Induction of puberty and maintenance of pregnancy in prepuberal gilts

The effects of estradiol benzoate (EB) and human chorionic gonadotrophin (HCG) on ovulation, fertilization, and maintenance of pregnancy were tested on 53 prepuberal gilts during the year 1978. In Experiment I, 8 gilts averaging 170 days of age were injected with 0.4 mg EB twice daily for 3 consecutive days. Human chorionic gonadotrophin was administered (500 i.u.) 36 hours after the last EB injection. Gilts were slaughtered either 31, 55, 77, or 100 hours after HCG injection. Only 39% of the follicles in 2 gilts had ovulated by 77 hours post HCG injection but 83% had ovulated in another gilt by 100 hours. In Experiment II, 15 gilts averaging 176 days of age were put on trial. Five of these gilts were injected in the same manner as in Experiment I and were maintained in the same pen with 5 gilts and 2 boars which had no hormone treatment. Five more gilts were kept in a pen away from the sight and sound of a boar. There was no difference in age settled between the gilts maintained in the same pen. Two gilts receiving hormone treatment returned to estrus 18 and 21 days after HCG injection and farrowed an average of 8 live pigs while three gilts with only boar exposure farrowed an average of 5 live pigs. In Experiment III, 30 gilts averaging 150 days of age were alloted equally to 1 of 3 treatments. Twenty gilts were injected with EB and HCG in the same manner as in Experiment I and 10 of these gilts were artificially inseminated 48 to 72 hours after HCG injection. The other 10 gilts were maintained in an adjacent lot and observed for estrus. Ten gilts were also maintained in a pen away from the sight and sound of a boar. Estradiol benzoate treated gilts experienced first estrus earlier (P < .01) than control gilts. Eight of the bred gilts returned to estrus at an average of 37.3 days post HCG injection. Four of these gilts were rebred to a boar and settled an average of 9.8 live feti past 80 days gestation. Progestin levels prior to the start of treatment were all below 1.5 ng/ml of plasma while at day 12 (HCG = day 0) of the induced cycle, progestin levels averaged 18.33 ng/ml (eliminating 3 gilts with levels below 1.5 ng/ml) for gilts receiving EB and HCG treatment. Progestin levels of the 4 gilts bred on the following estrus averaged 23.2 ng/ml on day 10.