Effect of heat stress on superoxide anion production in native and crossbred cattle under in vitro whole blood culture model

摘要

Impact of global warming on the dairy industry has gained attention due to huge economic losses through low production and fertility caused by heat stress. Exposure to hyperthermia provokes a series of complex responses in mammals which are been related to morphological and physiological alterations including the production of reactive oxygen species (ROS). A quantitative spectrophotometric based nitroblue tetrazolium (NBT) reduction assay was used to estimate the superoxide anion (center dot O-2(-)) level in heat stressed (at 42 degrees C) whole blood cultures of native and crossbred bulls (Sahiwal and Frieswal), in vitro. The breed effect in the kinetics of center dot O-2(-) production at different time periods of continual heat stress was analyzed by repeated measures ANOVA. Comparison between different time periods in reference to 37 degrees C was analyzed by paired t-test. The center dot O-2(-) level was significantly different (p 0.05) between cells at 37 degrees C and 42 degrees C at different periods of incubation. Kinetics study showed increment of center dot O-2(-) production on the acute phase of stress followed by a reduction in both Sahiwal and Frieswal breeds. In Sahiwal breed, the inflated superoxide level continued abated till 4 h and raised again at 6 h, while in Frieswal center dot O-2(-) level reverted to raise sooner with in 2 h of incubation itself. Contrarily, kinetic of center dot O-2(-) level in plasma showed a significant reduction (p 0.001) at 30 min of 42 degrees C incubation followed by increment of center dot O-2(-) level. Further, the breed variation was significant (p 0.05) and a significant high reduction of center dot O-2(-) level was observed in Sahiwal breed. Our finding indicates that, a better and longer center dot O-2(-) production homeostasis and higher plasma scavenging ability of native breed may be one of the reasons for the higher thermal tolerance of these breeds in tropical climate.