Vijayan, NSuraj, SKAU2019-05-282019-05-282002172007http://krishikosh.egranth.ac.in/handle/1/5810105058PGThe experiment was designed to study the pathology of induced stress in broiler chicken and to identify suitable markers for recognition of stress. One hundred and two, day old broiler chicks were divided into three groups of 34 birds each. Birds of Group I was administered dexamethasone orally at the rate of 50 ppm on the 20th day followed by 25 ppm on days 27, 34, 41 and 44. Group II was stocked at higher density of 0.25 if/bird till 28th day and then at 0.5 felbird, while Group III served as control. Behavioural changes, production parameters, haemogram, immunological parameters, and pathological changes in the organs were recorded to study the pathology and to identify suitable markers of stress. Birds of Group I were depressed and developed mild infection while \ Group II showed poor feather development and hyper responsiveness to stimuli initially followed by depression and lameness. Birds of Group I and II showed lower body weights and feed efficiency except for Group II• on the 21st day when higher body weights and better feed efficiency was observed. Leukocytosis, lower values for RBC, haemoglobin and VPRC along with heterophilia, lymphopenia and higher heterophil to lymphocyte ratio were t- recorded for both the stressed groups. Basophilia was observed towards the end . of the experiment in Group II. Birds of Group I showed increased tendency to deposit abdominal fat along with wasting of muscles while in Group II bruises as well as scratches in breast muscles and pododermatitis were prominent lesions observed. The mean weights of the adrenal was lower in Group I however the mean adrenal weight to body weight ratios were higher. Both mean and relative mean adrenal weights were higher for Group II. The mean weights and organ weights to body weight ratio of bursa, thymus, and spleen were lower for both the stressed groups. Mean liver weight and liver weight to body weight ratio were higher for both the stressed groups. Adrenals from Group I showed increased proportion of epinephrine producing medullary cells on the 21 st day but on 28th day the numbers, of cortical cells had increased. During the latter stages of the experiment the cortical and medullary cells were seen in various stages of degeneration and necrosis. In Group II hypertrophy and hyperplasia of the cortical and medullary cells which were organised into spherical clusters along with aggregation of cortical cells in the. periphery were seen during the initial 'half of the experiment. Towards the latter stages the cell clusters showed tendency for cyst formation. Bursa from Group I showed degeneration and necrosis of the follicles along with mucosal hyperplasia and cyst formation. In Group II bursal intra follicular and inter follicular oedema followed by degeneration of the lymphocytes were observed. Thymus and spleen showed lymphoid depletion in both the treatment groups. Liver and kidneys of both the stressed groups showed degenerative and necrotic changes. The intensity of pathological lesions were more in Group I than in Group H. Stress scores were found to be good marker for identification of stress and can serve as a useful tool to identify suitable markers for stress. The results of the present study highlights the adverse effects of stress on the immunobiological response. The correlation between the changes in the adrenal and the immunological organs were delineated. It would be better to use a battery of tests like behavioural alterations, haemogram, production indices together with gross and microscopic changes in the various organs for assessing stress response. Stress scores was identified as a useful marker and tool to identify markers of stress. Van Gieson's fast green and phosphotungstic acid haemotoxylin staining methods were identified as suitable staining methods for differentiating adrenal, cortical and medullary cellsennullThesis