The survival of fertilized ova in gelled media in vitro was studied with the ovum transfer technique. A total of 1507 selected healthy ova of two to four or eight to thirty-two blastomeres was stored at 10° C in gelled media containing 7 %, 5 % and 1 % of gelatine in 1 : 1 serum : saline-solution for 4, 24, 48, 72, 120 and 144 hr. After storage, the ova were transferred to the Fallopian tubes of 115 recipient rabbits in a synchronous stage of pseudopregnancy. As controls, ova were stored for similar periods in liquid media of 1 : 1 serum : saline-solution mixture and ova were also transferred without storage. The recipients were laparotomized at 8 days post coitum (p.c.) to record implantations and were killed 15 days p.c. to count surviving embryos.
After storage for 4 hr in 7 % gelatine, the implantation rate of morulae was 72%. The percentage gradually declined until it reached 31% after 144 hr of storage. Implantation rate for ova stored in 7 % gelatine was slightly but consistently higher than for ova stored in liquid media for the corresponding periods. However, the difference was not statistically significant. Medium containing 1 % gelatine was superior to 5 % and similar to 7 % concentration.
Two- to 4-blastomere ova survived in gelled and liquid media from 4 to 48 hr at rates comparable with those of eight to thirty-two blastomeres. Storage in gelled media was superior to that in liquid media. After 72 hr of storage, the implantation rates of 2- to 4-blastomere ova in both gelled and liquid media were much lower than those of eight to thirty-two blastomeres.
Survival rate of morulae in gelled media was not improved in the presence of carbon dioxide. Slow warming after storage at low temperature was harmful to ovum survival. Serum was indispensable for ovum survival in gelled media. Embryo survival was the same for ova stored in gelled or liquid media. Embryonic survival of implantations from ova previously stored for 144 hr was significantly lower than that of ova stored for 4 to 72 hr. The use of autologous or heterologous serum did not change rates of implantation or embryo survival. The major morphological changes in the ova during storage were coarse granulation, loss of spheroid shape, lack of distinct blastomeres and the presence of a marked depression. The results are discussed in relation to physiological integrity of the ovum and functional defects occurring before or after implantation. The practical significance of the finding is discussed in relation to ovum transfer techniques in large animals.