author(s)
P Mayengbam, RC Upadhyay and TC Tolenkhomba

abstract
A study was carried out to find out the effect of temperature humidity index on the neutrophils lymphocyte ratio of Sahiwal heifers in five different periods. The five different temperature conditions maximum ambient temperature/minimum ambient temperature (Tmax/Tmin) were P1: <20 ^oC/<10 ^oC; P2: >20 ^oC/<10 ^oC, P3: >25 ^oC/<15 ^oC; P4: >35 ^oC/<20 ^oC and P5: >35 ^oC/>20 ^oC. The study further investigated the effect of acute thermal exposure on neutrophil lymphocyte ratio of Sahiwal heifers. Exposure was done at two intervals viz. Exposure I at 40 ^oC and 50%RH and Exposure II at 45 ^oC and 50% RH. Thermal exposure was done in the climatic chamber for 4 consecutive hours. Neutrophil leukocyte ratio was calculated from differential leukocyte count of blood smears stained with Leishman’s stain. Neutrophil lymphocyte ratio of Sahiwal was found to be stable throughout the year in natural climatic conditions. Exposure at at 40 ^oC and 50%RH in climatic chamber caused a significant increase in the neutrophil lymphocyte ratio of Sahiwal. The study revealed good thermotolerance of Sahiwal cattle in natural climatic conditions. In response to acute thermal stress Sahiwal heifers showed an increase in neutrophil lymphocyte ratio. The study indicated neutrophil lymphocyte ratio to be a heat stress marker.