Determination of critical heat stress zone for fertility traits using temperature humidity index in Murrah buffaloes

The objective of the present study was to determine critical heat stress zone (CHSZ) in a year for fertility traits of Murrah buffaloes like service period (SP), pregnancy rate (PR) and conception rate (CR). Fertility data on 1,379 lactations and climatic parameters, viz. dry bulb temperature (Tdb) and relative humidity (RH) spanned over 20 years (1993–2012) were collected from NDRI and CSSRI, Karnal. The regression analysis indicated that the maximum increase in SP and maximum decline in PR and CR with per unit increase in THI value. Two zones in a year were classified as non-heat stress zone (NHSZ) with THI 75 during April to September. SP increased by 8 and 19 days under NHSZ (56.71 - 73.21) and HSZ (75.39 - 81.60), while there was maximum increase in 28 days service period in May and June with per unit rise in monthly average THI value. A negative association between THI and PR, CR were also observed under NHSZ and HSZ. However, maximum decline in PR (7%) was found for May and June while June, July and August showed the highest depression in CR at 9 % with per unit increase in THI. Therefore, May and June were determined as CHSZ for SP and PR, whereas June, July and August as CHSZ for CR in Murrah buffaloes with THI 80.27 - 81.60.