At what gestational age can fetal skeletons be first observed on abdominal radiographs in dogs?

Fetal skeletons can first be observed on abdominal radiographs in dogs starting at 43 days of gestation. At this stage, ossification has progressed to a point where the bony structures of the developing fetus are sufficiently mineralized to be detectable on X-rays. Early in gestation, specifically around 23 days, the skeletal structures are not yet developed enough for imaging, as the bones have not completed their ossification process. By 33 days, while some development is occurring, the skeletal formations remain too soft and not well-defined for radiographic visualization. It isn't until 43 days that the components of the skeleton are adequately formed to be seen clearly on an abdominal radiograph, making this the correct answer regarding when fetal skeletons can first be observed.