Telomere lengths in blood and sperm as biomarkers of reproductive aging and semen quality in dogs.

To assess the potential utility of leukocytes and spermatozoa telomere length (LTL and STL) as reproductive biomarkers, this study measured both LTL and STL and investigated their possible correlations with oxidative status and semen quality parameters in healthy breeding male dogs. Twenty-two ejaculates and blood samples were collected from dogs of various breeds. Semen was evaluated for volume, concentration, sperm motility, and kinetic parameters using a Sperm Class Analyzer. LTL and STL were quantified using Quantitative PCR (qPCR) and expressed as the relative ratio of telomere repeat copy number (T) to a single-copy gene (S), T/S ratio. Serum oxidative stress markers were assessed using d-ROMs and Biological Antioxidant Potential (BAP) tests. Correlations between STL and LTL, as well as their association with age, semen parameters and oxidative stress levels, were evaluated using Spearman analysis. LTL and STL were 0.63 ± 0.25 and 0.85 ± 0.31 and showed a strong positive correlation (P < 0.001; r s =0.70). Both LTL and STL were also negatively correlated with age (P < 0.05 and rs = 0.50; P < 0.001 and rs = 0.68). The cut-off age for the difference in STL and LTL was identified at 6 and 7.5 years, respectively. STL was also positively correlated with semen volume (P < 0.05; r s concentration (P < 0.05; r s = 0.63) and =0.41) and negatively correlated with semen chromatin decondensation (P < 0.01; r s =-0.71); while the LTL showed a positive correlation with sperm concentration (P < 0.05; r = 0.53). No correlations with oxidative markers were found. These findings support the potential use of TL as a biomarker for reproductive aging and semen quality in dogs.