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The Relationship of Surface Area to Heat Tolerance in Jerseys and Sindhi-Jersey (F₁) Crossbred Cows¹

U. S. Department of Agriculture

Abstract

The surface area was measured on 20 adult Jersey and 20 adult Sindhi-Jersey crossbred cows with a surface integrator, the construction and use of which is described. The areas were compared with the body weights. Neither the ratio of surface area to body weight, nor the ratio of surface area to the two-thirds power of body weight, showed a significant difference between the two groups.

In spite of the close similarity in proportional surface area, the heat tolerance of the two groups was markedly different. This indicates that differences in heat tolerance of animals such as these are not primarily due to differences in proportional surface area even though the presence of large dewlaps, etc., might suggest that such a difference in surface area would be found.

The relationship between surface area and body weight in the animals reported here, and in animals of adult size reported elsewhere in the literature, is well enough expressed by a straight line. It is suggested that there is no advantage to be gained from the more complex exponential relationship introduced by using a fractional power of body weight when comparisons are to be made between adult animals.

¹ These studies were conducted by the Bureau of Dairy Industry at the Agricultural Research Center, Beltsville, Maryland.

² Professor of Physiological Climatology, Johns Hopkins University, Baltimore, Md.

³ Mason (1951) defines Brahman as "originated from Ongole, Kankrej, Gir, and Kishma Valley breeds imported 1850–1906, probably with some European blood."