THE RESPONSE OF GROWING PIGS TO HIGH CYCLIC AND CONSTANT TEMPERATURES (ENERGETICS, HEAT PRODUCTION, CALORIMETRY, FEED CONSUMPTION)

The energetic response of growing pigs to high temperature conditions was investigated with indirect calorimetry. One calorimeter was maintained at a constant 33(DEGREES)C air temperature with an average dewpoint of 23(DEGREES)C while air temperature of the second calorimeter was maintained between a maximum of 40(DEGREES)C at 1400h and a minimum of 26(DEGREES)C at 530h with a temperature pattern of a quarter cycle sine wave between the maximum and minimum temperature resulting in a mean daily temperature of 33(DEGREES)C. Each calorimeter housed four 36-kg pigs. Feed and water consumption, oxygen, carbon dioxide and water vapor concentrations, temperatures, and air mass flowrates were measured every four minutes during the latter nine days of each of the four 12-day replicates. Hourly respiratory rates and forehead surface temperatures also were measured during the third replicate. Blood pressure, carotid artery temperature, and activity were recorded by a portable micro-processor controlled data logger. During the afternoon period, the highest (129 W/pig) and lowest (105 W/pig) heat production rates occurred in the cyclic and constant temperature treatment, respectively. The mean daily heat production rates were 122 and 117 W/pig and the respiratory rates were 115 and 79 br/min for these treatments, respectively. Daily metabolizable energy intake remained constant for the treatments and time (17.3 MJ/(d.pig)). The constant and cyclic temperature pigs consumed a maximum amount of feed during the evening (32%) and early morning period (34%), respectively. A major shift in feed consumption occurred from the evening to the early morning period during acclimation. Metabolizable feed energy intake and heat production values were similar ((+OR-)20W) during the late morning, afternoon and late night periods. The feed consumption rates of the cyclic temperature pigs were maximum at the time the lights were switched on or off. The forehead surface temperature is a reliable indicator of sensible heat production. The pig latent heat production was 81 W at 33(DEGREES). The principal component analysis indicated that the energetics of the pigs can be described by feeding activity, growth, heat stress, and energy output. The experimental data were used to improve an existing energetics model and to expand the data base