Sustainability in livestock production system is largely affected by climate change. An imbalance between metabolic heat production inside the animal body and its dissipation to the surroundings results to heat stress (HS) under high air temperature and humid climates. The foremost reaction of animals under thermal weather is increases in respiration rate, rectal temperature and heart rate. It directly affect feed intake thereby, reduces growth rate, milk yield, reproductive performance, and even death in extreme cases. Dairy breeds are typically more sensitive to HS than meat breeds, and higher producing animals are, furthermore, susceptible since they generates more metabolic heat. HS suppresses the immune and endocrine system thereby enhances susceptibility of an animal to various diseases. Hence, sustainable dairy farming remains a vast challenge in these changing climatic conditions globally.

Expression of stress genes under thermal stress partially explain the relatively higher thermal adaptability of indigenous breeds compared to exotic breeds of cattle. ATP1A1 gene is one of such gene that encodes for a1 isomer of Na+, K+- ATPase enzyme for Na+- coupled transport of metabolites, nutrients, ions and represents a plausible candidate for heat tolerance traits. Present study was designed to compare SNP variations in ATP1A1 gene and to evaluate their association with respiration rate, rectal temperature and heat tolerance coefficient in Sahiwal (51) and Karan Fries (50) cows maintained at Livestock Research Centre of National Dairy Research Institute, Karnal. Two SNPs (T27008243C and A27008223G) were identified in both the dairy cattle breeds. Association of each SNP genotype was analyzed using Generalized Linear Model procedure in Statistical Analysis System (SAS). Sahiwal cows with TT (15.91±1.89b) at T27008243C locus had lowest RR compared to TC genotypes (18.25±1.77ab) and CC genotype (19.24±1.52a), while in Karan Fries cows RR for AA genotype at A27008223G locus was lower (28.85±1.96b) compared to GG genotype (32.37±2.51a). Thus, the study indicated that the TT genotype at T27008243C locus in Sahiwal and AA genotype at 27008223 locus in Karan Fries cows are desirable genotypes for genetic adaptability under heat stress.

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