Measurements of heat production(HP;
indirect calorimetry) and its partition between
maintenance, physical activity, thermoregulation,
and thermic effect of feed or energy gain were
carried out in sows maintained in different situations:
primiparous or multiparous; pregnant or nonpregnant;
thermoneutral or cold conditions; varied feeding levels;
and varied body weights (BW). Metabolizable
energy requirements for maintenance average 420 kJ/
kg BW.75 at thermoneutrality and moderate physical
activity. This value is not significantly affected by
parity, pregnancy, and stage of pregnancy. Physical
activity is a major factor causing differences in energy
balance between sows because activity is variable and
its energy cost (27 kJ·kg BW−.75·100 min−1 standing)
is four to five times higher than in other species.
Lower critical temperature (LCT) is approximately
20°C in pregnant and individually housed sows, and
daily HP is increased by approximately 15 kJ/kg
BW.75 for each degree Celsius decrease of ambient
temperature below LCT. Efficiencies of utilization of
ME for meeting energy requirements for maintenance,
maternal gain, and uterine gain are 77, 75, and 50%,
respectively. Equations for predicting energy deposition
in the uterus and mammary gland are proposed.
In addition to activity and thermoregulation, energy
requirements of pregnant sows depend on body
reserves of energy. Studies with newborn pigs indicate
that they are quite sensitive to ambient temperature
(i.e., +25 J·kg BW−.75·min−1 for each degree Celsius
decrease of temperature), and their LCT is 32 to 34°C.
The energy demand of pigs for thermoregulation just
after birth relies mainly on carbohydrates from
glycogen reserves or colostrum. Survival of newborn
pigs is highly dependent on the supply of colostrum