Indian Journal of Animal Sciences 94 (4): 333–341, April 2024/Article https://doi.org/10.56093/ijans.v94i4.132953 Modulations in antioxidant defence system and expression of genes involved in antioxidant and apoptosis pathway helps ward-off heat stress in cows reared in hot-arid ambience of Thar desert GAYATRI GUJAR 1 , VIJAY KUMAR 1 , MONIKA SODHI 2 , PRINCE VIVEK 2 , MANISH TIWARI 2 and MANISHI MUKESH 2* Rajasthan University of Veterinary and Animal Sciences, Bikaner, Rajasthan 334 001 India Received: 6 February 2023; Accepted: 11 March 2024 ABSTRACT The present study was designed to assess the seasonal perturbations in key antioxidant parameters: ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) scavenging activity, lipid per oxidation (LPO), uric acid and reduced glutathione (GSH) assay along with expression profile of genes that regulate the antioxidant pathway: manganese superoxide dismutase (SOD2), Glutathione Peroxidase 1 (GPX1) and apoptosis pathway: B-cell lymphoma 2 (BCL2) and Bcl-2-associated X protein (BAX) in the two crucial indicine cattle breeds- Sahiwal and Kankrej. The study was carried out in the hot-arid region of Rajasthan across four seasons, wherein, the meteorological parameters were recorded across seasons to calculate the prevailing temperature-humidity index (THI) to assess the extent of heat load on cows. The study revealed huge diurnal variations in the temperature across four seasons, while the THI during summer and hot-humid seasons was well in excess of 80, highlighting significant heat stress on cows. All the key antioxidant parameters, except GSH registered an increase with the incremental THI. The transcriptional profile of SOD2 and GPX1 mRNA expression revealed significantly higher expression during the higher THI months of both summer and hot-humid seasons. The expression pattern of BAX and BCL2 mRNA in PBMCs of Sahiwal cows revealed an initial induction during the month of summer season with significantly higher expression, followed by a decline by the hot-humid season. The findings highlight a crucial role played by antioxidant defence and genes regulating apoptosis pathway in thermotolerance of indicine cattle breeds. Keywords: Antioxidants, Apoptosis, Bos indicus, Gene expression, Seasonal study, Temperature humidity index, Thermotolerance Present address: 1 Department of Livestock Production Management, Rajasthan University of Veterinary and Animal Sciences, Rajasthan. 2 ICAR-National Bureau of Animal Genetic Resources, Karnal, Haryana. . * Corresponding author email: mmukesh_26@hotmail.com Heat stress is a key abiotic stressor that negatively impacts animal productivity and welfare, globally (Collier et al. 2017). As the surface temperature in India has recorded an increasing trend, it presents a formidable challenge for the animal sector. The increase in intensity and frequency of heat waves in India will put dairy animals under substantial thermal stress (IPCC 2022). The already stretched resources of agriculture and livestock in the country are threatened due to unpredictable climate patterns, further worsening thermal stress on animals, especially dairy cows. Better understanding of the effects of climate on the animals and their subsequent response, will help in better management decisions, at the same time enhancing animal welfare (Polsky and von Keyserlingk 2017). Heat stress in animals have been associated with increased free radicals, especially, reactive oxygen species (ROS) production. Antioxidants are the very first line of defence against the deleterious effects of ROS, and related free radicals that are main culprits of cellular damage. The role of antioxidants in protecting the cells against various shocks can’t be stressed enough, especially when it comes to the attack of reactive oxygen species (ROS) and free radicals (Lallawmkimi 2010, Yatoo et al. 2014). The changes in antioxidant defence parameters of vertebrates in relation to the season indicates a composite disclosure of impact of various biotic and abiotic factors on the physiological state of animals (Chainy et al. 2016). The cows reared in the hot arid ambience of western Rajasthan are perpetually exposed to huge diurnal temperature fluctuations and stressful environment round the year with scorching summer, highly hot-humid and short monsoon, and very cold winters (Gujar et al. 2022). Hence, this study was an attempt to understand the key adaptations of two important indicine cattle breeds, the Sahiwal and Kankrej cows at cellular levels that aids in thermotolerance in harsh desert environment in a comprehensive manner. 45