Development of external morphological malformations induced by hyperthermia exposure during the blastula stage in an ex-ovo (shell-less) culture of Gallus gallus domesticus embryos

The chicken is a valuable model to study embryonic development, genetic manipulation, regenerative medicine, tumorigenesis, vaccine development, toxicology, and teratology research. Different methods have been described for incubating chicken embryos outside the eggshell (ex-ovo or shell-less incubation). To date, no studies have focused on using ex-ovo incubation as a model to study the effects of hyperthermia as a teratogen. In this work, a total of 350 fertile chicken eggs were used to study the development of congenital malformations in an ex-ovo and in-ovo incubation system exposed to normal (37.5°C) and hyperthermia conditions (40°C). In the ex-ovo hyperthermia test, all ex-ovo embryos (n = 50) developed malformations; only 0.02 % reached 5 days of development. In the ex-ovo normal temperature group, none of the ex-ovo embryos developed malformations, and 48 % reached 21 days of development; there was no significant morphological difference between the ex-ovo normal temperature and the in-ovo normal temperature group. The time of exposure to hyperthermia conditions is crucial for the development of malformations, with the blastula stage (0 h) being the most susceptible. Blastula stage malformations, neural tube defects, microphthalmia, amelia, gastroschisis, caudal regression, and the development of twinning were identified. The ex-ovo incubation system does not increase the risk of the development of malformations, and it is a viable model for studying the effects of teratogens, as well as the morphology and physiology of the embryo.