Abstract
Tharparkar and Karan Fries cows were exposed to 25°C, 35°C and 42°C with relative humidity of 50±5%, corresponding to THI of 72.2, 85.3 and 91.0, respectively for three hours continuously for three days consecutively in the control climatic chamber. At THI of 91.0, physiological responses i.e. RR/ min, PR/min and RT (°F) increased by 14, 13, and 1.18 in Tharparkar and 23, 14 and 2.98 in Karan Fries cows, respectively over pre exposure values. At THI of 91.0, the surface body temperature was increased over THI 72.2 by 5.21 to 7.52°C in Tharparkar and 7.45 to 8.42°C in Karan Fries cows. Skin blood flow of Karan Fries cows was increased by 4.98, 4.15 and 3.95 PU at THI 85.3 and 6.84, 9.18 and 8.04 PU at 91 THI over the pre exposure values of respective THI at dorsal, ventral and ear part of body, respectively. The decrease in milk yield was calculated in the THI range of 72.2 - 91.0, the milk yield was decrease (per unit increase in THI) by 135.11ml in Karan Fries and 51.60 ml in Tharparkar cows. The results of the study clearly indicated the more sensitivity of Karan Fries compared to Tharparkar cows at higher THI. Therefore, Karan Fries cows needs protection from extreme heat for sustained production performance.
Highlights
In India, livestock plays a crucial role in the socioeconomic development and is the major source of livelihood
The magnitude of increase in respective physiological parameters over pre exposure values was further higher after three hours of exposure at THI (91) i.e. 14, 14, and 1.18 in Tharparkar and 23, 14 and 2.98 in Karan Fries cows (Table 1)
The results of present study is in accordance with those of Velagala and Singh (2018) who reported significantly higher physiological responses during hot humid season and in Karan Fries cattle compared to autumn and Tharparkar cattle respectively during exposure under natural ambient conditions
Summary
In India, livestock plays a crucial role in the socioeconomic development and is the major source of livelihood. The major limitation to livestock production system in tropical countries including India is heat stress/ climate change. Sahiwal and cross-breed, Frieswal were found to have different heat stress responses in-terms of body rectal temperature, respiration rates and production parameters under stress conditions (Sajjanar et al, 2015). Quantitative measures of the thermal environment and the animals' responses to heat stress are needed to assess thermal tolerance. Used measures of the thermal environment are temperature, humidity, solar radiation, and wind speed, whereas coat characteristics, core body temperature, skin temperature, respiration rate, and sweating rate describe thermal environment from an animal perspective. Keeping in view the above facts in mind, present study was designed to compare the heat tolerance of indigenous (Tharparkar) and crossbred (Tharparkar x Holstein Friesian) cattle under different temperature humidity indices in the controlled climatic chamber
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