Effect of THI on Milk Production and Physiological Responses of Crossbred Cows During Different Months Under the Agro Climatic Condition of Bihar

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Ten crossbred (Holstein Friesian x Indigenous Local) lactating cows of first lactation were maintained in semi open RCC housing system with concrete floor and GI sheet roof at institute farm. Multiple regression analysis revealed that air temperature, effective temperature , temperature humidity index (THI) had significant (P<0.01) effect on average daily milk yield/ cow (Kg), average weekly milk yield / cow (Kg), average monthly milk yield / cow (Kg) and daily total milk yield of cows (Kg). Average daily milk yield / cow (Kg), average weekly milk yield / cow (Kg), average monthly milk yield / cow (Kg), daily total milk yield of cows (Kg) were reduced by 0.886, 1.868, 2.471 and 4.375 kg respectively per unit increase of temperature humidity index. Data analysis revealed that different months had highly significant (P<0.01) effect on all the cardinal physiological reactions i.e. rectal temperature, respiration rate and pulse rate in growing calves during different months. It was also observed that rectal temperature increased significantly (P < 0.05) by 0.13, 0.01 and 0.25 0 C with the unit increase of air temperature, relative humidity and THI. Similarly respiration rate was increased significantly (P<0.05) by 2.48, 0.48 and 8.62 / minute with the unit increase of air temperature, relative humidity and THI. Both Iberia Heat Tolerance Coefficient and Benezara coefficient of adaptability indicated highest thermo adaptability of crossbred calves in the month December.