Suitability of emu (Dromaius novaehollandiae) eggs for in ovo imaging research as an alternative to conventional animal model: First experience and non-invasive investigation of physiological embryonal development on computed tomography

Fertilized bird eggs are an alternative model to conventional animal testing. In recent studies, a preclinical imaging model based on large ostrich eggs was introduced in a clinical research centre using imaging systems designed for humans, thus bypassing the need for dedicated small animal imaging systems. Ostrich eggs are only laid during the season with increased daylength, which limits its year-round availability. The current study focuses on large emu eggs instead of ostrich eggs and aims at investigating its suitability for preclinical imaging research. Physiological development of emu embryos was observed by serial weightings and serial CT scans until developmental day (DD) 46. Differences between fertilized a non-fertilized eggs were analysed. In fertilized eggs, the embryo was identified on CT scans as early as DD 13. As expected, CT scans showed continuous embryonal development and growth over time, comparable to ostriches. Neither the eggs' volume and weight nor the weight loss nor the radiodensity provided significant differences between fertilized and non-fertilized eggs. Despite inferior incubation success in emus compared to ostriches, suitability of emu eggs for artificial incubation and subsequent research was confirmed. Hence, emu eggs represent an alternative model for preclinical imaging and allow a year-round use for research purposes if combined with ostrich eggs.