To examine various medications and substances, in vivo models such as rats and mice are routinely used. However, it is utterly desirable to reduce extensive amounts of animals for these experimental models, which are costly and time-consuming. Animals are frequently put through a variety of procedures that could cause them pain, distress, or even harm
therefore, it is important to think about the ethical ramifications of using them in research. Thus, by following the three R's of animal research: reduction, replacement, and refinement, living animals used in studies should be minimized. The embryo of Gallus gallus, the domestic chicken, is a great model to research many different diseases and conditions. Its efficient blood supply from the chorioallantoic membrane gives us a unique possibility to administer chemicals or cells to the embryo in a noninvasive manner. In this review, we evaluate some advantages and disadvantages of using the developing chicken as an alternative in vivo model for development, disease, and pharmacological treatment. We focus on the top two leading causes of death: neurological disorders and cancer. We present a number of studies that describe the use of the chicken embryo in neuroscience and neurodevelopment research, in cancer research, and pharmacodynamic and pharmacokinetic studies. These studies show that the chicken embryo is an inexpensive, readily available, self-sufficient model with a short incubation period, high accessibility, and ideal for drug screening, making it an appealing model that can provide insightful biological and pharmacological information.