High Culturing Humidity Improves Ex ovo Chick Embryo Viability

The chorioallantoic membrane (CAM) of the developing chick embryo is a highly vascularized system able to be used for many applications. However, published protocols for the ex ovo model were found to be inconsistent and confusing, especially regarding the ideal relative humidity (RH) for chick embryo incubation. Some publications have suggested that a lower RH results in lower embryonic viability compared to that of higher RH, however, no systematic testing regarding the effect of RH on ex ovo chick embryo viability has been reported. The goal of this project is to confirm the importance of RH on embryonic viability in addition to exploring the variables responsible for such importance in order to help standardize the protocol used in the ex ovo CAM field. Trials were conducted through comparing the viability of embryos cultured in previously published novel vessels vs plastic tumbler vessels that were placed in an incubator with either low relative humidity (60% RH) or high relative humidity (80% RH). Our findings suggest that higher RH has a positive impact on embryonic viability. We also note that water evaporation may play a role impacting the viability of the embryo, due to a significant loss of mass over time in ex ovo chick embryos cultured in lower RH compared to higher RH