Induction of ovulation and fertility in prepuberal gilts.

This study was conducted to evaluate fertili ty in 160 day-old gilts. In Experiment 1, 28 gilts in the following five groups were injected with (1) vehicle, (2) 500 /ag of a synthetic gonadotropin releasing hormone (GnRH) anal ogne [ D-Ala 6-des-Gly-NH2101 LH-RH-ethylamide (AY 25205), (3) a cbmbination of 400 IU of pregnant mares' serum gonadotropin and 200 IU of human chorionic gonadotropin (400 IU PMSG:200 IU HCG), (4) 1,000 IU of PMSG and (5) 1,000 IU of PMSG followed by 500/lg of GnRH analogue 72 hr later. In groups 1 to 5 the number of gilts treated, number of gilts ovulating and the mean +SE corpora lutea (CL) number were (1) 6, 0, 0; (2) 6, 3, .7 -+ .3; (3) 5, 5, 23.2 + 6.8; (4) 5, 4, 6.8 -+ 2.9; (5) 6, 6, 17.2 + 4.6. The CL number for group 3 was significantly greater than for group 4 (P<.05) but not group 5. The ovarian and uterine horn weights of gilts in groups 3, 4 and 5 were similar to each other and significantly greater than those for gilts in groups 1 and 2 (P<.05). None of the gilts in groups 1 or 2 were detected in estrus. In Experiment 2, injections of either 1,000 IU of PMSG or 400 IU PMSG: 200 IU HCG followed by either 500 IU of HCG or 500 ~tg of GnRH analogue were administered to 51 gilts. All gilts were artificially inseminated 30 hr after the second injection. Thirty-seven of 51 gilts (73%) were detected in estrus. Based on the presence of CL and plasma progesterone con-