The FLI (Fat, F) and FHI (Lean, L) lines were developed by divergent selection over 60 generations on properties related to body fat. At the end of the selection experiment, the F-line had a high (~ 24) percentage of body fat and the L-line had only ~ 4%. Due to extreme in body fat these lines have poor reproduction and are hence endangered if maintained only by breeding. Another threat lies in the fact that breeding is only done at the Department of Animal Science, Biotechnical Faculty, University of Ljubljana in Slovenia and hence there is a possibility that in the case of diseases and disasters, these two genetic resources may be lost. Therefore, the main purpose of this Master’s thesis was to develop cryopreservation protocols for the potential need for line rederivation. In the first part, we wanted to optimize the protocol of female superovulation by optimizing the time interval between hCG and PMSG hormone application. In the second part, we tested protocols for in vitro production of two-cell embryos in line L, F, and control lines CD-1 and B6D2F1. 2-cell stage embryos were in vitro cultivated and frozen by vitrification. The embryos were thawed and cultured under in vitro conditions until the blastocyst stage. In line F, development stopped at the four-cell stage. For line L, however, in 3% of the two-cell embryos, development continued to the blastocyst stage. We were able to obtain up to 19% of weaned pups of L lineage, but these procedures failed for the F- line. In the second part of the Master's thesis we wanted to establish a protocol for cryopreservation of sperm in lines F and L, but despite modifications we were not able to develop an effective protocol. In summary, we were unsuccessful in cryopreservation of F lineage embryos and in sperm freezing procedures. In the selection line L, however, we succeeded in freezing the embryos and obtaining live pups after thawing, in vitro cultivation and embryo transfer.
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