Physical contact with male influences uterovaginal junction and sperm storage tubule development in Japanese quail ( <i>Coturnix japonica</i> ) at the onset of the laying cycle

The sperm storage tubules (SSTs) in the uterovaginal junction (UVJ) of female birds enable long-term sperm storage and are essential for fertility. This study examined how a two-week exposure to a fertile male affects SST morphometry, the incidence of PCNA+ cells (proliferating), and the expression of matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) in the UVJ of Japanese quail hens. At the beginning of experiment, 8 females with no prior physical or visual contact with a fertile male were selected, along with 8 hens exposed to a fertile male for 14 days. All hens were 42 days old at the beginning of experiment and has begun laying. At 56 days of age, hens from both groups were sacrificed and the UVJ was collected for morphometric, immunohistochemical and gene expression analyses. The results showed that the hens exposed to the male had significantly higher numbers, length and width of SSTs (p < 0.05). The luminal epithelium was thicker, and uterovaginal folds were longer in this group (p < 0.05). PCNA immunostaining revealed a higher incidence of proliferating cells in male-exposed hens (p < 0.05), indicating increased cellular activity within SSTs. Although MMP2 and MMP9 mRNA expression did not differ between groups, immunofluorescence revealed a stronger protein signals in hens exposed to males. The presence of males and mating significantly influences the development of SSTs in quail hens at the beginning of the laying cycle, which can promote a higher capacity for sperm storage.