Spatial differences in the ovine cervical microenvironment at the follicular and luteal phases of the oestrous cycle; Implications for sperm transport

The complex anatomy of the ovine cervix presents a significant barrier to transcervical artificial insemination, necessitating sperm deposition at the external cervical Os. This study aimed to evaluate the cervical microarchitecture to elucidate the mechanisms orchestrating sperm transport across the cervix. Cervices from crossbred ewes (n = 13) were harvested during the follicular (n = 6) and luteal (n = 7) phase, sectioned into 10 transverse segments from external to internal Os (1 = External cervical Os; 10 = Internal cervical Os), and analysed for epithelial morphology and microgroove architecture. Columnar epithelium predominated throughout the cervix, with a squamocolumnar junction localised at the external Os. Columnar cell height was significantly greater during the follicular phase (33.3 ± 1.31 μm) than the luteal phase (26.7 ± 1.21 μm; p < 0.001). Cervical microgroove surface area increased during the follicular phase (p < 0.05). Microgroove surface area, depth, and tortuosity (deviation from a straight line) increased progressively toward the internal Os and were enhanced during the follicular phase (p < 0.05). Sialic acid expression was elevated in secondary and tertiary microgrooves during the follicular phase (p < 0.001), with mucin-bound sialic acids showing spatial variation along the canal. Segment 4 exhibited the lowest sialic acid expression (p < 0.01). Reproductive phase by cervical segment interactions affected both the secondary, tertiary microgroove epithelium, and surrounding luminal region adjacent to the tertiary microgrooves (p < 0.001). This study provides a detailed characterisation of the microarchitecture of the ovine cervical canal which is critical to understanding the mechanisms orchestrating sperm transport.