Determination of heat stress zone for daily milk yield using carryover heat effect model in Murrah buffaloes

The objective of the present study was to determine heat stress zones (HSZ) in a year for daily milk yield (DMY) of Murrah buffaloes. Data for the study included 2,67,599 daily milk yield records of 445 Murrah buffaloes sired by 171 bulls as well as climatic parameters, viz. dry bulb temperature (T_db) and wet bulb (T_wb) temperatures spanning over 16 years (2001-2016). The regression analysis of DMY on carryover heat effect indicated that the decline in DMY was significant above the carryover heat effect (CHE) 70. April-November were critical for daily milk yield, and maximum decline in daily milk yield was observed during the month of August in Murrah buffaloes. Therefore, two zones in a year were classified as non-heat stress zone (NHSZ) with CHE < 70 for months December-March and heat stress zone (HSZ) with CHE > 70 during April-November.