INFRARED HEAT FOR WEANLING PIGS: A BIOENERGETICS ANALYSIS

The weanling pig\u27s responses to infrared heat were described by measuring their rates of heat production, metabolizable energy intake, and energy retention on days 1,2,4, and 6 after weaning. The mean age and body mass were 21 d and 6.4 kg, respectively, when the pigs were weaned. Four treatments received a 20 C air temperature combined with an effective radiant field (ERF) of 0, 50, 87, or 113 W/m(\u272) supplied by electric infrared heaters. Mean radiant temperatures (MRT) were 20, 28, 34, and 39 C, respectively. Another treatment, representing current recommendations for nursery pig environments, received an air temperature of 28 C and no infrared heat. All treatments were replicated six times with individual pigs as experimental units. An infrared heater was suspended above each of six indirect calorimeters that contained a single pig. A 0.05 mm polyethylene enclosure formed the outer shell of the calorimeters, which were contained within an insulated chamber. Electronic gas analyzers measured instantaneous CO(,2), O(,2), and H(,2)O concentrations in each calorimeter at 28-minute intervals. Feed consumption was measured daily and all energy balances were calculated on a 24-hr periods. Feed and water were available ad libitum. The metabolizable energy content of the feed was 13.5 kJ/g dry mass. Regression equations were developed to describe the rates of total and latent heat production and energy intake as functions of MRT, air temperature and black globe temperature. Mean radiant temperature was the best parameter for describing the energy balances in this study. All treatments had the highest rate of total heat production (HPR) during the first day post weaning, and the rates declined to a minimum 2-4 days afterwards. Over the range of conditions in this study, the pigs adjusted total heat production rates by changing only the rate of sensible heat production. Increasing irradiation reduced both feed intake and metabolic heat production; but, for each unit increase in ERF, energy intake decreased more than heat production. Six days after weaning, mean energy retention rates for pigs at 20 C were 4.4, 4.6, 3.7, and 2.7 W/kg(\u270.75) in the 0, 50, 87, and 113 W/m(\u272) treatments, respectively. At the same time, the energy retention rate was 5.4 W/kg(\u270.75) for pigs given no infrared heat and 28 C air temperature