Effect of slow cooling end point temperature on survival of frozen bovine embryos.
One hundred sixty-two embryos were collected from superovulated crossbred beef cattle 7 to 8 d after the onset of estrus. Embryos were frozen in modified Dulbecco's phosphate-buffered saline supplemented with 20% heat-inactivated fetal calf serum (PBS + FCS) and dimethylsulfoxide (DMSO), which was added in three steps to a final concentration of 1.5 M. Embryos were placed in .25 ml of 1.5 M DMSO in PBS + FCS in 1-ml glass ampules and cooled at 1.0 C/min from ambient temperature to -7 C, seeded and then cooled at .3 C/min to -19, -26, -33, -38, -43, -50 or -57 C before immersion (plunging) in liquid nitrogen. Ampules were thawed in 25 C water, and DMSO was removed in six steps at .25 M increments. 10 min/step. After removal of DMSO, embryos were cultured 24 h in PBS + FCS and then fixed and stained. Just after thawing, embryos for which slow cooling was terminated at -50 C were of lower (P less than .05) morphological quality than other groups. After removal of cryoprotectant, embryos from both the -19 and -50 C treatments had deteriorated more (P less than .05) than had embryos from other treatments. After 24-h culture, embryos slow-cooled to -19, -26 and -50 C had a lower rate of survival (P less than .05) than did embryos from -33, -38, -43 and -57 C temperatures. Embryos slow-cooled to -33, -38 and -43 C showed a higher percentage of healthy nuclei than did embryos slow-cooled to -19, -26 and -50 C.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001755:Blastocyst / Q000502:physiology / Q000648:ultrastructure; D002417:Cattle / Q000196:embryology*; D002467:Cell Nucleus / Q000648:ultrastructure; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004622:Embryo, Mammalian / Q000502:physiology*; D005615:Freezing; D008938:Mitosis; D009028:Morula / Q000502:physiology / Q000648:ultrastructure; D013696:Temperature; D014021:Tissue Preservation / Q000379:methods / Q000662:veterinary*
D004121:Dimethyl Sulfoxide