans. Partial results have been illustrated to the final users, namely the Italian Holstein Breeder Association, semen centers and Provincial breeder associations.

The results provided in this study will represent the starting point to further investigate in detail QTLR in order to identify the causative mutations.

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