Identification of best temperature humidity index model for assessing impact of heat stress on milk constituent traits in Murrah buffaloes under subtropical climatic conditions of Northern India

Abstract

The present study was conducted to identify the most suitable temperature humidity index (THI) model among seven reported THI models for analyzing the impact of thermal stress on monthly test day fat % (MTDF%),monthly test day SNF% (MTSNF%), monthly test day fat yield (MTDFY) and monthly test day SNF yield (MTDSNFY) of Murrah buffaloes at subtropical climatic conditions of Karnal, India. A total of 8868 MTDF% and 8606 MTDSNF% records from 1107 lactational records of Murrah buffaloes under five parities were included in the present study and weather information on dry bulb temperature (Tdb), wet bulb temperature (Twb) and relative humidity (RH in %) for the corresponding period of 20 years (March 1994- December 2013) were collected from ICAR-NDRI and ICAR-CSSRI, Karnal, respectively. The overall least-squares means for MTDF% ranged from 7.71 ± 0.067 in TD1 to 8.10 ± 0.08 in TD 9 and MTDSNF% ranged from 9.61 ± 0.01 in TD5 and TD 6 to 9.65 ± 0.01 in TD 8. The overall least squares means of MTDFY (g) ranged from 411.23 ± 14.74 to 745.98 ± 13.57 while for MTDSNFY (g) the value ranged from 491.90 ± 17.21 to 922.16 ± 15.17. Monthly average THI was computed for each of the seven models. The lowest monthly average THI value was found in January, while either May, June or July showed the highest average THI value for all seven THI models. Regression analysis was performed for identifying the best THI to assess the impact of heat stress on milk constituent traits under study anda negative association was found between the milk constituent traits and monthly average THI values.The THI model[THI = (0.55 × Tdb + 0.2 × Tdp) × 1.8 + 32 + 17.5]developed by NRC(1971)was identified as the most suitable THI model to assess the impact of heat stress on milk composition traits of Murrah indicating maximum decline in MTDF% (-0.005), MTDFY (-0.68 g),MTDSNF% (b=-0.0008) and MTDSNFY (-2.25 g) per unit rise in THI.