Recent advances in in vitro embryo production in small ruminants.

To increase productivity in the small ruminant industry, the genetic material of these species should be improved. In vitro embryo production could be an important technology to reach this goal by combining selected male and female gametes. In the world, marketing of in vitro-produced embryos is an economical activity which is progressing rapidly in cattle but is practically nonexistent in small ruminants. Since the birth of the first lamb and kid using IVF in the 80s, several studies have been carried out; however, results still are inconsistent and unpredictable. Moreover, significantly fewer research groups are working on embryo production in small ruminants than in cattle and pigs. Although conventional methodologies of oocyte IVM, IVF, and IVC in small ruminants give rise to blastocysts, significant variation exists between experiments. One important reason for these differences is the heterogeneity of the pool of oocytes recovered from ovaries from slaughtered females. Oocyte quality, also referred to as competence, is the key factor in the success of in vitro embryo production programs. Different criteria are used to select the best oocytes for fertilization, such as follicle size, oocyte diameter and morphological appearance, and Brilliant Cresyl Blue staining. New research lines aimed at improving oocyte competence are: (1) arresting nuclear maturation in vitro allowing optimal capacitation of cytoplasm, (2) growing oocytes inside the follicle, and (3) identification of biomarkers of oocyte competence in granulosa and cumulus cells and metabolites in the follicular fluid.