Abstract
This article shows the research findings on age-related changes in the extramural glands of the digestive system of sheep during the postembryonic stage of ontogenesis. The study identified the first month as the most critical period in the postnatal ontogenesis for the growth and development of extramural digestive glands, marked by the most intensive growth in relative organ masses (liver and pancreas of sheep from 12 to 15 months). Organ growth is sustained for 2-3 months, followed by a decline in the growth rate and maximum parenchymal development. Changes in the relative mass of the liver and its lobes occur non-uniformly in terms of the aging process. The relative mass values of the liver lobes increase most intensively up to the age of 12 months, after which they gradually decrease. The weight of the pancreas increased 14.84 times from the age of 3 days to 48 months. The most intensive linear growth occurs at the ages of 3 and 12 months of postnatal development, with the growth values of the right lobe exceeding those of the left lobe and the body of the gland. The histological structure of the liver and pancreas has a typical organization. The development processes of glandular epithelium in the extramural digestive glands occur unevenly and exhibit heterochrony, manifested in the establishment of their structural organization.