Fetal Growth and Osteogenesis Dynamics during Early Development in the Ovine Species

SIMPLE SUMMARY: Our study represents an innovative attempt to describe fetal skeleton development during the first part of gestation in sheep using ultrasonography associated with a differential staining technique that allows the observation of the first ossification processes. The timing of ossification and the growth rate of skeletal components are very important to assess normal prenatal growth. This knowledge may be useful for gestational management and early diagnosis of skeletal diseases, especially in the early period of pregnancy when bone growth is very fast in the ovine species. ABSTRACT: Increased knowledge of the developmental processes during gestation could provide valuable information on potential alterations in embryonic/fetal development. We examined the development of ovine conceptus between the 20th and 70th day of gestation with three convergent analyses: (1) uterus ultrasound examination and measurement (eco) of crown–rump length (CRL) and biparietal diameter (BPD) of the conceptus; (2) direct measurement (vivo) of CRL and BPD of the conceptus outside the uterus (3) osteo–cartilage dynamics during development by differential staining. No significant differences were observed between eco and vivo measurements for CRL and BPD in all examined concepti. CRL and BPD, instead, showed a significant positive linear correlation with gestational age. The study of osteogenesis dynamics has demonstrated a completely cartilaginous ovine fetus at up to 35 days of gestation. The ossification begins in the skull (40th day) and is almost complete between the 65th and the 70th of pregnancy. Our study highlighted that CRL and BPD are accurate parameters for gestational age estimation in the first part of sheep pregnancy and provides an overview of osteochondral temporal dynamics. Furthermore, tibia ossification is a valid parameter to estimate fetal age by ultrasound.