Physiological responses of Australian Merino wethers exposed to high heat load

Alhidary, I. A., Shini, S., Al Jassim, R. A. M. and Gaughan, J. B. (2012) Physiological responses of Australian Merino wethers exposed to high heat load. Journal of Animal Science, 90 1: 212-220. doi:10.2527/jas.2011-3972

Author Alhidary, I. A.
Shini, S.
Al Jassim, R. A. M.
Gaughan, J. B.
Title Physiological responses of Australian Merino wethers exposed to high heat load
Journal name Journal of Animal Science   Check publisher's open access policy
ISSN 0021-8812
Publication date 2012-01
Year available 2011
Sub-type Article (original research)
DOI 10.2527/jas.2011-3972
Open Access Status DOI
Volume 90
Issue 1
Start page 212
End page 220
Total pages 9
Place of publication Savoy, IL, United States
Publisher American Society of Animal Science
Collection year 2012
Language eng
Formatted abstract
Twelve 9-mo-old Merino wethers (30.4 ± 3.2 kg BW) were used in a crossover study to investigate the heat tolerance of Australian Merino sheep by testing their physiological responses to repeated heat loads that occurred during summer months. Wethers were randomly divided into 2 groups of 6 wethers each, housed individually in an environmental chamber, and subjected to 2 d of thermoneutral conditions followed by either 7 d of thermoneutral (TNC; [maximum temperature, TMAX 24°C, minimum temperature, TMIN 16°C]) or 7 d of hot conditions (HOT; [TMAX 38°C, TMIN 28°C]), and then 2 d of TNC conditions. These treatments were applied in 2 replicates, each replicate in separate environmental chambers. Rectal temperature (RT) and respiration rate (RR) were measured daily at 0600, 0800, 1000, 1200, 1400, 1600, and 1800 h. Feed and water intakes were measured daily, and wethers were weighed on d 1 and d 11. Blood samples were collected from each whether on d 2 and d 6, and serum was assayed for concentrations of creatine, glucose, total protein, cholesterol, NEFA, calcium, sodium, and potassium. Exposure to high ambient temperature resulted in a 0.8°C increase in RT (P < 0.001), an increase in RR (P < 0.001) by 66 breaths per min, and a 2.7 L/d increase in water intake (P < 0.0001). Feed intake decreased by 22% (P < 0.0001), BW decreased by 5.2% (P < 0.03), and there was a reduction (P < 0.05) in the concentration of creatine. There were no differences (P > 0.05) between treatments for any of the remaining serum parameters. These results indicate that Australian Merinos were able to maintain RT within the normal range during exposure to prolonged elevated heat and recovered quickly from the negative impact of heat stress within 2 d of conditions returning to TNC. It would appear that they have a high heat tolerance and further studies are needed to examine the effects of greater heat load to determine the temperature-humidity index thresholds for Australian Merino sheep.
Keyword Heat stress
Merino Sheep
Physiological response
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Published online before print August 12, 2011

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2012 Collection
School of Agriculture and Food Sciences
School of Veterinary Science Publications
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Citation counts: TR Web of Science Citation Count  Cited 13 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 15 times in Scopus Article | Citations
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Created: Fri, 14 Oct 2011, 08:57:24 EST by Shaniko Shini on behalf of School of Veterinary Science