|Gaughan, J - UNIV OF QUEENSLAND|
|Holt, S - UNIV OF QUEENSLAND|
|Hahn, G - COLLABORATOR, ARS|
|Mader, T - UNIV NEBRASKA-LINCOLN|
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 8, 2001
Publication Date: N/A
Interpretive Summary: Rate of breathing was recorded during two experiments conducted to study how feeder cattle respond to hot environments. In the first experiment (at the U.S. Meat Animal Research Center [MARC], USA), steers were exposed to hot cyclic (24C to 39C) air temperatures. In the second experiment (at the University of Queensland-Gatton [UQ-G], Australia), steers were given either daytime cooling or nighttime cooling to relieve part of the hot conditions (24C to 45C). Although breathing rate was affected by air temperature, the changes did not happen immediately as air temperatures changed. There was a lag time. Results from both studies showed that breathing rate increased with increasing air temperature, but changes in the breathing rate lagged air temperature by about 2 hr. Breathing rate can be used as a heat stress measurement, but it was dependent on several things related to the health of the animal and previous environmental experiences.
Technical Abstract: Two studies, the first in the USA and the second in Australia, were undertaken to investigate respiration rate (RR) responses of growing grain fed cattle exposed to hot climatic conditions. In the first study (Exp 1) eight Hereford x Angus x Simmental steers were exposed to 24 h cyclic hot conditions (24C to 39C). In the second study (Exp 2) six Murray Grey x Hereford steers were used. In this study ambient temperatures ranged from approximately 24C to 45C. Two cooling periods were used in Exp 2: day cooled or night cooled. In each study RR was measured over three 24 h periods and generally increased as ambient temperature increased. However, the rate of change was not constant either between studies or over time. In Exp 2, day cooled cattle typically showed an increase in RR at night when ambient temperature was decreasing. In both studies RR lagged behind ambient temperature by approximately 2 h. Respiration rate can be used as an indicator of heat stress in cattle, provided animal condition, prior exposure, ambient conditions (increasing or decreasing ambient temperature) and previous cooling strategies are considered.