In vitro evaluation of in vivo fertilizing ability of frozen rabbit semen
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The present work studied different spermatozoa parameters and the ability of frozen rabbit spermatozoa to fertilize, it? vitro, in vivo-matured oocytes, as a test to predict their in vivo fertility and prolificacy. Semen from rabbit bucks was frozen using two freezing protocols [in a freezer at -30 degrees C or in liquid nitrogen vapour (LNV)]. For the in vivo trial, females were inseminated with frozen-thawed spermatozoa. Oocytes used for in vitro testing were recovered 14 h after ovulation induction from donors and co-incubated with 2 x 10(6) frozen-thawed spermatozoa during 4 h at 37 degrees C in Tyrode's medium under an atmosphere of 5% CO(2) in air with maximal humidity. After co-incubation period, presumptive zygotes were cultured in TCM199 supplemented with 20% foetal bovine serum (FBS), under the same conditions described above. Although no statistical differences were observed between freezing protocols in seminal parameters [motility rate: 40 and 35%, VCL 35 and 46 mu m/s, amplitude of lateral head displacement (ALH): 1.7 and 2.4 mu m, for semen frozen at -30 degrees C and in LNV, respectively], significant differences were noted in the fertilizing ability in vivo and in vitro. Semen frozen at -30 degrees C showed the highest fertilizing ability in vitro (26.7% vs 6.2 and 8.7% for semen frozen at -30 degrees C, in LNV and fresh semen, respectively) and the lowest fertility rate in vivo (21.7% vs 64.2% and 70.6% for semen frozen at -30 degrees C, in LNV and fresh semen, respectively). Sperm frozen at -30 degrees C seemed to be more capacitated.