Höglund Johanna K, Guldbrandtsen Bernt, Lund Mogens S, Sahana Goutam
Department of Molecular Biology and Genetics, Center for Quantitative Genetics and Genomics, Aarhus University, P.O. Box 50, 8830, Tjele, Denmark.
Present address: Department of Animal Science, Aarhus University, P.O. Box 50, 8830, Tjele, Denmark.
BMC Genet. 2015 Jun 3;16:60. doi: 10.1186/s12863-015-0210-3.
Female fertility is an important trait in cattle breeding programs. In the Nordic countries selection is based on a fertility index (FTI). The fertility index is a weighted combination of four female fertility traits estimated breeding values for number of inseminations per conception (AIS), 56-day non-return rate (NRR), number of days from first to last insemination (IFL), and number of days between calving and first insemination (ICF). The objective of this study was to identify associations between sequence variants and fertility traits in Jersey cattle based on 1,225 Jersey sires from Denmark with official breeding values for female fertility traits. The association analyses were carried out in two steps: first the cattle genome was scanned for quantitative trait loci using a sire model for FTI using imputed whole genome sequence variants; second the significant quantitative trait locus regions were re-analyzed using a linear mixed model (animal model) for both FTI and its component traits AIS, NRR, IFL and ICF. The underlying traits were analyzed separately for heifers (first parity cows) and cows (later parity cows) for AIS, NRR, and IFL.
In the first step 6 QTL were detected for FTI: one QTL on each of BTA7, BTA20, BTA23, BTA25, and two QTL on BTA9 (QTL9-1 and QTL9-2). In the second step, ICF showed association with the QTL regions on BTA7, QTL9-2 QTL2 on BTA9, and BTA25, AIS for cows on BTA20 and BTA23, AIS for heifers on QTL9-2 on BTA9, IFL for cows on BTA20, BTA23 and BTA25, IFL for heifers on BTA7 and QTL9-2 on BTA9, NRR for heifers on BTA7 and BTA23, and NRR for cows on BTA23.
The genome wide association study presented here revealed 6 genomic regions associated with FTI. Screening these 6 QTL regions for the underlying female fertility traits revealed that different female fertility traits showed associations with different subsets of the individual FTI QTL peaks. The result of this study contributed to a better insight into the genetic control of FTI in the Danish Jersey.
母牛繁殖力是奶牛育种计划中的一个重要性状。在北欧国家，选择是基于繁殖力指数（FTI）。繁殖力指数是四个母牛繁殖力性状估计育种值的加权组合，这四个性状分别是每次受孕的授精次数（AIS）、56天不返情率（NRR）、首次授精到最后一次授精的天数（IFL）以及产犊到首次授精的天数（ICF）。本研究的目的是基于来自丹麦的1225头具有母牛繁殖力性状官方育种值的泽西种公牛，鉴定泽西牛序列变异与繁殖力性状之间的关联。关联分析分两步进行：首先，使用插补的全基因组序列变异，通过FTI的父系模型对牛基因组进行数量性状基因座扫描；其次，使用线性混合模型（动物模型）对FTI及其组成性状AIS、NRR、IFL和ICF重新分析显著的数量性状基因座区域。对于AIS、NRR和IFL，分别对小母牛（头胎母牛）和母牛（经产母牛）的潜在性状进行了分析。
第一步检测到6个与FTI相关的QTL：分别位于BTA7、BTA20、BTA23、BTA25上各有1个QTL，在BTA9上有2个QTL（QTL9-1和QTL9-2）。第二步中，ICF与BTA7、BTA9上的QTL9-2、BTA9上的QTL2以及BTA25上的QTL区域相关联，BTA20和BTA23上的母牛AIS、BTA9上QTL9-2处的小母牛AIS、BTA20上的母牛IFL、BTA23和BTA25上的母牛IFL、BTA7上的小母牛IFL以及BTA9上QTL9-2处的小母牛IFL、BTA7和BTA23上的小母牛NRR以及BTA23上的母牛NRR相关联。
本文提出的全基因组关联研究揭示了6个与FTI相关的基因组区域。对这6个QTL区域进行潜在母牛繁殖力性状筛查发现，不同的母牛繁殖力性状与各个FTI QTL峰值的不同子集相关联。本研究结果有助于更好地了解丹麦泽西牛中FTI的遗传控制。
