ABSTRACT
The development of fertilized rabbit eggs trapped in the oviduct by ligation was examined at 84, 96, 108 and 120 h p.c. in ten animals, five of which were superovulated. Out of 210 eggs recovered, only two failed to develop into early blastocysts. The proportion of blastocysts undergoing some expansion increased from 66% at 84 h to 100% from 96 h onwards, when a high proportion, 66-89%, had ruptured zonae pellucidae. The viability of the blastocysts was assessed by transfer to the uteri of recipient rabbits, in which the proportion developing to term fell from 62% at 84 h to 3% at 108 h.
A total of 643, 2- and 4-cell eggs recovered 30 hp.c. was transferred to the ligated oviducts of oestrous, early or mid-luteal does for periods of 24, 48 or 72 h. Development to the early blastocyst stage appeared to be faster in the luteal phase than in oestrous does. Of the eggs recovered after either 48 h or 72 h, 20-40% and 3-17% respectively were capable of developing to term. In general, the less advanced blastocysts survived better.
Three hundred and twenty-one 60 h morulae were transferred to the ligated oviducts of oestrous or mid-luteal does for 24,48 or 60 h. Neither the rate of egg development nor viability was significantly affected by the endocrine status of the temporary recipient. The proportions of eggs developing to term after transfer to recipients were 50%, 20% and 0%.
It is concluded that the rabbit egg cannot develop beyond the early blastocyst stage in the oviduct, irrespective of the host’s endocrine status. If development is interrupted, the life-span of the blastocyst is very short. The rabbit blastocyst requires to undergo almost continuous development to differentiate normally.