PSIX-20 - Differential gene expression in peripheral white blood cells of fertile and sub-fertile beef heifers

Abstract: Infertility in beef heifers remains a major economic loss to the cow-calf production industry. Identifying beef heifers with superior genetic potential for improved fertility would increase profitability. Therefore, the study aimed to identify differences in transcriptome profile from peripheral white blood cells (pWBCs) of beef heifers with varying reproductive potential. To accomplish this, Angus-Simmental crossbred heifers were subjected to an estrus synchronization and fixed-time artificial insemination (AI) protocol (7-Day CO-Synch + CIDR). Fourteen days after AI, all heifers were exposed to fertile bulls for a 60-day natural breeding season. Depending on the presence or absence of conceptus 120 days post-AI, heifers were classified as fertile (pregnant heifers) or sub-fertile (non-pregnant by AI or bull-breeding). Pregnancies were terminated, and all animals in both groups were cycling when pWBCs were isolated. Total RNA was extracted from the PWBCs and subjected to the library preparation and sequencing on the Nova-Seq platform. The read counts were obtained after data filtering and quality control using FastQC v0.11.9 and MultiQC v1.12 and alignment to the Ensemble’s ARS UCD1.2 Bos taurus genome reference using STAR aligner v2.7.5 for fertile (n = 8) and sub-fertile (n = 5) beef heifers. The filtered data were subjected to differential expression analysis using DESeq2. We identified 300 significantly differentially expressed genes (DEGs) with p-value ≤ 0.05 and absolute (log2 fold change) ≥ 0.5. Among them, 34 genes including FKBP5, ADCY3, REPS1, LAMP1, CTSH, ADGRE5 were identified with padj < 0.05. DEGs were over-represented for pathways such as response to thyroid stimulus, immune response, response to lipid, neutrophil degranulation, and calcium ion binding. Some of these genes were reported as fertility-related, while the other genes are novel and have the potential to predict heifers with varying reproductive potential. A detailed understanding of the underlying biological mechanisms of the top genes and a follow-up study with a higher sample size at different time points could validate the potential candidates identified in this study.