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The thermal response of sheep to a hot environment in different years

Published online by Cambridge University Press:  27 March 2009

G. J. McCrabb ,
G. Bortolussi ,
L. M. Hennoste  and
B. J. McDonald
G. J. McCrabb
Affiliation:
Department of Physiology, Monash University, Clayton, Victoria 3168, Australia
G. Bortolussi
Affiliation:
Toorak Research Station, Queensland Department of Primary Industries, Julia Creek, Queensland 4823, Australia
L. M. Hennoste
Affiliation:
Toorak Research Station, Queensland Department of Primary Industries, Julia Creek, Queensland 4823, Australia
B. J. McDonald
Affiliation:
Toorak Research Station, Queensland Department of Primary Industries, Julia Creek, Queensland 4823, Australia
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Summary

The aim of this experiment was to determine whether the thermal responses ofsheep exposed to a hot environment were similar in different years. Rectal temperaturesofsheep were measured during the hot months (between November and March) of three consecutive years (1990/91, 1991/92, 1992/93) in a flock of Merino sheep (n = 151) in the semi–arid tropics of northern Australia. Mean daily maximum temperatures in these months were 36±0·4, 39±0·3 and 37±0·3°C in Years 1, 2 and 3, respectively. In Year 1, rectal temperatures were measured on 3 consecutive days;the repeatability was 0·47 at 08·00 h and 0·64 at 16·00 h. In Year 1, two sub-groups were identified according to measurements of rectal temperature, low body temperature(LBT; n = 35) sheep, whose rectal temperature was ≤ 39·8°C at 16·00 h on each of the 3 consecutive measurement days, and high body temperature (HBT; n = 32) sheep, whose rectal temperature was ≥ 39·9°C. The rectal temperatures of LBT and HBT sheep were then measured during the subsequent 2 years. Rectal temperatures of HBT sheep were significantly higher than those of LBT sheep at both 08·00 and 16·00 h, in both Year 2 and Year 3. Rectal temperatures at 16·00 h in Year 1 were correlated (P < 0.001) with rectal temperatures at 16·00 h in both Year 2 (r = 0·79) and Year 3 (r = 0.82), respectively. It was concluded that measurement of rectal temperature in sheep exposed to a hot environment in any oneyear is an accurate index of their rectal temperatures during subsequent years.

Type
Animals
Information
The Journal of Agricultural Science , Volume 125 , Issue 1 , August 1995 , pp. 153 - 158
Copyright
Copyright © Cambridge University Press 1995

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