Optimization of Glycerol Concentration and Freezing Rate in the Cryopreservation of Ejaculate From Brown Bear (Ursus arctos)

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ContentsIn order to establish a semen bank for the endangered Cantabrian brown bear, we tested five glycerol concentrations and three freezing rates for electroejaculated semen. Electroejaculation was performed on nine males. Semen was diluted in TES–Tris–Fructose (20% egg yolk, 2% EDTA, 1% Equex) with 2%, 4%, 6%, 8% or 10% glycerol and frozen at −10, −20 or −40°C/min. Before and after cryopreservation, samples were analysed for motility (CASA), viability and acrosomal status (flow cytometry). Pre-freezing results showed that glycerol concentration had no significant effect on total motility or progressive motility, but it significantly decreased VCL, ALH, viability and acrosomal status (p < 0.05). After thawing, sperm motility was higher at extender with 4%, 6% and 8% glycerol, but only at 4% and 6% glycerol for viability and acrosomal status. For 4% and 6% glycerol, freezing rates did not have significant effects. The curve fitting gave an estimate of the optimal glycerol concentration, with all the optimal values for every parameter between 6% and 7% glycerol falling. We propose using 6% glycerol and a freezing velocity of −20°C/min for freezing brown bear ejaculated spermatozoa.

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