A brief histological profile of the ovary of the hog badger (Arctonyx collaris)

Introduction

The Greater Hog badger (Arctonyx collaris) is a large, terrestrial carnivorous mammal belonging to Mustelidae with robust forelimbs, enlarged distinct white claws, a tail with long white hairs, and distinct, generally omnivorous in feeding. In 2008, three subspecies of hog badgers were recognized, namely the Greater, Indonesian, and Burmese hog badgers. The animal possesses medium length fur (white to brown), white throat, elongated pig like snout pink colored and compact body (Helgen et al., 2008) [4] . This species is mostly found in the eastern Himalayan region, including northeastern India, Thailand, Assam, and Myanmar (Wozencraft, 2005) [8] . A major conservation concern is the rapid decline in hog badger populations, primarily due to poaching and anthropogenic pressures (Duckworth et al., 2016; Baker, 2012) [2,1] . Adult individuals typically measure 65-104 cm in body length, with a tail length of 19-29 cm and a body weight ranging from 7-14 kg (Helgen et al., 2008) [4] . Females attain early sexual maturity (2-3 month), whereas males, around one year of age. Independence timing has been documented in American badgers (Edmunds, 2003) [3] . Hog badgers exhibit relatively low levels of physical activity and active during both day and night (Helgen et al., 2008) [4] . Successful reproduction and offspring survival are critical for the long-term sustainability of the species; however, limited information is available regarding the structural organization of the reproductive system, particularly in hog badgers. Ovarian histomorphology is an important indicator of reproductive efficiency (Souza et al., 2005; Silva et al., 2006) [6,5] . In order to establish baseline anatomical and histological data on the ovary of the hog badger (Arctonyx collaris), the present study was undertaken to examine the morphological profile of reproductive tissues obtained during post-mortem examinations conducted at Sepahijala Zoo, Tripura.

Materials and Methods

Necropsy of the sub-adult female Hog Badger was performed at College of Veterinary Sciences and Animal Husbandry, R.K. Nagar, Tripura from the Sepahijala Zoo, Tripura, India. On necropsy, the animal was found to have died due to acute gastroenteritis. During the necropsy, the female genital system was found to be normal. The whole ovary was separated from the surrounding fascia and 3-4 mm ovarian tissue was collected and kept in 10% neutral buffered formalin for 72 hr for fixation for histological studies followed by standard tissue processing procedures (Suvarna et al., 2019) [7] . 5 µ thick tissue sections were obtained using a semi-automatic rotary microtome and stained with haematoxylin and eosin, Massons-Tri-chrome for collagen fibers (Suvarna et al., 2019) [7] . Micro-metrical observations for size of different follicles (primordial, primary, secondary and mature), germinal epithelium profile, thickness of thecal layer, germinal epithelium, zona pelucida, antral diameter, size of luteal granulosa cell, thickness of corona radiata, nucleus diameter etc breadth were recorded randomly at least in ten fields. Photography and measurements were performed using Zeiss Trinocular Microscope with an attached computer installed with Zen.3.11 micrometry software.

Results and Discussion

Microscopic Architecture

Microscopically, the ovary was composed outer cortex and inner medulla. The cortex was characterized by ovarian follicles of different generations, and medulla contained blood vessels, connective tissue, lymphatics, and nerves. Ovary was covered by a tall cuboidal to columnar single layer germinal epithelium, with a mean height of 4.86±0.17 µm. Beneath this surface epithelium, a thin distinct tunica albuginea clearly separated the epithelium from the underlying cortex. The ovarian cortex appeared darkly stained and consisted of ovarian follicles at various stages of development within a stromal connective tissue matrix. In contrast, the medulla was lightly stained and with loose connective tissue. Irregularly branched trabecular connective tissue extended from the medulla toward the cortex. Histological sections revealed follicles ranging from primordial to tertiary stages. Primordial follicles measured 10±1 µm in diameter, primary follicles averaged 50±3 µm, secondary follicles measured 104±7.57 µm, and only a few tertiary follicles were observed, with an average diameter of 180±4.2 µm. Primordial follicles, were surrounded by an incomplete single layer of flattened squamous cells with whorled arrangement of connective tissue fibers and cells. Primordial and primary follicles were predominantly distributed in the peripheral subgerminal region beneath the germinal epithelium. Primary follicles were larger and consisted of a single layer of cuboidal follicular (granulosa) cells surrounding an oocyte with a large, round nucleus. Secondary follicles were single layered to multilayered granulosa cells, with indistinct thecal layer. Tertiary follicles were characterized by antrum, and granulosa cells. The granulosa cells were characterized by large, round, euchromatic nuclei, indistinct cellular boundaries, and cloudy cytoplasm. Secretory activity and the irregular outlines of these cells produced a flare-like appearance extending toward the zona pellucida. Large lipid droplets were observed within the antral cavity. The primary oocytes within tertiary follicles were predominantly eccentrically positioned, although centrally located oocytes were observed. A thin layer of granulosa cells forming the cumulus oophorus surrounding the oocytes.

Key Microscopic observations noted

Discussion

This histomorphological study propose the first description of ovarian structure in the hog-badger (Arctonyx spp.) and provides morphological evidence of actively cycling normal ovary. The basic organization of the ovary, with follicle-rich cortex and a highly vascularized medulla, is consistent with the ovarian anatomy described in other mammals and closely related carnivores such as mustelids, canids, and felids, as well as in several wild ungulate species. Ovarian follicles representing different stages of development, primordial (10±1 µm) to tertiary follicles (180±4.2 µm), were identified, evident of ongoing folliculogenesis. The high proportion of primordial and primary follicles located in the sub germinal zone and it may be acting as reserve follicular pattern observed across mammalian species (Souza et al., 2005; Silva et al., 2006) [6,5] . In contrast, relatively low number of tertiary follicles were observed. Which may be suggesting that the ovary was examined during an inter-ovulatory period. Well-defined distinct zona pellucida (2±0.05 µm) and corona radiata (14. [3,4] suggest comparatively early reproductive competence relative to other mustelids. Few atretic follicles were observed in the present study, degenerating pyknotic granulosa cells and oocytes, suggestive of normal follicular atresia. The well-established connective tissue network within the medulla (Suvarna et al., 2019) [7] highlights the ovarian considerable metabolic demands for steroidogenesis and follicular growth. For Arctonyx species, these baseline histological findings collectively establish fundamental reproductive parameters (Duckworth et al., 2016; Baker, 2012) [2,1] . As per Wozencraft (2005) [8] and Helgen et al. (2008) [4] , the species' wide range in the eastern Himalayan region, northeastern India, Thailand, Assam, and Myanmar coincides with regions that are experiencing severe habitat fragmentation. For exclusive understanding of breeding cylicity, reproductive senescence, and morphophysiological relationships, future research is required, with larger sample sizes considering the seasons.

Conclusion

This study aimed to draw baseline information on ovarian microanatomical studies for this vulnerable species through. Typical mammalian ovarian organisation and active reproductive cyclicity are confirmed by the presence of follicles at all developmental stages, active and regressing corpora lutea, and a well-vascularized medullary stroma.

For upcoming comparative and conservation-focused studies, quantitative morphometric measurements provide useful benchmarks.

Acknowledgement

AcknowledgementsAuthors extend their sincere thanks to Principal, College of Veterinary Science and Animal Husbandry, R.K. Nagar, Tripura, India for providing all the facilities. Authors are also extending sincere thanks to the Sepahijala Zoo authority.

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