title: Dietary antioxidants at supranutritional doses improve oxidative status and reduce the negative effects of heat stress in sheep.
abstract: The present study was undertaken to investigate the impact of heat (thermal) stress and dietary antioxidant supplementation on the oxidative and physiological status of sheep. Twenty-four Merino × Poll Dorset crossbred ewes were housed in 1 of 2 climatic chambers (thermoneutral or heat stress) and offered either a control (10 IU vitamin E/kg DM and 0.24 mg Se/kg DM) or high antioxidant (100 IU vitamin E/kg DM and 1.20 mg Se/kg DM) diet. The sheep were exposed to 2 thermal (temperature) treatments (thermoneutral [TN]: 18-21°C and 26-30% relative humidity; and heat stress [HS]: 28-40°C and 40-50% relative humidity) for 2 wk in a single reversal design. After 1 wk of dietary treatment, animals in 1 chamber were subjected to HS for 1 wk, with the temperature being increased to 40°C between 0900 and 1700 h and then maintained at 28°C overnight. Those sheep in the TN group were maintained at 18 to 21°C. Physiological parameters were recorded 4 times a day (0900, 1300, 1700, and 2100 h) and blood samples were collected on d 1 and 7 of heat treatment. Plasma samples and red blood cell lysates were assayed for oxidative stress biomarkers. The thermal treatments were then reversed and the above measures repeated. All measured physiological parameters were elevated (P < 0.001) by thermal treatment. Respiration rate was lower during HS in sheep supplemented with antioxidants as indicated by a diet × temperature × time interaction (P = 0.010). There was 13% decline (P = 0.014) in feed intake of the unsupplemented animals during HS whereas the same was maintained in sheep supplemented with high doses of antioxidants. Plasma reactive oxygen metabolites concentrations were reduced (114 vs. 85 units/dL; P < 0.005) while biological antioxidant potential tended to be increased (3,688 vs. 3,985 μmol/L; P = 0.070) in heat stressed sheep supplemented with antioxidants. The oxidative stress index was 30% lower (P < 0.001) in supplemented sheep (2.16 ± 0.06 arbitrary units) during HS than in unsupplemented sheep (3.12 ± 0.08 arbitrary units). Plasma advanced oxidation protein products tended (P = 0.070) to decrease in antioxidant supplemented heat stressed sheep as compared to their unsupplemented counterparts. It was concluded that heat stress negatively affects the oxidative status of sheep along with the physiological responses and some of these affects can be ameliorated through dietary antioxidants supplementation at supranutritional concentrations.
authors.affiliation: Department of Animal Husbandry, Government of Himachal Pradesh, Shimla 171005, India Melbourne School of Land and Environment, The University of Melbourne, Parkville, Vic. 3010, Australia chauhans@student.unimelb.edu.au.
authors.forename: S S
authors.initials: SS
authors.lastname: Chauhan
authors.affiliation: Melbourne School of Land and Environment, The University of Melbourne, Parkville, Vic. 3010, Australia Faculty of Veterinary Science, University of Sydney, Sydney, NSW 2570 Australia.
authors.forename: P
authors.initials: P
authors.lastname: Celi
authors.affiliation: Melbourne School of Land and Environment, The University of Melbourne, Parkville, Vic. 3010, Australia.
authors.forename: B J
authors.initials: BJ
authors.lastname: Leury
authors.affiliation: Department of Physiology, Monash University, Vic. 3800, Australia.
authors.forename: I J
authors.initials: IJ
authors.lastname: Clarke
authors.affiliation: Melbourne School of Land and Environment, The University of Melbourne, Parkville, Vic. 3010, Australia.
authors.forename: F R
authors.initials: FR
authors.lastname: Dunshea
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage / Q000494:pharmacology*; D015415:Biomarkers / Q000097:blood; D001831:Body Temperature / Q000502:physiology; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D005260:Female; D018882:Heat Stress Disorders / Q000503:physiopathology / Q000517:prevention & control / Q000662:veterinary*; D006358:Hot Temperature / Q000009:adverse effects; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D017382:Reactive Oxygen Species / Q000097:blood; D012643:Selenium / Q000008:administration & dosage / Q000494:pharmacology; D012756:Sheep / Q000502:physiology*; D012757:Sheep Diseases / Q000097:blood / Q000503:physiopathology / Q000517:prevention & control*; D014810:Vitamin E / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D015415:Biomarkers; D017382:Reactive Oxygen Species; D014810:Vitamin E; D012643:Selenium
keywords: antioxidants; heat stress; oxidative stress; sheep