Comparative study of preimplantation development and embryonic loss in two rabbit strains

The prolificacy of two rabbit strains (Californian and New Zealand) has been studied in parallel with ovulation rate and embryonic development. The number of mean ovulations was 11.6 in Californians and only 9.6 in New Zealand. In spite of the higher rate in the former, the number of young born was about 8 in both strains. Californian and New Zealand blastocysts were transferred at 96 h post-coitum by injecting them into the uterus of recipient does of the same strain or of the other strain (crossed transfer). The percentage of unfertilized and delayed eggs was significantly higher (20% vs 12%) in Californians. The size of blastocysts recovered at 96 h p.c. was significantly higher in New Zealand than in Californian does (370 vs 319 micron). The difference was due to the larger proportion of small Californian blastocysts and of large New Zealand blastocysts. The larger blastocysts were placed in the right horn of recipients and the small ones in the left horn. Number of foetuses at D27 showed that the survival percentage was always higher when large blastocysts were transferred. However the survival difference with small transferred blastocysts was not significant. When transfer was within the same strain or crossed the results were not different. Since the New Zealand blastocysts were larger at D4 p.c. (one day after they arrived in the uterus), it could not be determined if this improved development was due to the conditions in the fallopian tubes or to the quality of the uterine secretion.(ABSTRACT TRUNCATED AT 250 WORDS)