Developmental and histochemical study of the reproductive system in female dogs during the postnatal period, Розвиток та гістохімічне дослідження репродуктивної системи самок собак у постнатальний період

<jats:p>The early postnatal organogenesis of the canine female reproductive tract marks a critical phase of morphofunctional and histochemical remodeling. This study targeted the biological characterization of age-dependent tissue development in the ovaries, uterus, and oviducts of female canine puppies between the 3rd and 8th weeks of postnatal life. Experimental procedures were executed using healthy female puppies divided into two age-matched cohorts (n=3). Excised tissue samples were fixed in 10 % neutral buffered formalin, embedded in paraffin, sectioned at 4–7 μm, and subjected to hematoxylin-eosin, Alcian blue (pH 2.5), and Periodic acid–Schiff (PAS) staining. Morphometric processing was performed using the Fiji ImageJ software, and mean differences were statistically evaluated via the independent samples Student t-test using SPSS. Histochemical evaluation confirmed the physiological initiation of endometrial secretory activity, as marked by the transition of neutral mucopolysaccharides within the uterine glands from a completely negative profile at 3 weeks to a distinct weak positive reaction by the 8th week of age. Morphometrically, the uterine wall exhibited highly significant vertical cellular hypertrophy of the luminal lining, manifested by a 5.2-fold increase in epithelial height from 5.50±0.93 μm to 28.50±2.91 μm (P=0.0001). Concurrently, intense longitudinal organ elongation resulted in a significant 39.4 % reduction in total uterine wall thickness from 447.40±53.45 μm to 271.30±40.45 μm (P=0.0303) and a synchronized 39.3% reduction in total oviductal wall thickness from 220.00±29.74 μm to 133.50±4.71 μm (P=0.0207). While the primary inner oviductal luminal epithelium maintained strict cytological stability between the 3rd and 8th weeks (10.00±1.76 μm versus 11.90±1.53 μm, respectively; P=0.4407), the functional ovarian cortex exhibited active folliculogenesis, characterized by a statistically significant 23.6 % linear expansion of the primordial follicle diameter from 27.50±1.20 μm to 34.00±1.85 μm (P&lt;0.05). These quantitative relative and absolute indices establish definitive baseline criteria for mammalian reproductive histogenesis and provide critical reference profiles for evaluating developmental pathology in canine veterinary medicine.</jats:p>