Breed-specific testicular ultrasound profiles and pubertal markers in Bos indicus and composite bulls

Ultrasonography has offered potential to detect breed-specific differences and identify early puberty biomarkers in bulls. This study aimed to (a) characterize testicular ultrasound parameters in young bulls of the Nelore (Bos indicus) and Canchim (composite: 5/8 Bos taurus × 3/8 Bos indicus) breeds, and (b) identify potential ultrasonographic biomarkers associated with the pre- and post-pubertal phases. A total of 46 young (Nelore, n = 22; Canchim, n = 24) were evaluated using testicular biometry, B-mode ultrasonography, color Doppler of the parenchyma and pampiniform plexus, and spectral Doppler of the supratesticular artery. Semen analysis and serum testosterone measurements were conducted to determine pubertal status. Monthly collections were performed with longitudinal monitoring from 8 to 19 months of age. Subsequently, the animals were grouped into pre-pubertal and post-pubertal cohorts. Statistical analyses were performed using PROC MIXED in SAS, with significance set at P < 0.05. Significant temporal increases were observed in scrotal circumference (P < 0.001), testicular volume (P = 0.03), parenchymal echogenicity (P = 0.0007), and relative Doppler area (P = 0.0003). At most timepoints, Canchim bulls demonstrated consistently higher values than Nelore bulls. Notably, pre-pubertal Canchim bulls exhibited greater testicular echogenicity compared to their post-pubertal counterparts (P = 0.03), while pre-pubertal Nelore bulls showed reduced Doppler perfusion in the testicular parenchyma relative to post-pubertal individuals (P = 0.03). This study highlights significant breed-related differences in testicular ultrasound parameters during sexual maturation. Canchim bulls exhibited higher echogenicity and testicular perfusion compared to Nelore bulls. Furthermore, ultrasonographic features such as echogenicity and Doppler area emerged as promising, non-invasive biomarkers for monitoring pubertal development in beef cattle.