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Oviduct as well as oocyte and embryo development are subject to developmental changes which have crucial effects on the application of in vivo culture. The present study aimed at optimizing in vivo culture of IVP bovine embryos at different developmental stages in the bovine oviduct. Cumulus oocyte complexes (COC) were collected from slaughterhouse ovaries, matured in vitro for 22 h and assigned to four groups. In groups I and II, oocytes were pre-incubated for 3 to 4 h with 5 × 106 sperm/mL, and then immediately transferred to recipients, which had just completed ovulation (group I), or kept in vitro for a further 12 to 18 h and transferred to Day 1 synchronized recipients (group II). In groups III and IV, COC were subjected to standard IVF/IVC; then embryos were either transferred at the 4- to 8-cell stage on Day 3 into the oviducts of Day 3-synchronized recipients (group III) or kept in vitro for a further 4 to 5 days (group IV). Thirty-four 18- to 30-month-old temporary recipients were synchronized using a standard Ovsynch protocol. COC and embryos were transferred and re-collected by transvaginal endoscopy. COC or embryos were loaded into a 180° curved glass capillary, which was inserted via the infundibulum 5 to 8 cm deep into the ampulla ipsilateral to the CL. On recipient Day 7, a 90° curved metal canula served for tubal flushing prior to conventional uterine embryo flushing. Sixty mL of PBS containing 1% fetal calf serum were rinsed through the oviduct into the uterus and a further 400 mL of medium were finally used for flushing of the uterine horn and collected via an embryo filter. Embryo development was evaluated directly after flushing (Day 7) and on Day 8. For statistical analysis (ANOVA), the blastocyst rates (Days 7 and 8) in group III were related to COC corrected by the collection rate. In group I, 575 COC were transferred to 11 recipients and 420 (73%) were re-collected as oocytes or embryos. The blastocyst yields on Day 7 and Day 8 were 23% (97) and 25% (104), respectively. In group II, the transfer of 489 presumptive zygotes into 13 heifers resulted in only 175 re-collected (36%), of which 15% developed into blastocysts (Day 7: 26; Day 8: 27). Ten heifers (group III) served for in vivo culture of 643 embryos at the 4- to 8-cell stage. On Day 7, 568 (88%) embryos were flushed and 171 (30%) reached the blastocyst stage. A further 24 h culture in vitro finally resulted in 244 (42%) blastocysts. The complete in vitro production system delivered 13% (63/477) blastocysts on Day 7 and 34% (161/477) blastocysts on Day 8. The collection rates (P &lt; 0.001) and the blastocyst rates on Day 7 (P &lt; 0.05) and Day 8 (P &lt; 0.001) differed significantly in all groups. The present data demonstrate that the developmental stage of transferred complexes has an influence on embryo recovery as well as an embryo development.This work was supported by Austrian BMBWK and BMLFUW (#1227).

160 IN VIVO-CULTURE OF BOVINE EMBRYOS: TRANSFER OF SEMEN PRE-INCUBATED OOCYTES, ZYGOTES AND 4 TO 8 CELL STAGE EMBRYOS INTO THE BOVINE OVIDUCT