Abstract
Two studies were conducted to determine if postpartum (PP) reproductive function could be enhanced in ewes by PGF 2α during mid-gestation (Trial 1) and GnRH within 10 days PP (Trial 2). Trial 1 utilized 31 ewes (x̄ body weight = 84 kg) assigned to two treatment groups to receive (I.M.) either saline (control, n = 17) or PGF 2α (0.14 mg/kg body weight, n = 14) on day 74 of gestation. Results from the first study indicated success in regressing the corpus luteum (CL) of pregnancy as indicated by decreased serum progesterone (P 4, P < 0.05) by 24 hours after treatment. In addition, by 20 days after treatment, serum luteinizing hormone (LH) concentrations in treated ewes were higher ( P < 0.01) than in controls. However, ovarian activity was not re-established by 30 days PP in this study. In Trial 2, 35 ewes (x̄ body weight = 79 kg) were randomly assigned to one of four groups: no treatment (controls, n = 9), PGF 2α (no GnRH, n = 9), GnRH (no PGF 2α n = 9) or both PGF 2α and GnRH (n = 9). The PGF 2α-treated animals received 0.14 mg PGF 2α/kg body weight (I.M.) on day 73 of gestation and GnRH-treated ewes received 50 μg GnRH (I.M.) on days 2, 6, and 10 PP. As in Trial 1, P 4 concentrations in PGF 2α-treated ewes were lower ( P < 0.02) than in control ewes by 24 hours after treatment. Progesterone remained lower in PGF 2α-treated animals through day 116 of gestation. However, no differences were detected ( P > 0.65) in LH concentrations between the two groups in this same period. Likewise, no differences were observed ( P > 0.32) in LH concentrations between the PGF 2α-treated and control ewes on days 2, 6, and 10 PP. However, elevated ( P < 0.07) LH concentrations were noted in ewes receiving 50 μg GnRH compared with ewes not receiving GnRH. In addition, area under the LH curve (AUC) was greater ( P < 0.01) for GnRH-treated animals on days 2, 6, and 10 PP and LH AUC increased over the PP period in GnRH-treated ewes. Three of eight ewes receiving both PGF 2α and GnRH treatments had ovarian activity within 30 days PP as indicated by P 4 concentrations above 1 ng/ml while no other ewes had ovarian activity during this time period.
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