Impact of temperature humidity index (THI) on physiological responses and milk yield of Tharparkar and Karan Fries cows exposed to controlled environment

Tharparkar and Karan Fries cows were exposed to 25 degrees C, 35 degrees C and 42 degrees C with relative humidity of 5015%, 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 (degrees 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 degrees C in Tharparkar and 7.45 to 8.42 degrees 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.