Heat losses from young pigs at three environmental temperatures, measured in a direct calorimeter

Abstract

1. A direct calorimeter is described, capable of partitioning the total heat loss from individual pigs into its evaporative and non-evaporative components; tests revealed that the instrument measured non-evaporative heat loss with a coefficient of variation of 3%, and evaporative heat loss with a coefficient of variation of 5·0% at 10° and 20°C, and 5·6% at 30°C.2. Experiments were carried out to measure the differences between heat losses at 20° and 9°C, or at 20° and 30°C, for pigs weighing approximately 26 kg and 64 kg; each measurement lasted 20 minutes and was made after an equilibration period of 3–4 hr.3. Heat loss was proportional to body weight raised to the power of 0·6, under the present experimental conditions, over the range 26–64 kg at 20°C.4. Total heat loss at 9°C was significantly greater than at 20°C for pigs of both sizes; total heat loss at 30°C was smaller than at 20°C for pigs of both sizes, the decrease being significant for the heavier pigs only. Nonevaporative heat loss increased significantly with decrease in temperature. Evaporative heat loss at 30°C was significantly greater than at 20°C. The increases in total and non-evaporative heat losses at 9°C when compared with 20°C, were significantly greater for the lighter pigs than for the heavier pigs. The small decrease in total heat loss at 30°C, compared with 20°C, may have been due to non-attainment of thermal equilibrium at 30°C.5. Values for whole body thermal conductance were calculated from the measurements of non-evaporative heat loss, and these indicated that a change in tissue conductance took place between 20° and 30°C; the mean values at 9°C were 3·78 and 3·15 kcal/°C.m2.hr for the lighter and heavier pigs respectively.6. Evaporative heat loss at 20°C amounted to 280 and 330 kcal/m2. 24. hr for the lighter and heavier pigs respectively. This component of heat loss amounted to 8% and 13% of the total heat loss at 9° and 20°C respectively for all pigs; the corresponding values at 30°C were 32% and 25% for the lighter and heavier pigs respectively. The increased evaporative loss at 30°C was accompanied by an increase in respiratory rate.7. These results agreed well with the results of previous work with groups of pigs, for heat loss at 20°C. Comparisons with that work indicate that the increase in heat loss at 9°C, when compared with 20°C, was greater for individual pigs than for groups of pigs, of both sizes.