LAUSR

Abstract The study was conducted the seasonal effect on mitochondria activity-related genes [Succinate dehydrogenase (SDH), Citrate synthase (CS) and mitochondrial transcription factor-A (TFAM)] and heat shock protein (HSP) genes in spermatozoa of Karan Fries (Tharparkar X Holstein Friesian) bulls. Five (n = 5) adult healthy bulls were selected from Artificial Breeding Research Centre of National Dairy Research Institute, Karnal. Thirty (30) ejaculates were collected during summer and winter using artificial vagina (42–45 °C). The ambient temperature, relative humidity, dry and wet bulb temperatures were recorded during the study. Total RNA was isolated by Trizol method. The mRNA expression of SDH, CS and TFAM was lower during summer compared to winter season. The expression of HSP70.1, HSP70.2, HSP90 and HSP105 was higher (p  <  0.05) during summer than winter season. However, the expression of HSP70.8 was non-significantly higher during summer season. The physical analysis of semen (volume, motility, live spermatozoa, hypo-osmotic swelling test, concentration, acrosome integrity, total sperm out, major abnormalities) was affected significantly (p  <  0.05) by the summer season. The antioxidant enzymes (glutathione peroxidase, superoxide dismutase, glutathione reductase and total antioxidant capacity) and malondialdehyde (product of lipid peroxidation) concentration were estimated higher (p  <  0.05) during the summer season than winter. The semen quality of Karan Fries bulls is affected considerably during summer season in tropical climatic conditions.