Moderate distention of both uterine horns is evident. This could be a case of pyometra, which can be differentiated by palpation from an early gravid uterus by the absence of a membrane slip. In case of a pyometra the fluid can be displaced from horn to horn. Ultrasonographically, differentiation can be based on the absence of the embryo and the flocculent appearance of the fluid. In either case a corpus luteum will be present.
Vale WG (1987)