The embryo of a pig and a calf is studied under the field of Developmental biology. In this field, one is concerned about how the species grow and develop. For that, one must have the embryo of a pig and a calf.
The DNA of a pig and a calf is studied under the field of Molecular biology. This field deals with the study of the molecular composition of an organism, like the nucleic acids and proteins.
Both the limb structure of a calf and a pig is studied under the field of comparative anatomy. Comparative anatomy refers to the field of study, which deals with the similarities or differences between the structure and anatomy of distinct animals or species.