Abstract
Reduced female fertility could cause considerable economic loss and has become a worldwide problem in the modern dairy industry. The objective of this study was to detect quantitative trait loci (QTL) for female fertility traits in Chinese and Nordic Holsteins using various strategies. First, single-trait association analyses were performed for female fertility traits in Chinese and Nordic Holsteins. Second, the SNPs with P-value < 0.005 discovered in Chinese Holsteins were validated in Nordic Holsteins. Third, the summary statistics from single-trait association analyses were combined into meta-analyses to: (1) identify common QTL for multiple fertility traits within each Holstein population; (2) detect SNPs which were associated with a female fertility trait across two Holstein populations. A large numbers of QTL were discovered or confirmed for female fertility traits. The QTL segregating at 31.4~34.1 Mb on BTA13, 48.3~51.9 Mb on BTA23 and 34.0~37.6 Mb on BTA28 shared between Chinese and Nordic Holsteins were further ascertained using a validation approach and meta-analyses. Furthermore, multiple novel variants identified in Chinese Holsteins were validated with Nordic data as well as meta-analyses. The genes IL6R, SLC39A12, CACNB2, ZEB1, ZMIZ1 and FAM213A were concluded to be strong candidate genes for female fertility in Holsteins.
Highlights
Poor female fertility has become a serious worldwide problem in modern dairy cattle industry, due to its unfavorable genetic correlations with milk yield traits which have gone through intensive selections during the past few decades[1]
24 significant quantitative trait loci (QTL) were detected on 14 different chromosomes for 11 fertility-related traits using Illumina BovineSNP50 BeadChip (54 K) single nucleotide polymorphism (SNP) chip in Danish and Swedish Holsteins[7] and a sharp peak was observed on BTA13 for interval from calving to first insemination
The QTL on BTA4 and BTA13 were further narrowed down by fine mapping using the 54k genotypes imputed to the high density SNP array (Illumina BovineHD BeadChip, 777 K) and further to whole genome sequence variants[10, 11]
Summary
Poor female fertility has become a serious worldwide problem in modern dairy cattle industry, due to its unfavorable genetic correlations with milk yield traits which have gone through intensive selections during the past few decades[1]. Previous studies performed in dairy cattle on growth[14] and longevity[15] traits have already shown that novel QTL were detected using meta-analysis across populations. Bolormaa et al.[16] showed that the detection power, which was measured by numbers of SNPs validated in an independent population, for stature, fatness and reproduction in beef cattle was increased using meta-analysis for multiple traits within population. In 2015, a joint GWAS for milk fatty acid traits was performed using Illumina BovineHD BeadChip markers from 784 Chinese and 371 Danish Holstein cows, a large number of additional significant SNPs were detected[19].
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