Bone development in canine embryos and fetuses

The skeletal system plays essential roles during development, such as protecting vital organs, supporting muscles, enabling movement, and storing minerals. By the end of gestation, it also assumes a hematopoietic function through bone marrow activity. Despite its importance, data on skeletal development in dogs remain scarce. This study described the formation, chronology, and growth of the skeletal system in canine embryos and fetuses at different gestational stages. Uteri from pregnant bitches were collected during spaying campaigns and cesarean sections at the Veterinary Hospital of UEL. After exposing the embryos and fetuses, crown-rump length (CRL) was measured, and the individuals were divided into three groups: early (up to 20 days), mid (21-40 days), and late (41-60 days), with six individuals per group. Group I embryos underwent histological analysis using hematoxylin and eosin (H&E) staining to identify pre-osseous structures. Skeletons from Groups II and III were stained with Alizarin Red and Alcian Blue and subjected to radiographic examination. From day 27, ossification centers were observed in the frontal bone, humerus, and femur. Over time, new centers emerged in the mandible, ribs, vertebrae, and other long bones. As gestation progressed, these centers expanded toward the epiphyses; although, regions such as the patella and vertebral extremities remained cartilaginous. These findings contributed to the understanding of normal skeletal development in dogs and support future studies on congenital skeletal disorders.