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Present study was envisaged to examine existence of genetic group x THI in crossbred cows at institute herd of ERS, ICAR-NDRI, Kalyani, West Bengal. 1041 fertility records each on service period (SP) and conception rate (CR) and weather parameters spanned over 22 years (1994-2015) were collected; arranged under three THI groups; thermal comfort (THI<72), two heat stress zones (THI 72-78) and THI>78 and six genetic groups.SP was longest (163.61 ± 6.83 days) when THI>78and lowest (149.27±6.69 days) during THI<72. CR was lowest (65.66±2.73 %) when THI>78 and highest (70.54±2.8 %) at THI<72. Genetic group x THI was non-significant on SP and CR. However, there was re-ranking of genetic groups across three THI zones. Genetic group bearing 50% Jersey + 50% Tharparkar followed by 50% Jersey + 50% Red Sindhi exhibited least increase in SP (5.09 and 6.37 days) when THI>78.Cows bearing 50% Jersey and 50% indigenous cattle inheritance followed by 50% Jersey + 50% Red Sindhi and 50% Jersey + 50% Tharparkar depicted least drop in CR at THI>78 (-2.38, -2.40 and -3.6%) in comparison to THI<72. The genetic group with>75% Jersey depicted maximum increase in SP (15.33 days) and drop in CR (-7.43%) at THI>78. [ABSTRACT FROM AUTHOR]