Testicular Echobiometry and Sperm Characterization in Oncilla (Leopardus tigrinus) From the Caatinga Biome

Among neotropical small felids, the Leopardus tigrinus is classified as vulnerable by the International Union for Conservation of Nature, but studies on reproductive morphology and physiology are scarce for conservation strategies. This study aimed to describe testicular biometry and sperm characteristics of L. tigrinus from Ceará, Brazil, in the Caatinga biome. Four animals (≥ 2.3 ± 0.3 years old; 2.5 ± 0.2 kilograms) were chemically restrained with a combination of dexmedetomidine and ketamine. Testicular parenchyma was assessed by ultrasonography, with volumes calculated using Lambert and ellipsoid formulas. Semen was collected by electroejaculation, and macroscopic (volume, color) and microscopic parameters (concentration, motility, viability, hypoosmotic swelling test) were evaluated. Morphology and morphometry were described, and samples were processed for scanning electron microscopy. Statistical analysis was performed using GraphPad Prism software. Results showed that testicular volume calculated by the Lambert and ellipsoid formulas was 3.11 ± 0.21 cm³ and 2.29 ± 0.16 cm³, respectively. Ejaculates had 237.5 ± 89.9 µL volume, 1.4 ± 0.7 × 10⁹ sperm/mL concentration, 55.0 ± 15.4% motility, 3.5 ± 0.3 vigor, 51.8 ± 16.8% viability, 75.0 ± 8.6% hypoosmotic response, and 60.8 ± 10.2% morphologically normal spermatozoa. Morphometric analysis described a total length of 29.50 ± 0.10 µm. Ultrastructural evaluation allowed a more detailed description of the sperm morphology, defining the sperm head of oncillas as oval-shaped, the sperm neck, and the acrosomal regions (equatorial and apical segments). Thus, this study advances knowledge on L. tigrinus reproductive morphophysiology, emphasizing the application of testicular ultrasonography in the species and providing crucial data on sperm characteristics for implementation of reproductive biotechnologies as a conservation strategy.