|Hahn, G - MARC COLLABORATOR|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 1999
Publication Date: N/A
Interpretive Summary: This review explores how cattle respond to the challenges of hot weather, especially in terms of respiration rate, body temperature regulation, and feed intake. The focal point of the review is research conducted since 1982 in the Environmental Laboratory at the U.S. Meat Animal Research Center. Observations made during that research provide further understanding of how and why the animals respond as they do to the hot- weather challenges. Those observations provide a basis for refining performance models and establishing thresholds for proactive environmental management of cattle during hot weather.
Technical Abstract: This review explores the dynamics of observed thermoregulatory responses in cattle coping with thermal heat load challenges, emphasizing the physiological and behavioral parameters of body temperature, respiration rate, and feed intake. The focal point of the review is research conducted in the Biological Engineering Research Unit at the U.S. Meat Animal Research Center (USMARC), using newly-developed instrumentation. Observations of body temperature, especially tympanic temperature, showed hot environments to cause phase shifts, increased amplitude and increased means for diurnal rhythms. Fractal analysis of body temperature records obtained at 2 to 10 min intervals was shown to be a robust method for objectively differentiating among responses of cattle in moderate to hot environments, and indicate a stress threshold of about 25C (coincident with declining feed intake). A threshold for increased respiration rate was found at 21C. The reported observations provide further understanding of how and why the animals respond as they do to environmental challenges, necessary for refining performance models and the development of energetic and thermoregulatory models. The dynamic responses are discussed in the context of establishing criteria for proactive environmental management for cattle during hot weather, using heat waves as an example.