Induction of Ovulation and Fertility in Prepuberal Gilts

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Abstract
This study was conducted to evaluate fertility in 160 day-old gilts. In Experiment 1, 28 gilts in the following five groups were injected with (1) vehicle, (2) 500 µg of a synthetic gonadotropin releasing hormone (GnRH) analogue [D-Ala6-des-Gly-NH210] -LH-RH-ethylamide (AY 25205), (3) a combination 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 µg 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 µg 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 concentrations, all 51 gilts ovulated. Hormone treatment had no significant effect on the numbers of gilts detected in estrus, the ovulation rate (overall mean = 16.6), or the number of embryos. Ninety-five percent of the ova, based on the CL counts, were recovered from the oviducts of 20 gilts slaughtered 72 to 75 hr (Day 3) after the HCG or GnRH injections. Seventy-seven percent of the ova were fertilized, and all the gilts had some fertilized ova. Twenty of 31 gilts slaughtered on Day 30 were pregnant with an average of 9.7 normal embryos. Percentage embryonic survival based on the CL counts was 51.2%. Hormone treatment had no significant effect on the proportion of gilts pregnant or on the number of embryos. Of 11 gilts, that were not pregnant at slaughter, only three had been detected in estrus; of 20 gilts pregnant at slaughter, 19 had been detected in estrus. Non-pregnant gilts, compared to pregnant gilts, had significantly lower ovulation rates (8.0 vs 18.9, P<.01); lower body weights (87 vs 92.3 kg, P<.05); and lower plasma progesterone concentrations on Day 12 (29.4 vs 56.7 ng/ml, P<.01) and Day 15 (16.2 vs 42 ng/ml, P<.01). Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.