Evaluating ovarian follicles and their steroid hormone gene expression patterns in a high egg-producing research turkey line

Authors: HALL, GEORGE - US Department Of Agriculture (USDA); Hildenberger, Diane; Long, Julie; Diehl, Kristen

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2024
Publication Date: 11/26/2024
Citation: Hall, G.B., Hildenberger, D.M., Long, J.A., Diehl, K.M. 2024. Evaluating ovarian follicles and their steroid hormone gene expression patterns in a high egg-producing research turkey line. Poultry Science. 104(1). Article e104592. https://doi.org/10.1016/j.psj.2024.104592.
DOI: https://doi.org/10.1016/j.psj.2024.104592

Interpretive Summary: Turkey hens that lay only a few eggs per week impact the economic profitability of commercial operations. Low-egg producing turkey hens require the same feeding and care as high-egg producing hens but contribute fewer offspring for production. Two specialized turkey lines with different rates of egg production (high versus low) were evaluated to investigate the biological and genetic basis for the differences in egg production between the the two lines. Egg production traits, ovarian and follicle anatomical characteristics, and gene expression for reproductively important genes were measured. Ovaries and the number of preovulatory follicles were the same between the two lines; however, ovarian follicles for the high-egg producing line matured at a quicker rate, leading to a an increased clutch length. Additionally, changes in gene expression related to hormone receptors suggested differences in the steroid hormone synthesis pathways. Understanding the biological mechanics behind egg-production rates in turkeys will greatly benefit the industry.

Technical Abstract: Low egg-producing turkeys reduce the profitability of a flock by limiting the number of poults that can be hatched. Understanding the biological mechanics behind egg-production rates in turkeys will greatly benefit the industry. Two lines with vastly different egg production rates are the Ohio State University E line, which was selected for high egg production rates, and the unselected counterpart, the random-bred control one (RBC1). Differences between E Line and RBC1 hens (n = 4 per group) during a 62-day trial (28 to 37 weeks of age) were investigated by measuring egg production traits, ovarian and follicle gross anatomical characteristics, and gene expression for reproductively important genes within different follicle types. Data were analyzed with either a student’s t-test in Excel for production traits and ovarian or follicle morphology, or with ANOVA mixed model procedure in SAS for gene expression. The E line hens produced 20% more eggs than the RBC1 hens by increasing clutch length and keeping the pause length the same. The E line ovaries were similar in size compared to the RBC1 hens, along with having the same number of preovulatory follicles. The E line hens saw less LHCGR expression in small white follicles (SWF) which coincided with downregulation of CYP11A1 and CYP17A1. PRLR was upregulated in small yellow follicles (SYF) which also coincided with downregulation of CYP17A1, in both cases changes in pituitary hormone receptor transcription levels appeared to affect the steroid hormone synthesis pathway. In SWF, large white follicles, and selected follicles ESR1 or ESR2 were downregulated. The similarity in preovulatory numbers suggests that E line hens aren’t selecting more follicles to grow, but instead, follicles are growing faster. Based on the gene expression patterns the reduction of steroid hormone synthesis might hint at the follicles putting more energy into growth and differentiation. At the same time, the decrease in estradiol receptor might limit the negative effects of estradiol on follicular granulosa cells and allow for more rapid growth.