K. Kotzev, S. Sevov, G. I. Kalaydzhiev, D. Abadjieva
Institute of Biology and Immunology of Reproduction “Acad. Kiril Bratanov”, Bulgarian Academy of Sciences, blvd. 73 Tsarigradsko Shose Street, 1113, Sofia, Bulgaria
Faculty of Agriculture, Trakia University, 6000, Stara Zagora, Bulgaria
(Manuscript received 10 June 2026; accepted for publication 31 August 2026)
e-mail: krasimir.kotzev9@gmail.com
Abstract. The objective of this study was to investigate the relationship between selected biochemical markers in seminal plasma and sperm motility parameters in frozen-thawed ram semen. A total of 18 frozen semen samples from 18 adult Lacaune rams, aged 3-5 years, were analyzed. Following thawing, seminal plasma was separated for biochemical analysis, while the remaining semen was diluted 1:1 with 6A extender and evaluated using computer-assisted sperm analysis (CASA). The concentrations of alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), lactate dehydrogenase (LDH), creatine kinase (CK), calcium (Ca²⁺), and magnesium (Mg²⁺) were determined. Associations between biochemical and sperm motility parameters were evaluated using correlation analysis. A significant negative correlation was observed between LDH activity and progressive motility (r=−0.48; P≤0.05), while LDH showed a significant positive association with the immotile fraction (r=0.49; P≤0.05). The negative correlation between GGT activity and progressive motility (r=−0.42) did not reach statistical significance. CK activity showed moderate negative, but non-significant, correlations with sperm concentration (r=−0.49), and LDH activity was similarly not significantly correlated with sperm concentration (r=−0.46). Furthermore, despite a significant interrelation between Ca²⁺ and Mg²⁺ (r=0.44; P≤0.05), no statistically significant correlations were observed between the Ca/Mg ratio and the analyzed sperm motility parameters. The results demonstrate associations between selected biochemical markers, particularly LDH activity, and sperm motility parameters in post-thaw ram semen. These findings suggest that seminal plasma biochemical analysis may provide complementary information to standard CASA parameters for the evaluation of frozen–thawed ram semen. However, given the limited sample size, further studies are required to confirm the observed relationships and determine their practical relevance.