DOMESTIC MAMMAL ADAPTATIONS 



environment (Fig. 6). This is especially true in the relatively cool 

 months of May and June. When it gets extremely hot in July and 

 August, the fluctuations of body temperature become greater. 



One may define the effectiveness of temperature regulation as 

 the quotient of the change in the environmental temperature and the 

 changes in the body temperature. 



Figure 7 shows this calculation for the cow observed by Ittner 

 (1946) in the Imperial Valley. 



As long as the maximum temperature of the environment stays 

 below 40 C, the change in the cow's body temperature is only about 

 one fortieth of the change in the environmental temperature, but when 

 the maximum temperature of the air reaches 44 G, as in July, the 

 cow's regulating efficiency drops to one half. Her temperature fluc- 

 tuation now becomes one twentieth of that of the environment. The 

 cow is better equipped to maintain her body temperature against a 

 cold than against a hot environment. 



Some breeds of Asiatic cattle are better adapted to hot climates 

 than Western breeds. The Zebu cattle may thrive under conditions 

 under which Western cattle suffer. Brody and his coworkers have 

 investigated this difference and McDowell and his coworkers (1953) 

 have studied the inheritance of this adaptation. They crossed Jersey 

 cattle with Sendhi, a breed of Zebus, and exposed Jerseys and cross- 

 breeds to an environmental temperature of 10 5 F(40 C) for 6 

 hours. Figure 8 shows some of their results. The crossbreeds main- 

 tain a body temperature close to 102° F (39 C), whereas^the body 

 temperature of the Jersey cows rises to over 103 F (39 C). The 

 reaction of the Jerseys depends on the season. During the winter 

 months they are least able to cope with a 6 hour exposure to 10 5 F 

 (40° C), whereas during the summer months this exposure raises 

 their body temperatures to a level not much higher than that of the 

 crossbreeds. 



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