부산대학교 도서관

Current conception rates in U.S. Holstein heifers are estimated to be between 55 and 60%. The objective here was to identify genomic loci associated with fertility in Holstein dairy heifers. Breeding and health records of Holstein heifers were analyzed from a commercial dairy heifer raising facility in southern Idaho. All heifers were bred by AI at observed estrus, and pregnancy was determined at Day 35 after AI via palpation. Records analysis identified 497 heifers that could be classified as highly fertile (HF) due to conceiving on first AI service and 429 subfertile (SF) that did not conceive until after fourth AI service or were culled due to failure to conceive. Deoxyribonucleic acid was extracted from blood samples and genotyped using the Illumina Bovine HD BeadChip. Quality control consisted of removing animals with <90% of genotypes and removing markers with <90% of genotypes or a minor allele frequency <1% or if they failed Hardy–Weinberg equilibrium testing. A total of 466 HF and 368 SF heifers and 590,904 SNP remained for the analysis. A genomewide associated analysis (GWAA) was conducted using an additive model of the efficient mixed-model association expedited statistical test with a genomic relationship matrix. Covariates used in the analysis accounted for relatedness (identity by descent ≥ 0.2) of heifers and the AI bull the heifer was bred to as conception rates differed between AI sires (P< 6.9 × 10−13). The GWAA identified 153 SNP representing 147 QTL (P< 5.5 × 10−5) that were moderately associated and 34 SNP representing 26 QTL (P< 5.5 × 10−7, proportion variance explained ranged from 0.032 to 0.115) that were strongly associated with heifer fertility. Pseudo-heritability was estimated to be 0.46 and l = 0.98. These results indicate that there is ample opportunity to make significant gains in fertility in Holstein heifers with genomic selection. This project was supported by Agriculture and Food Research Initiative Competitive Grant number 2013-68004-20365 from the USDA National Institute of Food and Agriculture.