First deliveries of felines by transcervical transfer of in vitro-cultured embryos

Transcervical transplantation of embryos has been wildly used in several species. However, it has not been successful in feline species because of their unique cervix structure combined with poor in vitro culture systems for embryos. In the present study, a simple device to guide the embryo transfer (ET) tube through the cervix and into the uterus was developed. To supply better blastocysts for ET, the in vitro culture system of feline embryos was also optimized. Results showed that 91.67 ± 4.17% of embryos developed to the blastocyst stage in QAU-4 medium compared with 49.17 ± 6.51% in KSOM medium. The total cell number of blastocysts reached 87.1 ± 22.1 in QAU-4 medium compared with 29.8 ± 2.1 in KSOM. Embryoid body formation was also observed in QAU-4 medium. Finally, by the improved technical scheme, CRX (Cone-Rod Homeobox) gene-edited kittens were successfully bred. To date, this is the first report, to our knowledge, of knockout kittens successfully delivered after transcervical ET with a simple transfer tube.