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The Effect of the Nutritional Plane upon the Reactions of Animals to Heat

University of Queensland¹

Abstract

It is often desired to raise heavy or fat animals in hot climates but conflicting ideas are held as to whether heavy feeding renders them unsuitable for tropical and subtropical conditions.

Experiments were carried out with White Leghorn hens, Australorp hens, Middle White sows and cross-bred Border Leicester-Merino ewes, in which some animals of each kind were reared upon a high-plane diet and some upon a low-plane diet. Once a week each animal was exposed to a hot atmosphere for seven hours. Hot-wet and hot-dry atmospheres were used on alternate weeks. The behavior of the rectal temperature, pulse rate, respiratory rate and weight loss was measured.

It was found that, in all animals studied, the reactions of the high-plane animals to hot conditions were significantly higher than those of the low-plane animals. This was much more pronounced under the hot-dry conditions. When, after several weeks, the diets of hens and ewes were reversed, the relative reactions of the two groups upon exposure to heat were reversed much more rapidly than the body weights.

In another series of experiments, animals were fed successively upon different diets which were of equal caloric value but contained proportions of protein varying from 5 to 28.5 percent. Hens, a dog, a ewe and a sow were used. After a week's feeding with a particular diet, the animals were exposed to a critically hot atmosphere for seven hours and the reactions studied. In no case was any evidence obtained that a high proportion of protein had any significant effect upon the reactions of the animals to heat.

It is concluded that the caloric value of the current diet has a significant, and at times practically important, effect upon the reactions of animals to hot conditions, but the proportion of protein contained in the diet is of no significant moment.

¹ Department of Physiology, University of Queensland, Brisbane, Australia. The experiments reported were carried out under a grant made available through the Commonwealth Research Projects Scheme arranged for universities by the Council for Scientific and Industrial Research. H. M. Whyte carried out the protein-feeding experiments and H. J. G. Hines arranged the diets.