Diagnostic agreement between ovarian ultrasonography and vaginal cytology for estrous cycle phase identification in bitches.

This observational cross-sectional study evaluated the agreement between transabdominal ovarian ultrasonography and vaginal cytology for estrous cycle phase identification in bitches under routine university clinical conditions. Fifty intact, client-owned bitches of different breeds, body sizes, and ages presented to the Veterinary Teaching Clinic of the Pontifícia Universidade Católica do Paraná (CVE-PUCPR) were included. Each animal underwent B-mode and color Doppler ultrasonography of the ovaries and uterus, followed by vaginal smear collection using a sterile speculum-assisted technique. Cytological smears were stained using a rapid Romanowsky-type stain, the rapid Panoptic method, and interpreted by an evaluator blinded to the ultrasonographic classification. Estrous cycle phases were classified independently by each method as anestrus, proestrus, estrus, or diestrus using predefined morphological and cytological criteria. Ultrasonography classified 22%, 34%, 4%, and 40% of bitches as anestrus, proestrus, estrus, and diestrus, respectively, whereas vaginal cytology classified 34%, 20%, 14%, and 32% in the same phases. Strict four-phase agreement was 50.0% (25/50; 95% CI, 36.6-63.4), with unweighted Cohen's kappa indicating fair agreement beyond chance (κ = 0.31; 95% CI, 0.13-0.49; P = 0.0002). When ultrasonographic proestrus paired with cytological late proestrus/estrus was interpreted as a clinically contiguous periovulatory classification, adjusted periovulatory clinical concordance increased to 64.0% (32/50; 95% CI, 50.1-75.9). Spearman's rank correlation was retained only as an ordinal association measure and not as evidence of diagnostic agreement. Because progesterone or luteinizing hormone assays were not performed, this study does not validate either method against an endocrine reference standard. Instead, the findings indicate partial, phase-dependent agreement and clinical complementarity between ovarian ultrasonography and vaginal cytology for estrous cycle assessment in bitches.