ICSI equine embryo production with oocytes aspirated during estrus or diestrus

Abstract

Intracytoplasmic sperm injection (ICSI) has advanced equine reproduction using genetically superior or imported semen, enabling older mares with fertility issues to foal again or make use of vitrified embryos facilitating embryo transfer. One focus of our lab is to maximize embryo production by increasing rates of oocyte recovery and maturation which have resulted in a greater number and rate of blastocyst development. One variable is the stage in the ovarian cycle, estrus or diestrus, when ovum pickup (OPU) is performed. The OPU technician evaluates if the mare is in estrus or diestrus just prior to OPU as following: estrus is identified as the presence of a dominant follicle, uterine edema and upon uterine palpitation, there is weak uterine tone. Diestrus is identified with the presence of a corpus luteum without the presence of uterine edema and a firm uterine tone. We analyzed 3,686 sessions of OPU between July 2021 toNovember 2022 in our commercial program. A total of 14,993 follicles were aspirated with 1,682 OPU sessions in the estrus phase and 14,627 follicles from 2,004 OPU sessions in the diestrus phase. A total of 13,240 (7.6 oocytes per OPU) oocytes were recovered in the estrus phase and 12,985 (6.4 oocytes per OPU) in the diestrus phase. A total of 15,588 oocytes were injected, 7,857 from estrus phase follicles and 7,731 from diestrus phase follicles. In the estrus phase, 2,269 (17%) embryos were produced from all oocytes, while in the diestrus phase, 2,109 (16%) embryos were produced from aspirated oocytes (Chi square p>0.05). There was no significant difference in oocyte retrieval (88%) or embryo production rates according to cycle phase of the donor mare. These results corroborate previously published results (Walbornn et al. Journal of the American Veterinary Medical Association.2022; 260 (7):1-7).