Veterinary Science - Theses
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ItemImpacts of heat stress on the biomarkers of oxidative stress in sheep and potential nutritional strategies for amelioration( 2015)Heat stress (HS) is a multi-billion dollar global problem as it impairs animal performance during the summer. Heat stress has been implicated in promoting oxidative stress either through excessive production of reactive oxygen species (ROS) or decreased antioxidant defence. Excessive ROS production overwhelms the antioxidant defence, and this leads to oxidative damage of biological molecules including proteins, lipids and DNA, which in turn disrupts normal metabolism and physiology. Therefore, a robust antioxidant network capable of preventing oxidative damage of biological molecules holds promise for improving the health and performance of animals during heat stress. This thesis investigated the impacts of heat stress on the oxidative stress biomarkers, elucidated potential role and optimized the dose of vitamin E and selenium required to ameliorate heat stress in sheep. The first study investigated the impact of HS and dietary antioxidant supplementation on the oxidative and physiological status of sheep. This study showed that heat stress negatively affects the oxidative status of sheep along with the physiological responses; however some of these affects can be ameliorated through dietary vitamin E (Vit E) and selenium(Se) supplementation at supranutritional concentrations. To understand the molecular mechanisms involved in heat stress ameliorative action of Vit E and Se, mRNA expression of heat shock proteins (HSP) and pro-inflammatory genes were investigated. High dietary antioxidants proved to modulate skeletal muscle expression of HSP, pro-inflammatory cytokine and NFĸB transcription factor, which may protect against HS in sheep. The potential role of high dietary Vit E or Se in amelioration of HS in sheep, and changes in acid base balance and respiratory oxidative stress biomarkers along with systemic biomarkers, were investigated in the second study. This study suggested that the hydrogen peroxide concentration in exhaled breath condensate (EBC) can be utilized as a novel biomarker to demonstrate respiratory oxidative stress induced by HS in sheep. The study also highlighted the potential of Se to reduce respiratory oxidative stress. While Vit E improved the physiological responses of heat stressed sheep; combined supplementation of Vit E and Se was required to prevent the acid base imbalance in heat stressed sheep. Finally, optimization of dietary levels of Vit E and Se to improve the performance and oxidative status of lambs finished during hot conditions was undertaken. This study suggested that supranutritional levels of dietary Vit E and Se increased average daily feed intake and the average daily gain in lambs during finishing and maintained the oxidative balance during exposure to HS. Thus it is suggested that heat stress leads to oxidative stress in sheep and supranutritional supplementation of dietary Vit E and Se can be used as a nutritional strategy to ameliorate negative effects of HS in sheep. Further research is required to elucidate the effects of dietary Vit E and Se on retail colour stability and shelf life of meat obtained from lambs finished under hot conditions.