Meiotic Status Does Not Affect the Vitrification Effectiveness of Domestic Cat Oocytes

Abstract

Cryopreservation is important for animal fertility and biodiversity. Unfortunately, cryopreservation of feline oocytes is still an experimental technique. The aims of this study were to analyze the potential toxicity of the cryoprotectants in the vitrification solution (VS) on cat oocytes and to investigate whether the meiotic status of oocytes influences their developmental potential after vitrification. Two experiments were conducted with the VS composed of 20% ethylene glycol, 20% dimethyl sulfoxide, 20% fetal calf serum, 1.5 M trehalose, and 10% Ficoll PM-70: (1) toxicity assessment of the VS on immature cumulus oocyte complexes (COCs), and subsequently in vitro maturation (IVM) and in vitro fertilization; (2) assessment of the influence of the meiotic status on vitrification effectiveness, where immature and in vitro matured COCs were vitrified on the Cryotop. After rewarming, vitrified oocytes were subjected to IVM (immature) and intracytoplasmic sperm injection (ICSI) with fresh epididymal sperm. The toxicity test revealed no negative effect of oocyte exposure to the applied VS on their developmental potential (p > 0.05). Although the vitrification procedure itself significantly reduced the meiotic competence of oocytes, their meiotic status before vitrification (immature vs. in vitro matured) did not influence fertilization and morula rates. The only parameter affected by vitrification was the rate of oocytes suitable for ICSI, which was significantly lower for immature oocytes. Regardless of the meiotic status of vitrified oocytes, morphologically normal morulae were obtained. Moreover, the two meiotic stages examined are suitable for vitrification, with mature oocytes being a better choice when a well-equipped laboratory is available.

Comparison of Different Materials for Self-Pressurized Vitrification of Feline Oocytes—First Results

“…Thus, COCs were inserted in the tubes with WM (control) or together with the vitrification solution but for a shorter time, 2 min. There was no control on the effect of CPAs alone with COCs since this possibility has been previously studied, demonstrating no toxic issues [ 24 ]. Later oocyte competence was analysed in terms of maturation success and cleavage after fertilisation.…”

Oocyte Cryopreservation in Domestic Animals and Humans: Principles, Techniques and Updated Outcomes

“…Using conventional slow freezing, MII oocytes are significantly more tolerant to slow freezing compared with immature oocytes when cryopreserved slowly with ethylene glycol (cleavage rate 6.8% vs. 38.7%) [129]. Similarly, the cleavage rate of vitrified-warmed feline mature oocytes is slightly higher than that of the immature counterparts (21% vs. 4%) [130]. Development of the cryopreservation of feline oocytes focused on the use of vitrification yielded 0-10% blastocyst rates [54,55,[131][132][133][134].…”

IGF-I Medium Supplementation Improves Singly Cultured Cat Oocyte Maturation and Embryo Development In Vitro

“…In Experiment A, IVM (a total of 420 COCs) took place in group culture as previously reported [42], and after fertilisation by IVF two different types of culture were tested: single and group, referred to three zygotes per group. For both groups, different supplementation was applied to IVC, and five treatments were tested: (1) control group, (2) the addition of IGF-I at the concentrations 10 ng/mL; (3) the same with 20 ng/mL IGF-I, (4) the addition of GM-CSF at 2 ng/mL alone, or (5) in combination with a low dose of IGF-I corresponding to 10 ng/mL.…”