The fine structure of broiler chicken blood cells, with particular reference to basophils, after severe heat stress

Abstract

The fine structure of blood cells, with particular reference to basophils, was studied in broiler chickens before and after they had been subjected to heat stress. Granule counts in basophils after heat treatment showed a significant reduction in their total numbers compared with pre-heat treatment. This depletion of granules corresponded with evidence of degranulation seen at the ultrastructural level. Of the three types of basophilic granules described, only the type I electron-dense, homogeneous variety of granule was significantly reduced in number. After heat stress, there was a significant increase in heterophil lobulation. In several birds there was also evidence of cytoplasmic fragmentation in the form of portions of cells containing granules but no nuclei, lying free in the circulation. Damaged mitochondria, not seen before heat treatment, were frequently observed in the cells. Monocytes also showed significant increases in cytoplasmic lipid droplets after heat stress compared with pre-heat treatment, suggesting the onset of possibly early fatty degeneration. However, there was no evidence of increased pseudopodia or pinocytotic activity in these cells. With heat stress, there was a significant reduction in the numbers of electron-dense granules in the small lymphocytes. Despite there being a smaller proportion of circulating eosinophils after heat stress, which was considered to be the result of an immediate stress response, no significant differences were evident between pre- and post-heat treatment in the cells. The red cells and thrombocytes from post-heat-stressed broilers were significantly longer and thinner compared with pre-heat treatment due possibly to dehydration. The dimensional and ultrastructural changes identified in the cells after heat stress question their effective functional ability in raising an immune response under such circumstances.