Abstract

Background:
Prenatal ovarian development is a critical process that determines future reproductive capacity, yet detailed morphological and histological data in sheep fetuses remain limited.

Aim:
This study aimed to investigate the prenatal morphological and histological development of sheep ovaries at different gestational stages.

Methods:
Ten fetuses were obtained from healthy pregnant ewes and classified into two gestational groups based on crown–rump length: Group I (90–100 days) and Group II (140–145 days). Gross anatomical observations were performed, followed by histological examination of ovarian tissues.

Results:
In Group I, the ovaries were small and elongated, with asymmetry in shape, as the left ovary appeared pearshaped while the right was more uniformly elongated. Both ovaries were translucent, whitish, and located caudal to the metanephros within the abdominal cavity. Histologically, the ovaries consisted of distinguishable cortical and medullary regions based on the distribution of germ cells and undifferentiated mesenchymal cells. In Group II, the ovaries were larger, elongated, and more clearly defined, exhibiting a translucent whitish to creamy appearance. Microscopically, a well-developed cortex and medulla were evident, with a distinct tunica albuginea, clearly defined germinal epithelium, and a densely cellular cortex containing primordial, primary, and secondary follicles.

Conclusion:
Fetal sheep ovaries exhibit marked morphological and histological maturation from the second to the third trimester, with major ovarian differentiation and early folliculogenesis occurring predominantly during late gestation, thereby establishing the structural foundation for postnatal reproductive function.

Key words: Development; Fetuses; Ovary; Prenatal; Sheep.