Abstract
Background:
Dwarf hamsters are extensively used as models in reproductive disorders studies, reproductive endocrinology, embryo transplantation, and in vivo and in vitro egg fertilization.

Aim:
This study aimed to explore the morphological and morphometric development of the ovary with T lymphocyte distribution at different ages using immunohistochemical cluster of differentiation 40 (CD40) expression.

Methods:
Fifteen dwarf hamster (Phodopus roborovski) females were used in this study and divided into three groups at three different ages (2, 4, and 8 weeks) after birth. Samples were collected, and the length, width, and weight were measured. Standard histological processing was performed, and the slides were stained with hematoxylin and eosin. Histomorphometrical analysis was performed using a 3.0 USB microscopic camera for determining the numbers and diameters of the primordial, primary, secondary, and Graafian follicles and the diameter of the mature oocyte and corpus luteum. Immunohistochemical analysis using CD40 anti-Mouse ligand antibody expression to evaluate T lymphocyte distribution within ovarian parenchyma.

Results:
At 2 weeks of age, the observations showed symmetric development of the ovaries, with no significant differences in dimensions and weight. Histologically, the ovaries displayed early follicle development with sparse T lymphocytes. At 4 weeks, follicular size asymmetry emerged with the presence of corpus luteum and increased T lymphocyte counts. By 8 weeks, the ovaries exhibited more developed ovarian follicles, larger corpus luteum, and a further increase in T-lymphocyte density.

Conclusion:
This investigation sheds light on the development of the ovary in dwarf hamsters, an understudied model with a short maturity age. These findings provide a promising understanding of ovarian morphological development and the diagnosis of various infertility developmental disorders.

Key words: Keywords: Dwarf hamster, Development, Ovary, Ovarian follicles, T-lymphocytes