Improving equine oocyte quality to increase the efficiency of embryo in vitro production

Abstract

Recent advances in equine reproductive biotechnology have improved the in vitro production of embryos from immature oocytes collected from donor mares and abattoir-derived ovaries. This process involves oocyte aspiration, in vitro maturation (IVM), intracytoplasmic sperm injection (ICSI), embryo culture, and somatic cell nuclear transfer (SCNT) for cloning.

The main objective of this thesis was to evaluate different treatments aimed at improving equine oocyte quality and developmental competence. Results showed that oocytes obtained from donor mares had superior quality, leading to higher embryo development rates and a greater proportion of viable offspring compared with abattoir-derived oocytes.

Since oocyte quality is a major limiting factor in assisted reproduction, the studies focused on optimizing IVM systems. Different pre-IVM and IVM treatments were compared to determine their effects on oocyte maturation and subsequent embryo development following SCNT. Treatments designed to prevent the spontaneous resumption of meiosis during pre-IVM did not improve developmental potential. In contrast, supplementation of pre-IVM and IVM media with nicotinic acid (NA), a precursor involved in increasing NAD⁺ levels, significantly enhanced the ability of oocytes to develop into blastocysts.

Although additional studies are required to further clarify the role of meiosis-inhibiting treatments and confirm the beneficial effects of nicotinic acid, the findings presented in this thesis contribute substantially to the understanding of oocyte developmental competence in horses. Overall, this work provides valuable evidence for refining equine IVM systems and supports the development of improved protocols for in vitro embryo production in equids.