Dynamics of lymph nodes weight characteristics in cattle during the prenatal period of their ontogenesis

In lymph nodes, as peripheral organs of the immune system, the patterns of their growth and development are unique in many ways, especially during the prenatal period of ontogenesis. The changes in the absolute and relative mass of lymph nodes in 66 bovine fetuses of different gestational ages (2–9 months) were studied. The weight of the fetuses and organs was determined with an accuracy of 0.001 g. According to the indicators of weight, body length, and the degree of development of the fetal skin derivatives, their age was established. It was found that in the first third of the fetal period of ontogenesis, the dynamics of the lymph nodes’ absolute mass was characterized by a moderate increase, which occurred simultaneously with an increase in the weight of the fetus itself. The relative weight at the beginning of the fetal period changed unevenly: it decreased in the superficial cervical and mandibular and increased in the popliteal and caudal mediastinal lymph nodes. In the second third of the fetal period, both the absolute and the relative weight of the examined organs increased dramatically (with the maximum at 7 months-old age). During the last third of the fetal period, a gradual increase in the absolute mass of all lymph nodes was found, and their relative mass, on the contrary, decreased moderately. In the second and last third of prenatal development, there was no direct relationship between the growth of the lymph nodes mass and the fetal total mass.