Abstract The Harderian gland of 110 laying hens was histologically investigated from the time of hatching to the period of 10 months of age. Tissue sections were stained with haematoxylin and eosin, periodic acid-schiff (PAS) and methyl green-pyronin technique. The research shows that lymphoid tissue is colonised by three types of cells: heterophils, lymphocytes and plasma cells. The number of these cells is directly dependent on the bird’s age. During the lifetime of the hens there gradually comes a shift in the dominance of these three cell types. Lymphoid nodules are detected only in 40-day-old chickens, while later in adult birds the Harderian gland is the organ which contains the largest number of mature plasma cells. Some plasma cells contain Russell bodies with different size and shape.

Lameness in sheep, especially in semi-extensive breeding of Dubska pramenka, which starts in the interdigital region, was the motive of our morphological and histological research, in order to and in some way, bring the structure of the interdigital sinus in correlation with the appearance of this pathological state that causes extensive economical losses in the domestic sheep breeding,. The anatomical location of the interdigital diverticulum, its histological structure, which point to abundance of sebaceous glands around the hair follicles surrounding the interdigital opening and interdigital glands in deeper layers, point to the suggestion that their secretion increases due to poor hygienic keeping conditions. Pathogens - anaerobic microorganisms, which are most commonly causing the contagious lameness find the ideal conditions for their growth and reproduction because the secretion of these glands is likely "to close" the only "air" communication - interdigital opening.