The effects of plane of nutrition and environmental temperature on the energy metabolism of the growing pig

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Abstract
1. The heat losses and energy balances of thirty-eight individually housed pigs (initial body-weights 21–38 kg) were measured continuously for periods of 14 d when they were maintained at environmental temperatures of 10, 15, 20, 25 or 30°. At each temperature four levels of feeding were given approximating to once, twice and three times the maintenance energy intake and the ad lib. level. The minimal maintenance energy requirement (M) was calculated to be 440 kJ metabolizable energy (me)/kg0.75 per d at 25°.2. me intake at the ad lib. level decreased from 1965 kJ/kg0.75 per d at 10° to 1202 at 30°.3. Heat loss calculated from multiple regression analysis decreased to minimum levels between 20 and 25° 30° was within the hyperthermic zone at each plane of nutrition.4. The partition of heat loss into its sensible and evaporative components showed that evaporation increased from 25% at 10° to 78% at 30°.5. Critical temperature was dependent upon food intake and decreased from 23.1° at M to 20.7° at 2M, 18.0° at 3M and 16.7° at 4M.6. The extra food required to meet extra thermoregulatory heat production per 1° below the effective critical temperature was 0.65 g/kg body-weight per d.