Age-dependent changes of gut-associated lymphoid tissue in one to four-month-old turkeys: A histological study

Abstract

Gut-associated lymphoid tissue (GALT) has a pivotal role in the health of birds as the first line of defense against foodborne pathogens. On the other hand, this part of immune system is important for successful development of vaccines. Due to scarcity of knowledge on GALT of turkey as a major industrial species, this study aimed to evaluate histological features of GALT in this species. A total of 40 clinically healthy BUT6 turkeys from both sexes at the age of 1, 2, 3, and 4 months were included in the study. Samples were immediately removed after slaughter from different parts of the gut, including pharyngeal tonsil, cervical oesophagus, oesophageal tonsil, proventriculus, pyloric tonsil, ileum, Meckel’s diverticulum, caecal tonsil, the middle and apex of caecum, rectum, and cloaca. After fixation and routine procedures followed by hematoxylin-eosin staining, samples were studied histologically under light microscope. In addition, photomicrographs were taken from sections and were analysed for histomorphometric parameters using Zeiss Axio vision rel.4.8 software. According to the results, in one-month-old turkeys, lymphatic tissues in pharyngeal tonsil, pyloric tonsil, proventriculus, caecal tonsil, middle, and apex of caecum, Meckel’s diverticulum, and cloaca were completely developed, while in some other parts such as the cervical oesophagus and the rectum lymphatic structures were absent. In the ileum, the Peyer’s patch was observed as an aggregated structure, although the diffuse lymphatic tissue has properly evolved. In two months old turkeys, the dense lymphatic tissue including primary and secondary lymphatic follicles, was present in cervical oesophagus, Peyer’s patch, rectum, and cloaca. Many histomorphometric parameters of lymphoid tissue also developed age-dependently. In four months old birds the dense lymphatic tissue was obvious in all examined specimens. Moreover, no signs of tissue atrophy were seen at the age of four months (prepuberty) in the GALT specimens. In conclusion, the GALT of turkeys was histologically quite similar to those of other birds and these structures showed an age-dependent development from 1 to 4 months of age.