Morphogenesis of endochondral ossification centres of bones in racing pigeon chicks during the early postnatal period of ontogenesis

Racing pigeons are potential carriers of zooanthroponic diseases, since they can travel considerable distances during their flight. The study of the formation features of the pigeon skeleton’s hematopoietic function on different levels of its structural organization with the determination of the relationship between the growth and development of hematopoietic components and the processes of osteohistogenesis is necessary to understand the immunity of pigeons, especially during the early stages of their development when young animals are in the greatest risk of disease, especially during processes of osteogenesis and haematopoiesis in chicks. The bones of the axial and peripheral skeleton of one-day-old, 5-, 10-, 15-, 20-, and 25-day-old pigeons (n = 5) were examined. The presence and degree of development of dia- and epiphyseal ossification centers (EOCs), their relative area (RA) and X-ray density in the organs of universal hematopoiesis were determined on radiographs made on an x-Ray-TW-102 x-ray machine with an Alpha 4600 receiver using the MultiVox Dicom Viewer program. It was established that in day-old pigeons the rudiments of the studied bones are completely built by cartilaginous tissue, have low radiographic density, and fuzzy contours on radiographs. On the 10th day of life, the axial skeleton of pigeon cubs has formed EOCs of head and a tubercle on the 5th rib (third «true rib»), while in the bones of the peripheral skeleton there is an enchondral EOC of the diaphysis. The spongy and compact bone structure (BS) of the bones were fuzzy. The body of the rib and the epiphyses of the limbs’ tubular bones were cartilaginous. The X-ray density of the humerus at this age remains unchanged, and the tibial-metatarsal increases by 1.5 times, reaching 12 HU. In 15-day-old chicks, the RA of the EOC in the skeleton was moderately increased due to an increase in the RA of previously formed EOCs at the age of 10 days, the appearance of individual EOCs in the body of 5th rib, and in the tubular bones of the limbs, the enchondral EOCs of the proximal and distal epiphyses. In the diaphysis of the extremities tubular bones, a strip-like compact BS was clearly distinguished, and in the epiphyses, a small-sized spongy BS. The X-ray density of the bones almost doubled, reaching 19–21 HU. In 20-day-old pigeons, the processes of osteohistogenesis in the skeleton were almost completed, in the studied bones, all the main and additional EOCs were well expressed, their RA increased sharply. X-ray density of bones did not change. For 25-day-old pigeons in the skeleton, there was a slight increase in RA of the EOC, a process of complete synostosis of the bones was characteristic. From the moment of the appearance of the EOC in 10-day-old chicks until they reach the age of 25 days, the bones of the axial skeleton and the skeleton of the limbs were formed by 95–100% of BS, and their X-ray density was increased almost 2.5 times, reaching 19–26 HU.