The results of morphological examination of blood of cows under heat stress depending on the stages of temperature-humidity index

The results of morphological studies of the blood of cows under heat stress indicate that the temperature - humidity index (THI) of animals in comfortable conditions (THI - 68-71) the number of erythrocytes is 5.78 ± 0.13 T / l, the hematocrit - 24.98 ± 1.02%, hemoglobin content - 89.96 ± 2.63 g / l, MCV - 39.76 ± 2.31 fl; MCH - 15.56 ± 1.32 pg; MCHC - 39.14 ± 1.95 g / dl. The total number of leukocytes in the blood of cows is 7.17 ± 0.54 G / l. The relative content (leukogram) and the absolute number of certain types of leukocytes in the blood of cows has no abnormalities. This suggests that the morphological parameters of the blood of cows in the comfortable conditions of THI meet the normative values for cattle and, in particular, Holstein breed. Under moderate heat stress (THI -72-78), in the blood of cows, along with a significant increase in respiratory rate and heart rate, there is a tendency to increase the number of erythrocytes to 5.82 ± 0.69 T / l, there is a significant increase in hematocrit and MCV by 20 and 47%, and a significant decrease in hemoglobin, MCH and MCHC - by 32, 35 and 55%, respectively, relative to control. However, in the blood of cows there is a tendency to decrease the number of leukocytes, with the simultaneous appearance of metamyelocytes, an increase in the number of eosinophils and rod neutrophils, and a significant decrease in the number of lymphocytes by 27% compared to control. Under severe heat stress (THI - 80-90), when the pulse in cows fluctuates between 88-140 beats per minute, and the respiratory rate is 82.0 ± 3.76 respiratory movements, the number of erythrocytes in the blood of cows tends to decrease and is 5.01 ± 0.91 T / l. The hematocrit value is 21% significantly (p≤0.05) less than in cows under moderate heat stress, and is almost the same as in cows under comfortable conditions. The content of hemoglobin in the blood of cows in this period is significantly lower by 28% (p≤0.05) compared to that in cows under comfortable conditions with a slight tendency to increase compared to this figure in cows under moderate heat stress. Color indices indicate that in the blood of cows under severe heat stress there is a large number of young erythrocytes-macrocytes (MCV - 53.69 ± 3.22 fl), which are poor in hemoglobin (MSN - 12.95 ± 3.48 pg) and impaired hemoglobin formation (MCHC - 24.11 ± 2.23 g / dl). The total number of leukocytes in the blood of cows under severe heat stress is 10.80 ± 1.55 G / l, which is 78% (P≤0.01) more than under moderate heat stress and increases due to the appearance of young and an increase of almost in twice rod-shaped and segment-nuclear neutrophils and eosinophils with a simultaneous decrease in the percentage of lymphocytes.