title: Comparison of survival rates of day 7 and day 8 bovine embryos after fast freezing and thawing.
abstract: The influence of fast freezing and thawing on bovine embryos at different stages of development was investigated. A total of 20 day-7 embryos and 37 day-8 embryos were thawed and classified morphologically before being transferred nonsurgically to synchronized recipients. Ninety percent (18 20 ) of the day 7 embryos (late morulae and blastocysts) were classified as transferable and a pregnancy rate of 52.9% (9 17 ) was obtained with these embryos. Seventy eight percent (29 37 ) of the day 8 embryos (expanded blastocysts) were classified as transferable, but only 24.1% (7 29 ) of these embryos resulted in pregnancy. The best pregnancy rate was obtained with the blastocysts of day 7 (5 8 or 62.5%), which compares favorably with that of freshly collected embryos. It is suggested that the low pregnancy rate found in the day 8 embryos is related to ultrastructural damages of the desmosomes and tonofilaments within the trophoblast layer, which results in a disturbance of the normal hatching process.
authors.affiliation: Institut für Tierzucht und Tierverhalten (FAL) Mariensee, 3057 Neustadt 1, Federal Republic of Germany.
authors.forename: H
authors.initials: H
authors.lastname: Niemann
authors.forename: W W
authors.initials: WW
authors.lastname: Lampeter
authors.forename: B
authors.initials: B
authors.lastname: Sacher
authors.forename: B
authors.initials: B
authors.lastname: Kruff