Age associated morphological changes in the lymphoid system of tropical cattle.

Superficial (superficial cervical , subiliac) and deep (medial iliac) lymph nodes, tracheobronchial and mesenteric lymph nodes, Peyer's patches, thymus and spleen were collected from 165 apparently normal animals ranging from fetuses of six months gestational age to cows approximately 10 years old. Additionally, palatine tonsils were collected from 58 other animals of comparable ages. Weights of animals and most of the above organs were obtained and in 39 animals, representing seven age groups, quantitative histological studies were made on Peyer's patches or lymph nodes to ascertain any differences attributed to age or anatomical location of node. With the exception of thymus, weights of all lymphoid organs increased with age until puberty or maturity after which a levelling of organ weights was apparent. Organ weight-bodyweight ratios, however, were highest in fetuses or young animals after which they decreased (somewhat irregularly) with age. Few trends were observed relating histological findings to age. Depth of Peyer's patches and the follicular-non-follicular ratio (FNFR) in the cortices of superficial cervical plus subiliac nodes, however, increased rapidly (to approximately nine months and three years of age, respectively), reached a plateau, and then decreased. Pigment deposition in all nodes tended to increase with age. In regard to anatomical location, the medial iliac node (probably because of its deep location) tended to have the lowest corticomedullary ratio and FNFR, smallest germinal centre size and least pigment.