Generating cloned sheep embryos by zona-free somatic cell transfer

This protocol summarises zona-free sheep cloning by somatic cell transfer (SCT), adapted from a similar SCT method in cattle (https://doi.org/10.1089/153623003772032763). It describes the workflow that is required for reprogramming somatic cells into cloned blastocysts of high morphological quality, including two optional steps of embryo aggregation and vitrification. The resulting embryos can then be transferred into surrogate ewes for producing live cloned animals. Compared to conventional zona-intact procedures, this zona-free embryo reconstruction system increases throughput of cloned embryo production and ease of operation.