Effect of prolonged exposure to continuous heat and humidity similar to long haul live export voyages in Merino wethers
C. A. Stockman A D , A. L. Barnes A , S. K. Maloney B , E. Taylor A , M. McCarthy C and D. Pethick A
+ Author Affiliations
- Author Affiliations
A School of Veterinary and Biomedical Sciences, Murdoch University, Perth, WA 6150, Australia.
B School of Biomedical Biomolecular and Chemical Sciences, University of Western Australia, Perth, WA 6009, Australia.
C Professional Agricultural Services, Fremantle, WA 6595, Australia.
D Corresponding author. Email: c.stockman@murdoch.edu.au
Animal Production Science 51(2) 135-143 https://doi.org/10.1071/AN10120
Submitted: 21 July 2010 Accepted: 8 November 2010 Published: 28 January 2011
Abstract
This experiment investigated the physiological responses of Merino wethers (n = 12) to prolonged high heat and humidity similar to that experienced during long haul, live export voyages from Australia to the Middle East. Merino wethers were randomly assigned to individual pens in rooms with a controlled environment, and exposed to gradually increasing temperatures, and two exposures of 3–4 days of sustained high heat and humidity, up to a maximum of 31°C wet bulb temperature (37°C dry bulb and 67% relative humidity). There was 1 day at thermoneutral temperatures separating the heat exposures. The core temperatures and respiratory rates of Merino wethers increased during both heat exposures, with open-mouthed panting observed during both exposures. Plasma partial pressure carbon dioxide (pCO2) and bicarbonate concentration (HCO3–) decreased, and plasma pH increased during the second heat exposure. Both pCO2 and HCO3– returned to normal immediately following the heat exposures. Feed intake was maintained during the heat exposures. There were no large alterations in blood electrolyte concentrations attributable to the effects of the heat. The results show that Merino wethers experienced significant physiological changes during exposure to prolonged and continuous high heat and humidity, but maintained most aspects of homeostasis despite being hyperthermic and recovered quickly when conditions returned to thermoneutral.
Additional keywords: acid–base, ovine, stress.
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