Abstract
The present study examines the influence of the temperature-humidity index (THI) on some hematological parameters and leukocyte indexes in dairy cows during transitional (spring and autumn), summer and winter periods. It was ascertained that in the summer the hematopoiesis intensifies and as a result, the number of the erythrocytes of the animals from all three farms builds up by 7 – 8%, while during the transitional and winter periods their number remains almost unchanged. Similar increase is also observed with reference to the haemoglobin (10 – 15%) and the number of leukocytes (more than 6%). Unlike the season, the «farm» factor has a considerably weaker influence.
The leukocytes increase during the summer is not linked to any change in their groups. In most of the leukocyte groups the fluctuations are within the physiological norms. This gives grounds for assuming that despite the high THI during the summer, the immunological reactivity of the animals remains stable. Monocytes increase (6,5 – 10) is observed during the transitional period in the animals which are bred in open houses.
The blood cell coefficient (BCC) also marks its highest values during the summer (from 0,98 to 1,08), followed by the winter (0,83 – 0,93) and the transitional period (0,68 – 0,84). The lymphocyte- granulocyte index (LGI) as well as the neutrophils and lymphocytes ratio are to a large extent dependent on the season and the type of farm – P<0,001.
The lymphocyte granulocyte index (LGI) and the ratio between neutrophils and lymphocytes (NLI), lymphocyte/eosinophils (LEI), and neutrophils/ eosinophils (NEI) depend both on the season and the type of farm P<0,001. During the transitional period these indexes are 2-3 times higher only with reference to the animals bred in the open buildings.
The lymphocyte /eosinophils and neutrophils/ eosinophils indexes are almost equal both during the hot summer and cold winter periods.
Keywords: dairy cattle, heat stress, blood cell parameters and leukocyte indexes