Discovery and characterisation of the first menstruating rodent: The spiny mouse for use as an in vivo model of reproductive biology BELLOFIORENADIA 2019 This thesis details the discovery of the only naturally menstruating rodent, the spiny mouse. While reproduction in every other rodent is dictated by the environment and, importantly, the lining of the womb is not shed, the spiny mouse behaves like humans, and cyclically menstruates. The menstrual cycle lasts only 9 days, although shares many aspects with the 28-day human cycle. Each animal is unique in the length and heaviness of their menstrual period, the degree of inflammation and fluctuation of physical parameters (i.e. food consumption and body weight). This world first discovery advocates for the spiny mouse to be recognized for its extraordinary potential in studying women’s reproductive health and menstrual associated conditions.