KLEIBEF 



environmental temperature. As they get warmer, their breath rate 

 increases rather gradually, so that the relation between respiratory 

 frequency and the environmental temperature can well be expressed 

 by the Arrhenius equation. 



Figure 14 shows the logarithm of respiratory frequency plotted 

 against the reciprocal of the environmental temperatiire in degrees 

 Kelvin. 



The idea that cows do not perspire at all through their body 

 surface has been proven erroneous. Figure 15 summarizes the 

 results of Kibler and Brody (1952), which indicate that indeed 

 a great part of the heat given off by cows, especially in a hot 

 environment, is accounted for by surface evaporation, and the 

 evaporation in the respiratory system amounts to only one- 

 third of the total evaporation. 



Kibler and Yeck (1959) later observed that the greater heat 

 tolerance of Brahman cattle compared with shorthorns is related 

 to a greater evaporative capacity and that in particular the ratio 

 of skin evaporation to respiratory evaporation is greater in the 

 heat tolerant Brahmans. The major advantage of the Brahmans, 

 however, in combating overheating, according to Kibler and 

 Brody (1954), is their relatively low metabolic rate, about 80 

 kcal/(m X hr) as compared with 150 kcal/(m x hr) in Jerseys 

 and Holsteins. 



The Method of the Camel 



The most ingenious system of keeping cool has been develop- 

 ed by the camel, also known as the ship of the desert. The U. S. 

 Navy has a perfectly good reason, therefore, for supporting re- 

 search on this animal by Knut and Bodil Schmidt- Nielsen, a 

 team of extraordinarily keen observers. 



The camel apparently realizes the advantage of inside cooling as 

 opposed to surface cooling. It also is very much interested in the 

 most economic useof water and can hardly afford to have sweat drop 

 to the ground un evaporated, as it does in human athletes and in 



264 



