Novel heat index models for subtropical region based on daily milk production in crossbred Holstein cows


Abstract: The quantification of the effect of heat stress imposed due to higher rate of heat gain on animal production is a prerequisite while estimating effects of heat stress. Temperature humidity index (THI) models developed empirically using meteorological parameters have been utilized as an indicator of heat stress. This study attempted to develop a heat index model with respect to productivity of the crossbred Holstein cows. More than 1.23 million daily milk yield records of 1860 crossbred cattle spread over a duration of 30 years were utilized. Statistically significant (p < 0.0001) partial regression coefficients were estimated as 0.0748 ± 0.0009 for dry bulb temperature (T$_{db}$) and -0.2228 ± 0.0011 for wet bulb temperature in model 1, -0.0182 ± 0.0005 T$_{db}$ and -0.1205 ± 0.0006 for vapour pressure in model 2, -0.0150 ± 0.0006 for Tdb and -0.1151 ± 0.0006 for dew point temperature in model 3 while as -0.1283 ± 0.0004 for T$_{db}$ and -0.0394 ± 0.0002 for relative humidity in model 4. The ratio of the partial regression coefficients of meteorological parameters (ß2/ß1) was -2.9791 in model 1, 6.8739 in model 2, 7.6731 in model 3 and 0.3073 in model 4. The developed THI models are based on the effect of meteorological parameters on daily productivity of the dairy animals, so the weightages to meteorological parameters were contrastingly different than the reported THI models. These models may successfully be used to evaluate the impact of heat stress on crossbred Holstein cows with respect to milk productivity and many other traits.

Keywords: Temperature humidity index, cattle, heat stress, daily milk yield

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