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The Analysis of the Curve of Heat Production in Relation to the Plane of Nutrition

(From the Institute of Animal Nutrition, Pennsylvania State College, State College, Pa.)

The curve of heat production of cattle, between points of fasting and three times the maintenance requirement, is analyzed by computation and graphic representation of the contributions of heat from the katabolism of protein, fat, and carbohydrate.

The derivation of heat from body substance and from food nutrients is shown, as also is the energy expense of synthesis of fat.

The contribution from protein is about the same proportion of the total heat production at all planes of nutrition.

The contribution of fat is 83.4 to 86.1 per cent of the total heat production at fasting, and apparently falls to zero at maintenance.

The proportionate contribution of carbohydrate between fasting and maintenance is approximately the complement of that of fat. From maintenance to three times maintenance the proportionate contribution of carbohydrate does not vary greatly.

The energy cost of fat synthesis is a minor factor, above maintenance.

The causes of the curvature of the line representing the relation of the heat production to the food consumption of cattle, with rise in the plane of nutrition from fasting to full feed, seem to be virtually as suggested in former publications, 1.—the increase in intermediary metabolism resulting from increasing concentration of circulating metabolites, 2.—the decrement of waste heat of utilization of body nutrients, between fasting and maintenance, 3.—changes in the proportions of protein, fat, and carbohydrate katabolized, and probable (but unestablished) differences in the specific dynamic effects of these different katabolized nutrients, 4.—the energy expense of synthesis of fat from carbohydrate, above maintenance, and 5.—the decreasing metabolizability of the food at the higher planes of nutrition, 6.—the heat of fermentation of carbohydrate nutriment, and 7.—the physical work of food utilization.