Live cubs born after transfer of OPS vitrified-warmed embryos in the farmed European polecat (Mustela putorius)

The Open Pulled Straw (OPS) method of vitrification has been used successfully for cryopreserving embryos of most domestic animal species. However, there is no report of a successful delivery of offspring after transfer of vitrified embryos in carnivores, even though vitrification has been a successful freezing method for species like swine whose embryos are known to be susceptible to chilling injury. Morulae and blastocysts of farmed European polecat (Mustela putorius) were vitrified and warmed before in vitro culture in modified synthetic oviductal fluid (SOF) for a period from a few hours up to 3 days before being transferred to recipients. Survival rate after vitrification, warming and in vitro culture was 51% (50/98). A total of 50 embryos were transferred surgically into the uteri of four anesthetized recipients. Two recipients delivered a total of eight offspring (2 and 6 each) for an overall survival rate of 16% (eight live cubs/50 transferred embryos). According to our knowledge, these offspring are the first carnivores produced by transfer of in vivo embryos after vitrification by OPS. Based on the present results, we suggest that OPS vitrification can be used as an alternative cryopreservation method for mustelid embryos with pup results comparable to conventional slow freezing.