Morphological Description of the Developing Ostrich Embryo: a Tool for Embryonic Age Estimation

The ostrich (Struthio camelus), the largest living bird, is farmed intensively worldwide. However, despite the importance of understanding embryonic development in the ostrich for successful egg incubation practice, little is known about it. Using the chicken model for scaling is currently a common practice in estimating age in ostrich embryos. The aim of this study was to compare the embryonic morphological development of the ostrich to that of the chicken, as both physiological and morphological differences in the embryonic development of the two species have been reported recently. Ostrich eggs were incubated at 36.5 °C and 25% relative humidity. The embryos were inspected on alternate days from day 4 through day 40 of incubation. The study showed that the temporal appearance of structures in the first half of the embryonic development of the ostrich resembles that of the chicken. However, differences in the temporal appearance of grooves between toes and digits, nictitating membrane, eyelid covering of the eyeball, and the appearance of scales on the legs appear to exist between the two species, but their confirmation will require the use of larger egg samples. The second half of the development was described by changes in the beak, wing, and leg lengths, as well as by that of the embryo’s wet mass. Since the growth patterns of the ostrich and the chicken differ, embryonic age estimation of one species cannot be inferred from relative changes in linear dimensions of the other. We offer equations for estimating the embryonic age of the ostrich during the second half of incubation using morphometric measurements of the above parameters.