Induction of ovulation in the prepuberal gilt by pulsatile administration of gonadotropin releasing hormone

An attempt was made to induce precocious puberty in gilts approximately 164 days of age by stimulating a luteinizing hormone (LH) secretory pattern similar to that which occurs before normal onset of puberty. Hourly iv administration of 1 μg synthetic gonadotropin releasing hormone (GnRH) for 7 or 8 days resulted in a mean serum LH concentration of 1.7 ± .3 ng/ml in three treated gilts compared with .9 ± .1 ng/ml in three control gilts (P<.08). Serum LH peak frequency was also greater (P<.05) in treated (3.4 ± .5 peaks/4 hr) than in control gilts (1.2 ± .1 peaks/4 hr), but serum LH peak amplitude was not altered (P>.33) by GnRH treatment. All treated gilts displayed estrus and ovulated within 6 days after treatment began, and all control gilts remained prepuberal throughout the study (P=.05). Only one of the three treated gilts displayed a normal estrous cycle and reovulated after treatment. Precocious ovulation but not puberty was induced in gilts by hourly administration of 1 μg synthetic GnRH, indicating that the pituitary and ovaries of 164-day-old gilts are competent and that final sexual maturation occurs at the hypothalamic level.