02854naa a2200289 a 450000100080000000500110000800800410001902200140006002400290007410000150010324500940011826000090021250002910022152016960051265000130220865300300222165300210225165300240227265300420229670000190233870000160235770000160237370000190238970000170240870000170242577301220244210634392022-12-02       2022    bl uuuu     u00u1 u    #d  a2633-83867 a10.1530/RAF-21-01002DOI1 aHYDE, K.A.  aPreantral follicle population and distribution in the horse ovary.h[electronic resource]  c2022  aArticle history: Received in final form 25 March 2022; Accepted 4 April 2022; Accepted Manuscript published online 4 April 2022. -- Corresponding author: Gastal, E.L.; School of Agricultural Sciences, Southern Illinois University, Carbondale, IL, United States; email:egastal@siu.edu --  aAbstract: Characterization of the ovarian preantral follicle population is a necessary step to improve understanding of folliculogenesis and ovarian physiology. Therefore, in the present study, the preantral follicle population in the equine ovary in young and old mares was investigated according to follicular morphology, follicular class, distance from the geometric center using ovarian maps, and follicular density within ovarian portions (lateral vs intermediary) and regions (dorsal vs ventral). Ovaries were collected from an abattoir and histologically processed for evaluation, and the follicle population was calculated. Overall, in the current detailed study, a higher preantral follicle population per mare ovary (mean: 82,206 ± 50,022; range: 1477 to 773,091) than originally reported was identified. Additionally, a mare age effect was observed in the follicle population (young: 152,664 vs old: 11,750) and the spatial distribution of morphologically normal and abnormal follicles and the density and population of follicular classes. These results demonstrate that, in addition to the preantral follicle population in the mare ovary being comparable to that of other species, the location and spatial distribution of these follicles is dynamic and varies depending on mare age and follicle status (i.e. morphology and developmental stage). The characterization of the distribution and population of preantral follicles in the mare ovary provided by this study can potentially aid in improving reproductive studies and assisted reproductive techniques and may expand the understanding of mechanisms involving ovarian plasticity and follicular migration. © 2022 The authors.  aCABALLOS  aEquine ovarian plasticity  aFolliculogenesis  aPreantral follicles  aSpatial distribution and population??1 aAGUIAR, F.L.N.1 aALVES, B.G.1 aALVES, K.A.1 aGASTAL, G.D.A.1 aGASTAL, M.O.1 aGASTAL, E.L.  tReproduction & Fertility, 2022, Volume 3, Issue 2, Page 90-102. OPEN ACCESS. doi: https://doi.org/10.1530/RAF-21-0100