Today, although not efficient enough to replace multiple ovulation and embryo transfer, in vitro embryo production for small ruminants is a platform for new reproductive technologies, such as embryo sexing, transgenesis and cloning. The in vitro embryo-production system developed for sheep and goats is more efficient now than 15 years ago, but could still be improved. Laparoscopic collection of oocytes in live animals treated with gonadotrophin indicates a promising future for the application of this technology to genetic improvement programmes. Oocyte maturation in defined medium with epidermal growth factor and cysteamine appears as efficient as oocyte maturation in follicular fluid-supplemented medium and allows future study of the effect of other factors involved in the cytoplasmic maturation of oocytes from these species. Further efforts have to be made to standardise the semen-capacitating process and to improve the quality and freezability of in-vitro-produced (IVP) embryos. The optimisation of IVP procedures for deer species has required the study of the seasonal variation of oocyte competence and the development of a specific methodology to allow the culture of embryos up to the blastocyst stage.
In vitro fertilization (IVF) gives rise to embryos in a number of mammalian species and is currently widely used for assisted reproduction in humans and for genetic purposes in cattle. However, the rate of polyspermy is generally higher in vitro than in vivo and IVF remains ineffective in some domestic species like pigs and horses, highlighting the importance of the female reproductive tract for gamete quality and fertilization. In this review, the way the female environment modulates sperm selective migration, survival and acquisition of fertilizing ability in the oviduct is being considered under six aspects: (1) the utero-tubal junction which selects a sperm sub-population entering the oviduct; (2) the presence of sperm binding sites on luminal epithelial cells in the oviduct, which prolong sperm viability and plays a role in limiting polyspermic fertilization; (3) the contractions of the oviduct, which promote sperm migration toward the site of fertilization in the ampulla; (4) the regions of the oviduct, which play different roles in regulating sperm physiology and interactions with oviduct epithelial cells; (5) the time of ovulation and (6) the steroid hormonal environment which regulates sperm release from the luminal epithelial cells and facilitates capacitation in a finely orchestrated manner.
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