Concentrations of progesterone (P) in normal (CON) or nutrient-restricted (NR) gilts.

CON denotes normally fed gilts (2.86 kg/d) and NR denotes nutrient restricted gilts (1 kg/d). The day of the second occurrence of standing heat was designated as d 0. P, progesterone; E2, estradiol. * denotes P < 0.05. n = 10.