Integrated ultrasonographic, endocrine, seminal, and morphological characterization of cryptorchidism in collared peccary (Pecari tajacu).

Cryptorchidism is a congenital reproductive disorder that can compromise fertility and represents a challenge for conservation and management programs in wildlife species. In collared peccary (Pecari tajacu), reports of this condition are rare and generally limited to imaging findings. This study reports a case of unilateral cryptorchidism in an adult male collared peccary, providing an integrated ultrasonographic, biometric, endocrine, seminal, and morphological characterization. Clinical examination revealed the absence of the left testis in the scrotum, with an inguinal mass suggestive of testicular retention, which was confirmed by ultrasonography. Ultrasonographic evaluation demonstrated a retained testis with reduced size and homogeneous hypoechoic echotexture, whereas the scrotal testis showed increased volume and discrete echotextural alterations. Testicular biometry revealed marked asymmetry between the testes, with reduced length, width, thickness, and volume of the cryptorchid testis compared with the contralateral scrotal testis, which exhibited hypertrophy. Serum testosterone concentration was markedly elevated (15,940 pg/mL), exceeding reference values for the species. Seminal analysis revealed reduced sperm concentration (380 × 106 spermatozoa/mL) compared to healthy individuals, although motility (74%) and sperm morphology (69% normal cells) remained within ranges compatible with fertility. Reduced mitochondrial activity and plasma membrane functionality suggested potential limitations in functional fertility. Histological evaluation demonstrated preserved architecture and complete spermatogenesis in the scrotal testis, whereas the retained testis exhibited tubular atrophy and absence of advanced stages of spermatogenesis. Despite methodological considerations regarding hormonal assessment, the findings support a compensatory hypertrophic and endocrine response of the scrotal testis in unilateral cryptorchidism. This case expands current knowledge on reproductive pathology in collared peccary and highlights the importance of integrated diagnostic approaches for reproductive health assessment and management in captive wildlife populations.