Genomic and phenotypic analyses of antral follicle count in Aberdeen Angus cows
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Antral follicle count (AFC) was phenotypically and genetically evaluated in a Bos taurus cow population. A total of 257 Aberdeen Angus cows underwent an ovarian ultrasound evaluation and hormonal synchronization for timed artificial insemination (TAI). These animals were between 40 and 70 d postpartum with a body score condition (BSC) between 2 and 4 (average = 2.7) on a scale of 1–5. The number of antral follicles was assessed 10 d before (D-10) the beginning of TAI. Visible follicles (≥3 mm in diameter) were counted from both ovaries (right and left) to determine the number of total follicles, and animals were allocated into groups according to the number of antral follicles: low AFC was defined as ≤ 15 follicles (n = 93); intermediate AFC as < 24 follicles and >16 follicles (n = 97); and high AFC as ≥ 25 follicles (n = 67). The comparison between the average AFC and pregnancy rate was performed using the chi-square test in the Minitab® 19.2 statistical software, adopting a P-value ≤ 0.05. Hair samples of Aberdeen Angus cows were collected for genomic DNA extraction and subsequent genotyping analysis using the GGP HD array. The associations between SNP markers and phenotypic information (AFC) were determined using the GBLUP methodology. Windows explaining more than 1% of the total additive genetic variance were selected as candidates for functional prospection using QTL colocalization and enrichment analysis using a hypergeometric test. The GWAS identified seven candidate genomic windows and 54 annotated genes within them. Among these genes, DUSP1, SOX17, XKR4, PLAG1, HFM1, PPM1K, IBSP, NCAPG-LCORL, and HMGHZ were associated with biological processes that might be related to follicle count in Angus cows. Enrichment analysis of the reproduction-related traits found enriched QTLs in BTA5 (“Inhibin level”, “Insulin-like growth factor 1 level”), BTA6 (“Calving ease”, “Calf size”, “Calving index”), and BTA14 (“Insulin-like growth factor 1 level”; “Age at puberty”, “Interval to first estrus after calving”). This study brings new knowledge of the genomic background of AFC and may lead to further investigations regarding physiological explanations for different AFCs and their relationship to fertility.
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