Effect of temperature-humidity index on physiological and haematological indicators in dairy cows

Abstract

Heat stress in cows is commonly assessed using the temperature and humidity index (THI), a combination of ambient temperature and relative humidity. In this study, the influence of the THI on haematological and other physiological indicators in cows was evaluated. A significant difference was found in respiratory rate; when THI increased above 70 breaths/min, respiratory rate increased from 19.8 to 34.4 breaths/min. When THI increased above 80 breaths/min, there was a sharp increase in respiratory rate to 128.8 breaths/min. This was observed between 3 and 4 clocks in the afternoon when the highest thermal stress was assumed in dairy cows. The correlation coefficient between THI and body temperature was 0.38, but when weighted averages of minimum temperatures for three days were used, the correlation coefficient increased to 0.48. Based on these results, it is more reasonable to use the minimum THI over several days. At critical temperatures, haemoglobin decreased to 115.45 ± 23.12 g/l, compared with values measured in dairy cows under optimal conditions. However, these values did not fall below 125 g/l. A similar trend was observed for hematocrit under optimal conditions it was 34.42 ± 1.03%, and under stress, it was 37.5-39.12%. The number of erythrocytes was the lowest (6.51 ± 0.137 × 1012/l) in the most heat-stressed dairy cow group.

Keywords

• dairy cows
• heat stress
• temperature-humidity index
• body temperature respiratory rate
• haematological indicators