Diurnal variation in the thermal demand of growing pigs

Abstract 1. 1.|Six experiments, each with 15 or 16 pigs weighing 30–46 kg, were performed. Each lasted 30 or 36 days. Feeding levels were 93 g kg −0.75 (experiments 1 to 4) and 83 g kg −0.75 (experiments 5 and 6). Ambient temperature ( T a ) was changed in stepwise fashion every 2–3 days by 2 to 4 K between 23 and 8°C. Between steps T a remained constant (experiments 1–3 and 5) or fluctuated 2.5 K above and below the daytime and night time means (experiments 4 and 6) until 8°C. At each step heat production (HP) was measured continuously during successive 18-min periods over 24 or 48 h. 2. 2.|In experiments 1 and 2 HP increased below 13 to 14°C and in experiment 3 to 6 below about 20 to 23°C. 3. 3.|HP per day increased from 12.9 to 14.3 kJ kg −0.75 day and from 9 to 9.6 kJ/kg −0.75 day in the constant and fluctuating temperature regimes, respectively. 4. 4.|Data showed that the total thermal demand was less during the night than during daylight hours.