Assessment of testicular echotexture in young boars and its correlation with future semen production

Computer-assisted image analysis of testicular ultrasonography (US) can be used to assess testicular structure by objectively quantifying the brightness of pixels from US images [testicular echotexture]. In this study, testicular echotexture was assessed using B-mode testicular US in boars (n = 110) at 22, 24 and 26 weeks of age to obtain the echotexture traits such as: DKL (number of grey pixels) and Tubular Density [TUD, density of hypoechogenic areas, that is, seminiferous tubules (μm/cm²)]. Ejaculates (n = 2,498) were analysed for total number of sperm cells (TC, billion), motility and progressive motility 0 h (M0h, PM0h, %), and normal morphology (NM, %). LS means for US and semen traits were calculated per boar (Proc GLM, SAS), corrected for boar nested in line, weight (kg), age (weeks), and test month nested in season. Pearson's correlation (Proc Corr, SAS) was used to assess the correlation between boar's LS means (Least Square means) for US and semen traits. DKL was not significantly (p > 0.05) different in boars at 22 (158.1 ± 0.8), 24 (159.0 ± 0.7) and 26 weeks of age (158.9 ± 0.8), but TUD decreased (p < 0.05) from 22 weeks (106.0 ± 1.3) to 24 or 26 weeks (98.4 ± 1.0 and 98.1 ± 1.1 μm/cm²), showing an increase in testicular echogenicity with age, which happens during sexual development. DKL had a negative correlation (p < 0.05) with the TC (R = -0.54), M0h (R = -0.19), PM0h (R = -0.42), and NM (R = -0.40). TUD had a positive correlation (p < 0.05) with TC (R = 0.51) and with NM (R = 0.32). Thus, boars with higher tubular density produced a higher number of sperm cells with fewer morphological abnormalities, while boars with a higher number of grey pixels showed the opposite. Since DKL can be measured at 22 weeks of age, it could be the trait of choice for early selection of boars for productivity. This early selection could reduce the costs of semen production. Further research is needed to define the genetic basis of these traits, assess their relevance for breeding programs, and evaluate whether echotexture parameters can serve as objective markers of puberty onset in boars.