Histomorphometrical study of notochord in the water buffalo embryos of Khozestan, Iran

    The notochord is a flexible and rod-shape structure that is typical characteristic of vertebrates and replaced mainly by intervertebral disc in mammals. Finally, the notochord disappears depend on animal species and take part in formation of intervertebral disc and nucleus pulposus. There is no report about the development of notochord in the water buffalo. This study was performed on 20 water buffalo embryos with CRL from 3.8 to 38 mm and estimated age from less than 30 days to 54.28 days. According to histological and developmental changes the embryos divided in 3 groups: group 1(8 embryos, CRL= 7.06± 0.16 mm, estimated age= less than one month), group 2 (5 embryos, CRL=14.5± 0.15 mm, estimated age= 35.38 ± 1.34 days) and group 3(7 embryos, CRL=28.5±0.75 mm, estimated age=51.64 ± 4.29 days). For histological purposes 0.5 cm from lumbar part of the vertebral column was sectioned transversally fixed in 10% formalin and serial sections prepared at 5 - 6 µm thickness. The sections stained by H& E and studied by light microscope. The results showed that maximum development and regression of the fetal notochord was occurred on embryos with CRL= 8.9 mm and 38 mm (less than one month old and 55 days), respectively. The notochord consists mainly of mesenchymal cells with round nucleolus, clear nucleolus and light cytoplasm. However, with increasing age of embryo, the number of notochordal cells gradually decreased and finally disappeared. At the end of embryonic period, the notochord structure changed and limited to small round area with thick wall that was without any cells in the center of the intervertebral disc named nucleus pulposus. Additionally, our finding showed that formation and subsequent regression of notochord is very similar with reports about notochord of cattle. On the basis of literature, the maximum development and growth of notochord is on 40-50 days in human. However, our results revealed that the regression of the notochord in water buffalo embryos occurred with 51.64 ± 4.29 days old. So, it is concluded that regression of the notochord and formation of intervertebral disc in the water buffalo embryos is very similar with other domestic animals and especially cattle.