Characteristics of the endogenous or pLH-enhanced
plasma LH surge are shown (Table 1). The onset of the
endogenous LH surge consistently preceded the onset of
standing estrus; ovulation occurred 39.4–45.4 h after the
defined onset of the natural or pLH-enhanced LH surge,
and 33.4 2.7 h after the peak of the natural or pLHenhanced
LH surge. Interestingly, exogenous pLH was
consistently given before the start of the endogenous LH
surge. There was no difference between treatments in the
duration of the LH surge. The maximum plasma pLH
concentration reached at the peak of the LH surge, as well
as the amplitude of the LH surge, were greater in pLHtreated
gilts than in the littermate controls (P = 0.01).
Evaluation of individual pLH profiles from littermate
pairs (Fig. 1A and B) revealed that the exogenous pLH
treatment consistently increased both peak plasma LH
concentrations and the amplitude of the LH surge.
Although pLH treatment did not affect onset of the LH
surge, variation in the interval between treatment and
the time peak LH was greater in saline-treated controls
than the pLH-treated gilts (P = 0.01).