Delineation of temperature-humidity index (THI) as indicator of heat stress in riverine buffaloes (Bubalus bubalis) of a sub-tropical Indian region.

The erstwhile developed temperature-humidity index (THI) has been popularly used to indicate heat stress in dairy cattle and often in buffaloes. However, scientific literature suggests differences in thermotolerance and physiological responses to heat stress between cattle and buffalo. Therefore, THI range used to indicate degree of heat stress (mild, moderate, and severe) in cattle should be recalibrated for indicating heat stress in buffaloes. The present study was carried out to delineate THI range to indicate onset and severity of heat stress in buffaloes based on physiological, biochemical, and expression profiling of heat shock response (HSR) genes in animals at different THI. The result indicated early onset of heat stress in buffaloes as compared to cattle. Physiological and biochemical parameters indicated onset of mild signs of heat stress in buffaloes at THI 68-69. Significant deviation in these parameters was again observed at THI range 73-76. At THI 77-80, the physiological and biochemical responses of animals were further intensified indicating extreme alteration in homeostasis. The in vivo expression profiling of HSR genes indicated that members of Hsp70 gene family are expressed in a temporal pattern over different THIs, whereas expressions of Hsf genes were evident during intense heat stress. Overall, the study established that amplitude of heat shock response and THI range for indicating severity of thermal stress for buffaloes are not in unison to cattle. The study also suggests skin temperature of the poll region could be used as non-invasive tool for monitoring heat stress in dairy buffaloes.

Reassessment of temperature-humidity index for measuring heat stress in crossbred dairy cattle of a sub-tropical region.

The temperature-humidity index (THI) has been extensively applied for assessing heat stress in moderate to hot conditions in dairy cattle. However, there exist wide variation between researchers in defining an appropriate range of THI values for denoting different levels of stress. The present study was aimed to reassess previously described heat stress indicators of dairy cattle of sub-tropical region of India. From comparative evaluation of meteorological data over previous four years (2014-2017) the period of year when high THI prevailed in the region was determined. Accordingly, the time period of sample collection and observation on animals was decided, so that a THI range of 68-86 could be covered. After analyzing physiological, biochemical parameters and expression profile of heat shock response (HSR) genes of animals in response to different THI, it was evident from the study that animal undergoes few or little changes at THI 72, but major physiological changes occurred after THI reached 74. At THI range 74-79, no drastic change in these parameters occurred suggesting animals undergo transient acclimatization in this range to maintain homeostasis. Once THI reached and crossed 80, this homeostasis was perturbed and animals experienced major physiological changes again. Overall, the study suggests that THI values indicating level of heat stress are dependent on the geographic location, as well as type of animal and therefore, existing THI should be recalibrated for different climatic region for accurate assessment of the heat stress.