Relationship of age at parabiosis and time of embryonic death on extent of mixing of embryonic blood.

Two studies were conducted to determine the extent of blood chimerism from parabionts joined at different ages and the mortality pattern after joining. Complete mixing of blood was found in 100% of the pairs joined at 13 days, 80% at 15 days, and 25% at 17 days of incubation. Therefore, interfusing of blood components could only be assured when the embryos were joined no later than 13 days of incubation. Mortality after parabiosis occurred in three peaks. The first and largest peak (16.4% mortality) occurred at 12 hr after parabiosis with substantial mortality through 36 hr. The second peak (4.6% mortality) occurred between 108 and 120 hr after joining of the eggs. The third and final peak (5.6% mortality) occurred between 192 hr and hatch. Surgical trauma, bacterial contamination, and the inability of the embryo to escape the shell once pipped are possible explanations since these events were associated with clusters of embryo deaths. The use of single surviving parabiont as a means of increasing the efficiency of the parabiotic technique is discussed.