Effect of clinically-related factors on in vitro blastocyst development after equine ICSI.

This research article investigates some factors that potentially influence the efficiency of equine intracytoplasmic sperm injection (ICSI), a practice used to produce foals. The research includes several experiments that investigate different variables, such as time delays between transvaginal ultrasound-guided follicle aspiration (TVA) and isolation of oocytes, the effects of antibiotics on oocyte quality, the influence of stallion differences on cleavage rates, and efficiency considerations throughout the year.

Time Delays and Oocyte Processing

• The researchers performed a series of studies observing how time delays between TVA, a method used to recover oocytes, and the isolation of the oocytes impacted blastocyst development (early stage embryos).
• The initial study showed that a 1.5 hour delay at ambient temperature resulted in a 32% yield of blastocysts, relatively robust for the species.
• However, the first official experiment revealed a decrease in blastocysts yield when the waiting time was extended to 2 hours (under constant temperature of 32°C) compared to immediate processing. The difference indicated that prompt isolation of oocytes from the aspirated fluid is beneficial for blastocyst development.

Seasonal Variations and Antibiotics Use

• The second experiment focused on the study of follicle numbers throughout the year and the potential impact of antibiotics on the quality of the oocytes.
• Follicle numbers at the time of TVA were found to be higher during the winter, and oocyte recovery rates remained relatively consistent.
• Antibiotics administration before TVA, which is performed to reduce the possibility of infection, did not negatively impact blastocyst rate, suggesting this measure is safe in these conditions.

Stallion Differences and Sperm Preparation Methods

• The third experiment identified that different stallions could produce varying rates of cleavage after performing an ICSI procedure on their motile sperm samples.
• By improving the sperm preparation process with a combination of density-gradient centrifugation and swim-up, better rates of cleavage and blastocyst development were achieved with sperm from a low-performing stallion.

Parthenogenetic Activation and Effects of Sperm Damage

• In the fourth experiment, the researchers used parthenogenetic activation, a method to artificially stimulate an egg to start developing as if it was fertilized, and achieved a high blastocyst yield.
• Attempts to generate blastocysts using immotile sperm damaged by a nitrogen tank failure proved unsuccessful, regardless of using exogenous activation after ICSI. This implies the importance of sperm motility for successful blastocyst formation.