Quantitative trait loci affecting calving traits in Danish Holstein cattle.

The objectives of this study were 1) to detect quantitative trait loci (QTL) affecting direct and maternal calving traits at first calving in the Danish Holstein population, 2) to distinguish between pleiotropic and linked QTL for chromosome regions affecting more than one trait, and 3) to detect QTL affecting stillbirth and calving difficulties but not calf size that could be used in selection to improve calving performance. Progeny-tested sons (2,297) were genotyped for 356 microsatellites in 34 grandsire families on all 29 autosomes. A total of 27 significant QTL on 17 chromosomes were detected using a between-families linear regression model. For the direct calving traits, 4 QTL significantly affected calving difficulty, 5 QTL affected stillbirth, and 7 QTL affected calf size subjectively assessed by the farmer as a categorical trait. When the maternal components of the same traits were tested, there were significant effects of 3 QTL on calving difficulty, 6 QTL on stillbirth, and 2 QTL on calf size. The variance component mapping approach was used to estimate the relative posterior probability of linkage and pleiotropic models. The most probable model indicated a pleiotropic QTL on chromosome 12 and 25 and a linked QTL on chromosome 7 and 26. Chromosome 18 seemed to harbor a QTL with a pleiotropic effect on the direct calving traits and linked to maternal stillbirth. Markers on chromosomes 3, 4, 7, 10, 12, 18, 21, 24, 26, and 28 can be used to select new breeding candidates to produce daughters with more efficient calving performance.

Thomasen JR ，Guldbrandtsen B ，Sørensen P ，Thomsen B ，Lund MS ... -  《-》

Quantitative trait loci mapping of calving and conformation traits on Bos taurus autosome 18 in the German Holstein population.

Linkage, linkage disequilibrium, and combined linkage and linkage disequilibrium analyses were performed to map quantitative trait loci (QTL) affecting calving and conformation traits on Bos taurus autosome 18 (BTA18) in the German Holstein population. Six paternal half-sib families consisting of a total of 1,054 animals were genotyped on 28 genetic markers in the telomeric region on BTA18 spanning approximately 30 Mb. Calving traits, body type traits, and udder type traits were investigated. Using univariately estimated breeding values, maternal and direct effects on calving ease and stillbirth were analyzed separately for first- and further-parity calvings. The QTL initially identified by separate linkage and linkage disequilibrium analyses could be confirmed by a combined linkage and linkage disequilibrium analysis for udder composite index, udder depth, fore udder attachment, front teat placement, body depth, rump angle, and direct effects on calving ease and stillbirth. Concurrence of QTL peaks and a similar shape of restricted log-likelihood ratio profiles were observed between udder type traits and for body depth and calving traits, respectively. Association analyses were performed for markers flanking the most likely QTL positions by applying a mixed model including a fixed allele effect of the maternally inherited allele and a random polygenic effect. Results indicated that microsatellite marker DIK4234 (located at 53.3 Mb) is associated with maternal effects on stillbirth, direct effects on calving ease, and body depth. A comparison of effects for maternally inherited DIK4234 alleles indicated a favorable, positive correlation of maternal and direct effects on calving. Additionally, the association of maternally inherited DIK4234 marker alleles with body depth implied that conformation traits might provide the functional background of the QTL for calving traits. For udder type traits, the strong coincidence of QTL peaks and the position of the QTL in a region previously reported to harbor QTL for somatic cell score indicated that effects of QTL for udder type traits might be correlated with effects of QTL for udder health traits on BTA18. Our results suggest that loci in the middle to telomeric region on BTA18 with effect on conformation traits may also contribute to the genetic variance of calving and udder health traits. Further analyses are required to identify the causal mutations affecting conformation and calving traits and to investigate the correlation of effects for loci associated with conformation, calving, and udder health traits.

Brand B ，Baes C ，Mayer M ，Reinsch N ，Seidenspinner T ，Thaller G ，Kühn Ch ... -  《-》

Genome-wide association study for calving traits in Danish and Swedish Holstein cattle.

A total of 22 quantitative trait loci (QTL) were detected on 19 chromosomes for direct and maternal calving traits in cattle using a genome-wide association study. Calving performance is affected by the genotypes of both the calf (direct effect) and dam (maternal effect). To identify the QTL contributing these effects to calving characteristics, we performed a genome-wide association study using a mixed-model analysis in Danish and Swedish Holstein cattle. The analysis incorporated 2,062 progeny-tested bulls, and 36,387 single nucleotide polymorphism markers on 29 bovine autosomes were analyzed for association with 14 calving traits. Strong evidence for the presence of QTL that affect calving traits was observed on chromosomes 4, 6, 12, 18, 20, and 25. The QTL intervals were generally smaller than those described in earlier linkage studies. The identification of calving trait-associated single nucleotide polymorphisms and mapping of the corresponding QTL in small chromosomal regions will facilitate the search for candidate calving performance genes and polymorphisms.

Sahana G ，Guldbrandtsen B ，Lund MS 《-》

Detection of quantitative trait loci affecting milk production, health, and reproductive traits in Holstein cattle.

We report putative quantitative trait loci affecting female fertility and milk production traits using the merged data from two research groups that conducted independent genome scans in Dairy Bull DNA Repository grandsire families to identify quantitative trait loci (QTL) affecting economically important traits. Six families used by both groups had been genotyped for 367 microsatellite markers covering 2713.5 cM of the cattle genome (90%), with an average spacing of 7.4 cM. Phenotypic traits included PTA for pregnancy rate and daughter deviations for milk, protein and fat yields, protein and fat percentages, somatic cell score, and productive life. Analysis of the merged dataset identified putative quantitative trait loci that were not detected in the separate studies, and the pregnancy rate PTA estimates that recently became available allowed detection of pregnancy rate QTL for the first time. Sixty-one putative significant marker effects were identified within families, and 13 were identified across families. Highly significant effects were found on chromosome 3 affecting fat percentage and protein yield, on chromosome 6 affecting protein and fat percentages, on chromosome 14 affecting fat percentage, on chromosome 18 affecting pregnancy rate, and on chromosome 20 affecting protein percentage. Within-family analysis detected putative QTL associated with pregnancy rate on six chromosomes, with the effect on chromosome 18 being the most significant statistically. These findings may help identify the most useful markers available for QTL detection and, eventually, for marker-assisted selection for improvement of these economically important traits.

Ashwell MS ，Heyen DW ，Sonstegard TS ，Van Tassell CP ，Da Y ，VanRaden PM ，Ron M ，Weller JI ，Lewin HA ... -  《JOURNAL OF DAIRY SCIENCE》

Detection of quantitative trait loci in Danish Holstein cattle affecting clinical mastitis, somatic cell score, udder conformation traits, and assessment of associated effects on milk yield.

The aim of this study was to 1) detect QTL across the cattle genome that influence the incidence of clinical mastitis and somatic cell score (SCS) in Danish Holsteins, and 2) characterize these QTL for pleiotropy versus multiple linked quantitative trait loci (QTL) when chromosomal regions affecting clinical mastitis were also affecting other traits in the Danish udder health index or milk production traits. The chromosomes were scanned using a granddaughter design where markers were typed for 19 to 34 grandsire families and 1,373 to 2,042 sons. A total of 356 microsatellites covering all 29 autosomes were used in the scan. Among the across-family regression analyses, 16 showed chromosome-wide significance for the primary traits incidence of clinical mastitis in first (CM1), second (CM2), and third (CM3) lactations, and SCS. Regions of chromosomes 5, 6, 9, 11, 15, and 26 were found to affect CM and regions of chromosomes 5, 6, 8, 13, 22, 23, 24, and 25 affected SCS. Markers on chromosomes 6, 11, 15, and 26 can be used to perform marker-assisted selection on CM without a direct negative selection on milk yield, because no effects were detected on the milk traits. Comparing multi-trait models assuming either a pleiotropic QTL affecting 2 traits or 2 QTL each affecting 1 trait gave some evidence to distinguish between these models. For Bos taurus autosome 5, the most likely models were a pleiotropic QTL affecting CM2, CM3, and SCS, and a linked QTL affecting fat yield index. For Bos taurus autosome 9, the most likely model is a pleiotropic QTL affecting CM1 and CM2 at approximately 8 cM.

Lund MS ，Guldbrandtsen B ，Buitenhuis AJ ，Thomsen B ，Bendixen C ... -  《-》