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Journal of Dairy Science Vol. 43 No. 9 1245-1254
© 1960 by American Dairy Science Association ®
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A Study of the Influence of Solar Radiation on Physiological Responses of Dairy Cattle1

J. S. Williams2, R. R. Shrode3, R. E. Leighton and I. W. Rupel

Departments of Dairy Science and Genetics, Texas Agricultural Experiment Station, College Station

ABSTRACT

Effects of the subtropical climate of central Texas on the heat-regulatory ability of dairy heifers were studied in 1955 and 1956. Physiological responses of the heifers—body temperature, pulse rate, and respiration rate—to environmental effects—air temperature, solar radiation, vapor pressure, and wind velocity—were studied. The effects of solar radiation were of primary interest.

Solar radiation had a direct effect on body temperature when air temperatures where close to the range of thermo-neutrality (below 90° F.). In higher air temperatures (above 90° F.), solar radiation had little effect on the changes in body temperatures. Respiration rate, the most consistent physiological response studied, was affected more by solar radiation than by the other wheather influences. Large differences in respiration rate due to genetic origin were also observed. It could not be demonstrated satisfactorily that pulse rates were influenced by any of the environmental variables.

Body temperature data and respiration rate data taken on animals in the absence of direct solar radiation were almost as reliable indicators of differences in heat regulatory ability as the same measurements taken on animals in the presence of direct solar radiation.

FOOTNOTES

1 The data on which this paper is based were collected in studies conducted as part of a project supported cooperatively by the Texas Agricultural Experiment Station and the Dairy Cattle Research Branch, Agricultural Research Service, United States Department of Agriculture.

2 Present address: Department of Experimental Statistics, North Carolina State College, Raleigh, North Carolina.

3 Present address: The William H. Miner Agricultural Research Institute, Chazy, New York.






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