Comparison of survival rates of day 7 and day 8 bovine embryos after fast freezing and thawing.
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.
Niemann
H
H
Institut für Tierzucht und Tierverhalten (FAL) Mariensee, 3057 Neustadt 1, Federal Republic of Germany.
Lampeter
W W
WW
Sacher
B
B
Kruff
B
B