ABSTRACT The focal point of this limited review is bioenergetic research conducted in the Biological Engineering Research Unit at the U.S. Meat Animal Research Center (MARC), using recently developed instrumentation and analytical techniques. The dynamics of observed thermoregulatory responses in cattle to thermal heat load challenges are explored, with an emphasis on physiological and behavioral parameters of body temperature, respiration rate, and feed intake. Observations of body temperature, especially tympanic temperature, have shown 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 has been found to be robust for objectively differentiating among responses of cattle in cool to hot environments, and it indicates a stress threshold of approximately 25oC (coincident with declining feed intake). Other analyses determined a 21oC threshold for increased respiration rate. The reported observations and analyses provide further understanding of how and why the animals respond to environmental challenges, an understanding that is necessary for refining performance models and developing 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.
Implications Evaluation of the dynamics of bioenergetic processes for cattle in non-stressing and stressing thermal environments as part of a long-term research program at the USMARC has strengthened our knowledge of how and why animals respond as they do to environmental challenges. This knowledge provides a basis for practical environmental management, as well as an understanding necessary to develop and refine performance, energetic and thermoregulatory models.
Key Words: Thermal Energy, Stress, Thermoregulation, Animal Husbandry
© 1999, by the American Society of Animal Science and the American Dairy Science Association. All rights reserved.
AM Symp. 10-20