In vivo versus in vitro embryo production in small ruminants: strengths, limitations, and practical outcomes.

Embryo transfer technologies have become essential tools for accelerating genetic gain, disseminating superior genetics, and preserving valuable germplasm in livestock species. In small ruminants, embryo production has historically relied on multiple ovulation and embryo transfer (MOET), whereas in vitro embryo production (IVEP) has expanded substantially over recent decades. Despite this technological progress, the global embryo industry in sheep and goats remains dominated by MOET systems, in contrast to cattle, where IVEP has rapidly become the prevailing technology. This review critically examines the biological, technical, and logistical factors underlying the current balance between MOET and IVEP in small ruminants. We discuss the main biological determinants influencing embryo production efficiency, including oocyte developmental competence, species-specific reproductive traits, and the intrinsic sensitivity of small ruminant gametes and embryos to in vitro environments. A comparative analysis with bovine systems highlights that several operational advantages that have driven the expansion of IVEP in cattle, such as the possibility of repeated ovum pick-up without hormonal superstimulation, minimally invasive oocyte recovery, and efficient use of sex-sorted semen, are not readily transferable to sheep and goats. Conversely, recent advances in nonsurgical embryo recovery have reinforced the practical advantages of MOET in small ruminants by reducing procedural invasiveness and improving animal welfare. Emerging perspectives for IVEP are also discussed, including innovations in embryo culture systems and the integration of IVEP with genomic selection and sexed semen technologies. Overall, current evidence indicates that the predominance of MOET in small ruminants reflects not a technological delay but rather a complex interplay of biological robustness and operational simplicity. We believe that IVEP is more likely to expand as a complementary tool rather than to replace MOET as the dominant embryo production strategy in sheep and goats.