The effect of ambient temperature on diurnal rhythm in heat production and activity in pigs kept in groups

The effect of ambient temperature on diurnal rhythm of metabolic rate and activity was studied in group housed pigs in two trials. Two climate controlled respiration chambers were used, one for each trial. Each chamber contained two groups of 8 pigs. During the experiment of 31 days the mean live weight of the animals increased from 28 to 40 kg. Feeding level was kept constant at 93 kg−0.75. d−1. Feed contained 12 kJ of metabolizable energy per g. Temperature treatment started with 20‡C for two days. After that it was lowered in stepwise fashion by 4K to 16, 12 and 8‡C. Each temperature treatment lasted two days. After that temperature it was increased in steps to 20‡C in 8 days. The whole procedure was repeated once. Metabolic rate and activity were measured continuously during the 24 hrs of every second day of the temperature treatment. Metabolic rate increased at temperatures below 16‡C. Activity was associated with ambient temperature. At low temperature, the total activity related heat production was increased, especially during day time. Variation in metabolic rate within a day was not reduced by low ambient temperature. Thermal requirement, calculated as lower critical temperature, was about 14‡C as averaged over the day, (16.1‡C during day time and 13.6‡C during night time). Extra thermal heat production below thermoneutrality was affected by time of day and activity.