Most wild equids are currently endangered or threatened, as mentioned in the International Union for the Conservation of Nature Red List, and several domestic horse breeds are at risk of extinction. Genome resource banking requires cryoconservation of semen, oocytes, and/or embryos. Embryo production in equids is limited in vivo because routine induction of multiple ovulation is still ineffective. Embryo production in vitro allows the production of several embryos per cycle that could easily be frozen because of their small size. Intracytoplasmic sperm injection has been widely adopted to generate horse embryos in vitro; however, intracytoplasmic sperm injection is time-consuming and requires expensive equipment and expertise in micromanipulation. Several attempts to establish an efficient IVF technique in the equine were performed, but reported IVF rates remain quite low and no repeatable equine IVF technique was available. Our objective was to develop an efficient and repeatable IVF technique in the equine. Immature cumulus-oocyte complexes (COC) were collected either from slaughtered mares in a local slaughterhouse or from our experimental mares by ovum pick up (OPU). The COC were cultured for 26 h in an in vitro maturation (IVM) medium or in preovulatory follicular fluid (FF) collected by OPU, pre-incubated for 30 min in oviducal fluid collected from slaughtered females, co-incubated for 18 h with fresh spermatozoa treated with procain, and cultured in SOF for 30 h. They were fixed and analysed either after 18 h IVF (experiment 1) or after 30 h in vitro development (experiment 2). In experiment 1, COC were collected from slaughtered mares and analysed after 18 h IVF. Zygotes with 2 pronuclei were observed. The IVF rate was similar for oocytes matured in IVM medium (22/33, 67%) or FF (24/42, 57%; chi-square test, P > 0.05). In experiment 2, COC were collected from slaughtered mares and from experimental mares and analysed after 30 h of in vitro development. We observed zygotes with 2 highly decondensed pronuclei, pronuclei decondensation being the first step of embryo development. For oocytes collected from slaughtered mares, the percentage of zygotes was similar for oocytes matured in IVM medium (8/11, 73%) or FF (10/15, 67%). For oocytes collected by ovum pickup, the percentage was similar for IVM medium (3/5, 60%) or FF (6/8, 75%). We also observed some embryonic structures with several nuclei, but the quality of these embryos was poor. In conclusion, we have established an efficient IVM-IVF technique that allows the first step of embryo development. Because we obtained similar results for 4 years, we consider that this efficient technique is repeatable. Further experiments are in progress to improve the quality of the embryos.
In vitro development of bovine oocytes collected from ovaries of individual cows after in vitro fertilization.
