In the past decades, there have been tremendous changes in equine reproduction. Assisted reproductive techniques (ART) for horses, such as in vitro oocyte maturation (IVM) and in vitro fertilization (IVF), has been slow and with low success rates compared to other domestic species. The unique characteristics of equine oocytes such as morphology, gene expression, and developmental potential make it challenging to develop standardized IVM and IVF protocols. The aim of this review was to address all aspects of the current knowledge of IVM and IVF in horses.

Objective: The objective of this study was to evaluate the effects of caffeine and taurine on the motility and viability of chilled equine semen. Materials and Methods: A total of 12 ejaculates were collected from three mature stallions with proven fertility during the breeding season. The gel-free spermatic fraction of each ejaculate was divided into two aliquots and diluted with a semen extender (either INRA 96® or BotuSemen Gold®). The aliquots were then split and assigned to one of the six treatment groups: control (no supplement), caffeine (2 and 4 mM), taurine (25 and 50 mM), and a combination of caffeine (2 mM) plus taurine (25 mM). Samples were stored at 4°C and analyzed at different time points (0, 24, 48, 72, and 96 h) to evaluate total (TMOT) and progressive (PMOT) motility and viability by computer-assisted sperm analysis. Results: Regardless of the extender, PMOT and TMOT decreased over time. However, compared with the control, the treatment with 4 mM caffeine significantly mitigated the decrease in PMOT at 72 h. Additionally, semen treated with a combination of caffeine plus taurine maintained a significantly higher PMOT at 96 h, with improved viability at all time points. Conclusions: The combination of caffeine plus taurine helps maintain chilled equine semen viability and progressive motility up to 96 h independently of the extender used.