Antibiotics for the refrigerated storage at 4 °C of hormonally induced European сommon frog (Rana temporaria) spermatozoa

A valuable reproduction technology for the sustainable management of amphibian biodiversity is the refrigerated storage of spermatozoa at 4 °C. Antibiotics offer the potential to increase the storage life of refrigerated spermatozoa by inhibiting bacterial growth. In the present study, the effect of antibiotics lincomycin, enrofloxacin and gentamicin, alone or in combination, on the retention of motility, and longevity of spermatozoa in the spermic urine of the European common frog (Rana temporaria) during a 36-day storing period in the refrigerator at 4 °C was investigated. The percentage of motile spermatozoa declined in each treatment group over time; however, in samples supplemented with three antibiotics in combination or gentamicin alone, the sperm motility was significantly higher (from 17 % to 52 %) on Day 30 after sperm collection than that in samples in control and other antibacterial groups. Lincomycin did not improve the spermatozoa longevity during refrigerated storage, and enrofloxacin had a less pronounced beneficial effect than gentamicin did. Also, the effect of gentamicin at concentrations of 15, 30, 60, 100, 200, 400 µg/mL, and 1, 2, 4 mg/mL for maintaining sperm motility during refrigerated storage was evaluated. Gentamicin at concentrations of 30–400 µg/mL had a positive effect on the retention of sperm motility, with the highest rates of motility during storage at a concentration of 100 µg/mL. Gentamicin at a concentration of 15 µg/mL had no effect on maintaining sperm motility. The sperm motility was partially inhibited by gentamicin at concentrations of above 400 µg/mL (1 and 2 mg/mL) and stopped completely at 4 mg/mL. Moreover, gentamicin effects on the cleavage of fertilized eggs and subsequently on the hatch rates were evaluated. Аfter 30 days of refrigerated storage with 30–120 μg/mL gentamicin, the motility of the spermatozoa in more than half of the samples was 50 % and above. The cleavage rate of eggs (55.0 ± 5.9 %) and the hatching rate of cleaved eggs (68.2 ± 2.9 %) did not differ significantly from those obtained for fresh spermatozoa (P