In vivo survival of mouse embryos frozen by direct plunging into liquid nitrogen and vitrification

Abstract

Ten nonlactating buffalo were superovulated with 3000 IU PMSG. Luteolysis was induced with 500 μg Cloprostenol (PG) 60 and 72 h after PMSG. Five buffalo were alloted for natural mating and five were bred by artificial insemination 60 and 84 h after the first PG treatment. Since four buffalo developed pyometra, only 6 of 10 underwent embryo collection successfully 180 to 190 h after PG. Three buffalo yielded only one morula each, while the remaining three yielded a total of two, three and four morulae and/or blastocysts as well als zero, one and three unfertilized ova, respectively. Six of the ten buffalo were assigned to an intensive blood collection regimen. Mean concentrations of progesterone (ng/ml) increased from 1.9 at PMSG stimulation to 4.8 at induction of luteolysis and decreased to a nadir of 0.2 about 72 h after PG treatment. The preovulatory surge of LH occurred 36 ± 9 h after PG and was low in magnitude (7.3 ± 1.3 ng/ml). Stimulation of 3 to 12 follicles resulted in concentrations of estradiol-17β exceeding 5 pg/ml within 48 h after PMSG treatment and reaching a maximum of 32 ± 11 pg/ml about the time of the preovulatory surge. Only in two individuals did concentrations decrease below 5 pg/ml within the following 12 h. In the other four buffalo 3 to 10 unovulated structures remained palpable, secreting estradiol-17β far exceeding the preovulatory concentrations. The fast appearing, low magnitude LH surges were key problems resulting from PMSG treatment. They caused unovulated endocrinologically active follicles. High estrogen levels during the early luteal period may activate subclinical uterine infections, which in turn may negatively affect embryonic development.