was 1,005 kJ/kg BW0.6·d–1. Therefor

was 1,005 kJ/kg BW0.6·d–1. Therefore, the feeding levels
of 60, 80, and 100% of their estimated ad libitum ME
intake (i.e., 1.44, 1.92, and 2.40 MJ ME/kg BW0.6·d–1)
were assumed to be above the maintenance requirement,
whereas the feeding levels of 0, 20, and 40% of their
estimated ad libitum ME intake were assumed to be below
the maintenance requirement. Feed allowance were
adjusted every 2 or 3 d based on mean anticipated BW
of the pigs. Within each growing phase, measurements
were conducted on 6 pigs per feeding level. An adaptation
period of 5 d was used to adjust to the new feeding
level. Barrows in the fasted treatment were fed on
an ad libitum basis during the adaptation period. After
the adaptation period, barrows in the fasted treatment
were kept in respiration chambers for 2 d to measure
FHP. Barrows assigned to the other treatments were
kept individually in open-circuit respiration chambers
for a 5-d balance trial followed by a 2-d fasting period.
Heat production in the fed state was measured and feces
and urine were collected in the balance trial. Diets were
based on corn and soybean meal (Table 1) and were formulated
to meet the nutrient requirements for growingafter cold performic acid oxidation overnight and hydrolyzed
with 7.5 mol/L HCl for 24 h at 110°C using
an amino acid analyzer (Hitachi L-8800; Hitachi, Ltd.).
Tryptophan was determined after LiOH hydrolysis for
22 h at 110°C using HPLC (Agilent 1200 Series; Agilent
Technologies Inc., Santa Clara, CA). The GE concentration
was measured using an adiabatic bomb calorimeter
(Parr 6300 Calorimeter; Parr Instrument Company,
Moline, IL). Samples of feces were analyzed for DM,
N, and GE. Samples of urine were analyzed for N using
fresh material. The concentration of GE in urine samples
was measured after 4 mL of sample were dripped into
2 filter papers in a special crucible and dried for 8 h at
65°C in a drying oven, and then the energy content was
determined using an adiabatic bomb calorimeter.