Two experiments were performed to study the effect of ambient temperature and feeding level on energy and protein metabolism of individually housed pregnant sows. In experiment 1, 12 pregnant animals were used. The stage of pregnancy at the start of the experiment ranged from 34 to 41 days. In experiment 2, 10 pregnant animals were used. The stage of pregnancy at the start of the experiment ranged from 38 to 47 days. In each experiment two groups of animals were used. Each group of five or six animals was individually tethered in one of two identical calorimeters and given one of two feeding levels. At the high feeding level the animals received about 1·35 × maintenance. At the low feeding level the animals received about 1·1 × maintenance. The temperature in experiment 1 changed stepwise in both calorimeters by 3°C every 5 to 7 days from 21 to 12°C and then in reverse order. Temperature in experiment 2 changed stepwise in both calorimeters by 2°C every 3·5 days from 25°C to 11°C and then in reverse order.
Energy gain was negative in animals at the low feeding level at the temperatures below 15 to 18°C. At the high feeding level sows lost energy at 12°C or lower in experiment 2. Protein gain was depressed by both low feeding level and low temperatures. Energy balance was depressed by about 90 kJ/kg M0·75 per day at the lower feeding level and by 19 kJ/kg M0·75 per day per °C below thermoneutrality. Protein gain was depressed by about 26 g/day at the low feeding level and by about 6 g/day per °C below thermoneutrality. Fat gain at low feeding level was depressed by about 92 g/day and by about 154 g/day at the lowest temperature. At low feeding level below the critical temperature, gain of fat was negative. Feeding levels used in these experiments did not supply sufficient energy for energy equilibrium or fat gain for the pregnant sow kept for longer periods below the thermoneutral zone.