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The Critical Temperature for the Albino Rat as Affected by Feeding¹

One Figure

Institute of Animal Nutrition, Pennsylvania State College, State College

The heat production of fourteen mature male albino rats receiving a constant feed intake was determined in 121 7-hour periods of observation at environmental temperatures ranging from 12° to 34°C. Feeding did not lower the temperature of minimum heat production below 30°C.—the critical temperature for the fasting rat.

In another group of young rapidly growing rats, on full feed, the zone of thermal neutrality was still unchanged.

The prevailing opinion that feeding lowers the critical temperature, therefore, was not found true in relation to the albino rat under the conditions of experimentation.

At environmental temperatures below 25°C. the curves of heat production for rats receiving feed were approximately the same as for fasting rats, when computed to a basis of the same live weight.

At environmental temperatures above 25°C. the heat production of the rats receiving feed was higher than that of the fasting animals, as determined by the plane of nutrition and the dynamic effect of the feed.

The percentage of total heat eliminated as water vapor remained constant at temperatures from 12°C. to 32°C. With further rise in environmental temperature there was a sharp increase in both the amount and the percentage of heat eliminated as latent heat of water vapor.

It is not concluded from this investigation that the critical temperature of the environment for animals in general is unaffected by feeding.

Manuscript received 8 September 1942.