**3.2 Proestrous P levels**

Plasma P levels increased gradually during proestrus, but did not show a distinct peak during the time window evaluated. Basal P levels defined by LH release characteristics showed no significant differences between groups and age did not affect P profiles (Table 1). Total P levels correlated significantly with basal P levels (r=0.876 with *P* < 0.001) and with P surge levels (r=0.992 with *P* < 0.001), in line with the observed elevation in P levels during the entire sampling period.
