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The Heat Production of Cattle in a Respiration Calorimeter as Related to the Rate of Ventilation and to the Moisture Content of the Air

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

The heat production of a dry cow, on a constant ration, was measured in a respiration calorimeter by direct and also by indirect calorimetry, in eight consecutive twenty-four hour intervals of observation, to determine the effects of the rate of ventilation of the calorimeter on the paths of outgo of heat from the animal and on the quantity of the total heat produced.

The rate of ventilation was rapid or slow in alternate twenty-four hour intervals, the rapid rate being about 35,000 liters per hour, and the slow rate from 5,414 to 5,454 liters per hour; and in the second four of the eight intervals of observation about 85 per cent of the moisture was removed from the ingoing air by freezing.

The carbon dioxide content of the outcoming air at the slow rate of ventilation was 10.3 times as great, and at the high rate of ventilation 1.8 times as great, as that permitted by King's standard (4) (.167 per cent) for barn ventilation.

The moisture content of the outcoming air at the slow rate of ventilation was 1.4 times as great as at the rapid rate,—a large proportion of the moisture given off by the animal having been condensed on the cooling system of the calorimeter.

With both methods of determination of the heat production there was, with each change in the rate of ventilation from rapid to slow, a slight decrease in the heat production; and with each change from slow to rapid, a slight increase in the heat production.

Approximately 40 per cent of the heat produced was eliminated by the animal as latent heat of water vapor, the quantity of which generally decreased to a slight extent with decrease in the rate of ventilation.

Inasmuch as the carbon dioxide content of the outcoming air at the slow rate of ventilation averaged 1.725 per cent, whereas a carbon dioxide content of 1.0 per cent is ample for satisfactory respiratory quotient calorimetry, the authors conclude that it is unlikely that the rate of ventilation would affect the heat production in respiratory quotient calorimetry if the respiration chamber is equipped with an adequate cooling device.

Manuscript received 10 October 1931.