Variation in antral follicle number but not primordial follicle number is positively related to luteal function in beef heifers

Authors: Cushman, Robert - Bob; BEDKE, CLAYTON - University Of Wyoming; SHULTS, MADISON - University Of Wyoming; QUAIL, LACEY - Texas A&M University; EPPERSON, KAITLIN - Texas A&M University; Snider, Alexandria - Alex; PERRY, GEORGE - Texas A&M University; SCHOLLJEGERDES, ERIC - New Mexico State University; SUMMERS, ADAM - New Mexico State University; LAKE, SCOTT - University Of Wyoming; CUNNINGHAM-HOLLINGER, HANNAH - University Of Wyoming; ROSASCO, SHELBY - University Of Wyoming

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/29/2022
Publication Date: 7/18/2022
Citation: Cushman, R.A., Bedke, C.D., Shults, M.A., Quail, L.K., Epperson, K.M., Snider, A.P., Perry, G.A., Scholljegerdes, E.J., Summers, A.F., Lake, S.L., Cunningham-Hollinger, H.C., Rosasco, S.L. 2022. Variation in antral follicle number but not primordial follicle number is positively related to luteal function in beef heifers [abstract]. Society for the Study of Reproduction Annual Meeting, July 26-29, 2022, Spokane, Washington. Poster P120.

Interpretive Summary:

Technical Abstract: The relationship between antral follicle number and ovarian steroid production in cattle remains controversial. Most studies report increased circulating luteal phase progesterone concentrations in bovine females with greater numbers of antral follicles, but some studies report that greater numbers of antral follicles are associated with decreased circulating progesterone concentrations. There is an antagonistic genomic relationship between antral follicle count and age at puberty, indicating that females with very high numbers of follicles have delayed puberty. Together, these data imply that antral follicle number influences endocrine function before and after puberty and may impact ovarian steroid production during the bovine estrous cycle. Issues with these methods that could lead to discrepancies in results include the possibility of technician error when ultrasonography is used to determine antral follicle number and the use of classes for a continuous trait like antral follicle count, because different investigators place the thresholds at different levels, which can dramatically change the results. To further investigate the relationship between follicle numbers and luteal function we collected ovaries at day 16 of an induced estrous cycle in pubertal Angus heifers and used surface counts as a gold standard to understand luteal function. Based on past results from our laboratory, we hypothesized that antral follicle number would be positively associated with progesterone concentrations and luteal weight at day 16 of the estrous cycle. Angus heifers (n = 72) were synchronized using the CO-Synch protocol and ovaries were recovered on day 16 after the second GnRH injection, either at slaughter or by flank laparotomy. A blood sample was collected on day 16 immediately prior to recovery of the ovaries for determination of circulating progesterone concentrations by radioimmunoassay. Upon recovery of the ovaries, all surface follicles were counted, the corpus luteum was dissected from the ovary and weighed, and a representative piece of ovary was fixed for histological evaluation of primordial follicle number. Regression analysis was applied using the REG procedure of SAS to determine the direction and magnitude of the relationship between antral follicle number, primordial follicle number, weight of the corpus luteum, and progesterone concentration. Antral follicle number was positively related to weight of the corpus luteum (r-square = 0.05; P = 0.03) and progesterone concentration (r-square = 0.05; P = 0.05). Primordial follicle number was positively related to antral follicle number (r-square = 0.32; P < 0.0001), but not to weight of the corpus luteum or progesterone concentration (P > 0.39). We conclude that there is a positive relationship between antral follicle number and luteal function in pubertal beef heifers. The fact that this relationship does not exist with primordial follicles implies that gonadotropic support and steroidogenic feedback from the pool of small antral follicles drive this difference in luteal function and should be further investigated in heifers with increased numbers of antral follicles to understand how it influences attainment of puberty and control of regular estrous cycles. USDA is an equal opportunity provider and employer.