Factors influencing the intracytoplasmic sperm injection (ICSI) efficacy in goat and sheep

Abstract

Intracytoplasmic sperm injection is performed by microscopically injecting a sperm cell into an egg cell's ooplasm effectively bypassing usual steps taken in natural reproduction. ICSI in goats and sheep provides opportunities for better genetic selection to improve small ruminant production potentially. It has also shown promise for wildlife conservation by preserving spermatozoa from endangered species. Different factors that affect the success rate of ICSI in sheep and goats have been categorized into external and internal factors. Reproductive seasonality suggested that oocyte harvest can be done year-round but efficient oocyte development occurs during breeding (autumn) season. Superovulation is induced in goats and sheep via administration of follicle stimulating hormone (FSH), luteinizing hormone (LH), equine chorionic gonadotropin (eCG), and pregnant mare serum gonadotropin (PMSG). Toxins accumulating around the ICSI-produced embryo such as free radicals and ammonium ions has led to embryonic arrest. Female animals cannot be juvenile nor geriatric to be able to produce viable oocytes for ICSI procedures. Donor animals with proper nutrition and ideal weight produced high quality oocytes. Boer goats were found to be polyestrous and sensitive to hormonal treatment making them the ideal breed for ICSI. Proper sourcing and management of the oocyte has greatly affected success rates of ICSI. Fresh sperm from male donor animals produced more blastocysts than frozen-thawed sperm. Frozen-thawed sperm however has shown excellent membrane integrity important for ICSI-embryo development. Immobilizing sperm by breaking the tail before ICSI has increased blastocyst yield. ICSI success rates are affected by external and internal factors responsible for sex gamete quality.