Maintaining sperm quality during storage is essential for optimizing reproductive efficiency in rabbit breeding. This study investigated the effects of modulating calcium metabolism and the endogenous opioid system on rabbit sperm function. Two commercial extenders (TRIS and Lepus) were supplemented with calcium chloride (CaCl 2 ) and naloxone (Nx), either individually or in combination. Semen was collected from 20 New Zealand White (NZW) males, pooled, diluted, and assigned to eight experimental treatments. Sperm motility, kinematic parameters, vitality, and morphology were assessed after storage, and data were analyzed by two-way ANOVA. The results showed that treatment was the main factor affecting sperm quality parameters, whereas the effect of diluent was significant only for selected variables. The results revealed significant differences among experimental groups, with naloxone-treated samples (alone or combined with CaCl 2 ) showing the highest sperm quality. In particular, total motility (MOT) increased from approximately 56–71% in control and CaCl 2 groups to about 77–85% in Nx-treated groups, while progressive motility (PMOT) improved from approximately 44–57% to 73–82%. Similarly, kinetic parameters (e.g., VAP and VCL) were markedly enhanced in Nx and Nx + CaCl 2 groups (reaching ~60–69 μm/s and ~150–159 μm/s, respectively), whereas CaCl 2 alone consistently reduced all motility-related parameters. Sperm vitality also improved in Nx-containing treatments (up to ~0.95–0.96), compared to lower values in CaCl 2 -only groups (~0.77–0.92), while the percentage of abnormalities was reduced, particularly in TRIS-based and Nx-supplemented samples (down to ~2–4%). The combined Nx + CaCl 2 treatments consistently showed the best overall performance across most parameters. The synergistic effect observed in the Nx + CaCl 2 groups suggests that naloxone may regulate Ca 2+ influx and intracellular homeostasis, preventing detrimental effects associated with calcium overload. In conclusion, pharmacological modulation of the opioid system, particularly through low concentrations of naloxone, significantly improves rabbit semen quality and, when combined with Ca 2+ , further enhances sperm functional parameters. These findings provide new perspectives for optimizing artificial insemination (AI) protocols in rabbit production systems.
Zappone et al. (Thu,) studied this question.