In the paper, we consider the morphology of intestine structures and gut-associated lymphoid tissue of meat rabbits. The investigation was carried out for the rabbits of the following ages: 1, 10, 20, 30, 60 and 90 days of postnatal development. In accordance with the age groups, the samples of small and large intestines were taken and stained with hematoxylin eosin. As the result of microscopy investigations, the morphology of intestines and lymphoid tissues was studied. We found out that the most area of a microscopic section was taken up by mucosa, whereas lymphoid cells were detected mainly in lamina propria and somewhat in epithelium. We observed that immune structures of 30-day rabbits were formed in lamina propria hardly breaking the submucous layer. For the 1-day rabbits, the lymphoid tissue was detected in sacculus rotundus and vermiform appendix. Starting from the 20-th day of postnatal development, the lymphoid tissue was also observed in lamina propria and other intestinal tracts. We found specific types of lymphoid tissue and immune structures, which were typical of each age group of the rabbits. Besides, we studied the traits of lymphatic nodule development within the selected ages as well as assessing differentiation periods of lymphoid tissue. We determined that lymphoid tissue could be detected for the newborn rabbits, viz. lymphatic nodules and aggregated lymphoid nodules (Peyer's patches) begin growing from the 20-th day of postnatal development, whereas germinal centers are observed in lymphatic nodules of 60-day rabbits. With age, the number of lymphatic nodules is increasing in lymphoid plaques whereas the amount of lymphoid tissue is decreasing between the plaques. Since birth, lymphatic nodules are mostly circular-shaped. However, irregular-shaped lymphatic nodules, which are arranged in two rows, are appearing in the lymphoid plaques starting from 30-day age. On the 90th day of postnatal development, almost all lymphatic nodules within the lymphoid paques have irregular shape and may be arranged in three rows. A well-developed bloodstream vessel cab be observed in the proximity of the lymphoid tissue and lymphoid structures of each rabbit age group.

Nowadays, new breeds of rabbits are appearing with high productivity and rapid growth rate. These breeds require fresh research to be conducted in different fields, which include morphology of the intestine and gut-associated lymphoid tissue (GALT). The morphology of the intestine and GALT of meat rabbits are the investigated objects of the current research. We conducted the investigation on rabbits of different ages (1, 10, 20, 30, 60 and 90 days old). Each age group consisted of five animals. All veterinary ethical requirements were complied with. The body lengths and body masses were measured. Using t-coefficients, we estimated the range of variation of these parameters in each age group. The conclusion about this variation was taken. The masses and lengths of the different intestine parts were investigated as well. Using the obtained values, we provided a continuous numerical model to compute the mass and length of any intestine part of a rabbit of any age in the range from one to 90 days. This allowed us to represent the obtained empirical model by a plot for subsequent detailed study. We found that the changes in masses and lengths do not follow the same pattern for all intestine parts. For some intestine parts, this pattern is approximately linear in the range from one to 90 days; meanwhile for others, the changes in masses and lengths are quite complicated. We observed two local maximas of the growth rate for some intestine parts. Apart from the masses and lengths of the intestine parts, we accomplished macro analysis of the aggregated lymphoid nodules of each age group of animals. We estimated the index of gross area and the law by which it changes in each group. The research results presented here may be used as a basis for composing food ration, assessment of immune status and development of effective prevention and treatment against some diseases.

A feature of rabbit gut-associated lymphoid tissue is that its structure is more developed than in other animal species. In rabbits it is composed of sacculus rotundus, vermiform appendix and Peyer’s patches. These immune formations contain an organized component of lymphoid tissue – lymphoid nodules (B-cell zone) and interfollicular region (T-cell). Secondary lymphoid nodules with germinal centers presented in them are formed due to antigen stimulation. The caecum of Hyplus rabbits at the age of 30 -, 60 - and 90-days was investigated. Each age group consisted of 5 rabbits. Experimental rabbits are clinically healthy, unvaccinated and untreated against ecto- and endoparasites. Peyer’s patches of the caecum were selected for the study and fixed in 10% of formalin. Subsequently, the specimens stained with hematoxylin-eosin were prepared from the obtained samples. On the 30th day of life, Peyer’s patches in the cecum were detected by gross examination. On the histological level, they had formed interfollicular region and lymphoid nodules. In turn, lymphoid nodules were divided into primary and secondary ones. A well-defined mantle zone and germinal centers were observed in the secondary lymphoid nodules. The regularities of their area indicators increase (mean value, median and interquartile range (IQR)) and their correlation were studied. The most intensive growth of the mantle area and the germinal center was observed from the 30th to the 60th day. The relative area of the mantle zone and the germinal center as part of the secondary lymphoid nodule was determined. Its value did not change during the experimental period.

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.

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