Comparison of morphological and morphometric characteristics between follicles with one or more oocytes in sheep ovaries

The investigation of morphological characteristics of the population of preantral follicles is important for the understanding of physiological processes such as folliculogenesis and for new reproductive strategies. The aim of this study was to morphologically characterize the population of sheep ovarian follicular reserve. Ovine ovaries (n = 32) were histologically processed and analyzed by light microscopy. The follicles and oocytes showed the following average diameters: (primordial with one oocyte) 30.96 ± 4.6 m and 25.09 ± 1.61 mm; (multioocyte primordial) 48.62 ± 5.66 m and 24.31 ± 3.35 mm; (primary) 50.96 ± 8.52 m and 34.42 ± 4.50 mm; (secondary) 86.48 ± 21.85 m and 49.01 ± 11.49 mm; (antral) 226.26 ± 69.93 m and 66.26 ± 11.01 micrometers. Data were compared were using the Wilcoxon test for dependent samples. There was no difference between oocyte diameter in primordial follicles with one or more oocytes. Multioocyte follicles at the primordial stage were observed in greater amounts than secondary follicles, and their prevalence was similar in the right and left ovaries (p = 0.792). Regarding the macroscopic analysis, data were subjected to Spearman correlation test. There was a positive correlation between follicular population and ovarian diameter (p < 0.01), ovarian weight (p < 0.05) and ovarian volume (p < 0.05). The was not correlated with the other variables. However, correlation of total number of multioocyte follicles with follicular average population approached significance (p = 0.056). These results suggest that multioocyte primordial follicles have morphology and developmental capacity similar to primordial follicles with one oocyte.