Assessment of expected breeding value for milk production traits of Murrah buffaloes under different heat stress zones in Indian sub-tropical climatic conditions.

Present study was conducted to investigate the impact of temperature humidity index (THI) on expected breeding value (EBV) for daily milk yield (DMY) and monthly test day fat% (MTDF%) and monthly test day SNF% (MTDSNF%) of Murrah buffaloes at ICAR-National Dairy Research Institute, Karnal. 302,101 records of DMY and 9864 records each on MTDF% and MTDSNF% buffaloes spanned over 20 years (1994 to 2013) from NDRI, Karnal, and meteorological were collected from ICAR-CSSRI, Karnal. The year was classified into three zones: non-heat stress (NHSZ), heat stress (HSZ), and critical heat stress zone (CHSZ) based on THI. The heritability (h) estimates for DMY, MTDF%, and MTDSNF% in NHSZ were 0.432 ± 0.054, 0.090 ± 0.004, and 0.070 ± 0.002; in HSZ 0.491 ± 0.073, 0.112 ± 0.003, and 0.052 ± 0.001; and in CHSZ 0.524 ± 0.077, 0.116 ± 0.004, and 0.092 ± 0.003, respectively. The repeatability (r) for DMY, MTDF%, and MTDSNF% in NHSZ were 0.528 ± 0.006, 0.166 ± 0.007, and 0.135 ± 0.007; in HSZ 0.572 ± 0.007, 0.198 ± 0.006, and 0.077 ± 0.006; and in CHSZ 0.599 ± 0.008, 0.217 ± 0.004, and 0.156 ± 0.009, respectively. EBV for DMY and MTDF% was maximum in NHSZ (8.85 kg and 7.85%) and in HSZ (7.27 kg and7.78%) and lowest (6.90 kg and 7.77%) at CHSZ. For MTDSNF%, EBV was highest during NHSZ (9.6403), declined to 9.6265 at HSZ, and marginally elevated to 9.6271 at CHSZ. Impact of climatic factors on milk production and constituent traits is vital, and proper management should be followed during the heat stress and critical heat stress periods to improve the production performance of Murrah buffaloes.