<i>In vitro</i> embryo production via ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) in pure and crossbred Japanese Hokkaido native ponies

This study evaluated the viability of in vitro embryo production using ovum pick-up (OPU) and intracytoplasmic sperm injection (ICSI) as breeding techniques for pure and crossbred Hokkaido native ponies (n = 9). Oocytes were collected using transvaginal ultrasound-guided follicle aspiration. ICSI was performed on in vitro matured oocytes using frozen semen. Embryonic cultures were monitored using time-lapse cinematography. Blastocysts were cryopreserved and, after thawing, were transferred non-surgically into recipient mares. Over nine OPU sessions, the mean number of aspirated follicles was 23.9 (range, 13-49). The oocyte recovery and maturation rates were 35.3% (76/215) and 61.5% (40/65), respectively. The cleavage rate was 57.5% (23/40). Of cleaved embryos, 56.5% (13/23) were arrested at the 4-cell to 8-cell stage, and five developed into early-blastocyst. Three embryos were transferred, resulting in a successful pregnancy. In conclusion, OPU-ICSI is a viable assisted reproductive technology for enhancing the population of Japanese native horses.