| dc.description.abstract | The reproductive efficiency of Bos taurus beef cattle is pivotal for the profitability and sustainability of cattle operations. Subfertility represents a significant economic burden within the cow-calf sector of the beef industry, with various factors contributing to this issue. Causes contributing to subfertility are often multifaceted including uterine, ovarian, and endocrine disorders. Elusive factors affecting fertility can include dysregulation of the hypothalamic-pituitary-gonadal axis, inadequate uterine receptivity, impaired ovarian function, and ovarian health with the latter playing a critical role in determining fertility status.
While advancements in reproductive technologies have improved the overall success rate during a heifer's first breeding season there remains a persistent population that fails to become pregnant. Due in part to the multifaceted nature of reproductive phenotypes, the majority of heifer reproductive failure remains unexplained. Comparing molecular markers in reproductively divergent heifers holds the potential to improve our knowledge of the causation of reproductive failure. Across this thesis, we have compared reproductively successful heifers to heifers that failed to become pregnant using molecular methods.
A total of 123 cross-bred Angus-Simmental heifers were selected for this study. The heifers underwent an estrus synchronization (ES) and artificial insemination (AI) protocol (7-Day CO-Synch + CIDR). Fourteen days following AI, they were then housed with a fertile bull for 60 days. Pregnancy was determined by ultrasound and rectal palpation performed by a veterinarian 42 days post-AI and one last time 116 days post-AI. Heifers that conceived through AI were classified as fertile (n=8), while those that failed to conceive post-AI and during a subsequent 60-day natural breeding period were classified as subfertile (n=5). Pregnancies were terminated and the heifers resumed normal estrous cyclicity prior to samples being harvested. Both fertile and subfertile heifers were harvested at the Auburn University Lambert-Powell Meats Lab, where samples were collected, transported, and stored for further analysis.
The first study within this thesis focused on exploring differential gene expression in beef heifers by conducting a transcriptomic analysis of peripheral white blood cells (PWBCs). This analysis differentiated between Angus-Simmental crossbred heifers classified as fertile (n=7) and subfertile (n=5), identifying 214 DEGs involved in several pathways including immune response, metabolism, and cellular communication.
In the second study, we adopted a targeted approach by comparing the gene expression levels of known ovarian health genetic markers in the ovaries of beef heifers with differing fertility. We compared the expression of immune pathway genes, Tumor Necrosis Factor-Alpha (TNFα), and Interleukin-6 (IL6); previously identified genes, Growth Arrest And DNA Damage Inducible Gamma (GADD45G), Calcitonin-Like Receptor (CALCRL), Delta/Notch-Like Epidermal Growth Factor Repeat Containing Gene (DNER), CXC Motif Chemokine Ligand 12 (CXCL12), CCL2 (C-C Motif Ligand 2); and oocyte health genes, Epidermal Growth Factor Receptor (EGFR), Steroidogenic Acute Regulatory Protein (STAR), Zona Pellucida-Binding Protein 2 Gene (ZPBP2), Inhibin A (INHBA) in the ovaries of fertile and infertile heifers using quantitative reverse transcription polymerase chain reaction (RT-qPCR). This study was done using the same animals as the study one discussed above. There were no significant differences in transcripts targeted between fertile and subfertile heifers.
As we identified immune response as significantly altered in our first study, we next measured and compared cytokine levels in ovarian follicular fluid (FF) and blood plasma in the same groups of heifers that were used in study one and two discussed above. TNFα was significantly higher in the FF of the subfertile heifers group with no difference in the plasma, and IL6 was significantly higher in the blood plasma of fertile heifers group with no difference in the FF. IFNγ had no significant difference in the protein levels of blood plasma or follicular fluid. These findings underscore the potential of follicular fluid and plasma protein profiles as complementary biomarkers for assessing fertility in beef cattle. | en_US |
