|Abstract or Summary
- Two experiments were conducted utilizing crossbred gilts to evaluate follicle characteristics at puberty and to determine the effect of exogenous estradio1-17β on embryonic mortality in the mature cycling gilt. Experiment 1 was conducted to compare preovulatory follicle numbers and sizes and follicular fluid concentrations of progesterone, estradio1-17β, plasminogen activator and plasmin in the same gilts (n=9) six hours after detected first and third estrus. Relationships between follicular fluid concentrations of steroids and those present in vena cava and ovarian venous blood were also examined at each estrus. Follicular fluid and serum concentrations of steroids were determined by use of radioimmunoassays and a caseinolytic assay was used to assess follicular fluid levels of plasminogen activator and plasmin. Total estrus) and third estrus. However, gilts at first estrus had more follicles 4-8 mm diameter (P<0.05) and 8.1-10 mm diameter (P<0.01) than at third estrus. Follicular fluid, ovarian venous sera and systemic sera concentrations of estradiol -17β were greater in gilts at third estrus than at first estrus (P<0.05). Follicular fluid concentrations of estradiol-17β in gilts at first and third estrus were positively correlated with concentrations of this steroid in ovarian venous sera (r=.51, r=.12, respectively) and systemic sera (r=.25, r=.80, respectively). Follicular levels of progesterone, plasminogen activator and plasmin and systemic serum levels of progesterone did not differ between gilts at first and third estrus. The lower follicular fluid concentration of estradiol -17β in gilts at puberty compared with that of the third estrus gilt may be attributed to differences in follicular development. The greater asynchrony in follicular development of gilts at puberty may be related to the reported increase in embryonic mortality that occurs in these animals. Experiment 2 was conducted to determine the effect of exogenous estradio1-17β on embryonic mortality in the mated third and fourth estrous gilt. Eight gilts were injected intramuscularly with 5 mg of estradio1-17β on the first day of detected third or fourth estrus. Control gilts (n=9) were similarly injected with vehicle only. All gilts were mated to fertile boars and slaughtered on days 30-32 of gestation. Fetuses were examined for viability, weighed and measured (crown-rump length). Treatment had no detrimental effect on fetal survival (control, 85.4% vs treatment, 83.3%) and did not affect weight or length of the fetuses. In treated and control gilts, fetal weight increased with age (r=.82, r=.66, respectively) as did fetal length (r=.79, r=.50, respectively). Exposing the oocyte or early developing embryo in the mature gilt to exogenous estradiol did not induce a greater incidence of embryonic mortality.