Induction of estrus with intramuscular injections of GnRH or PMSG in lactating goats (Capra hircus ) primed with a progestagen during seasonal anestrus

In Experiment 1, goats in seasonal anestrus (n=154) were treated with sponges impregnated with 1 of 2 types of progestagen (MAP or FGA) followed by PMSG (400 IU im) 48 h before sponge removal. The type of progestagen used had no effect on kidding, abortion, pseudogestation, multiple births, stillbirths, number of live births per doe or gestation length. In Experiment 2, lactating goats (n=24) in seasonal anestrus were treated with progestagen sponges (MAP). At sponge removal they received one of the following treatments: 1 injection of PMSG (400 IU im), 1 injection of GnRH (125 mug im; GnRH-1), or 2 injections of GnRH (125 mug/injection im; GnRH-2) at a 48 h interval. Serum samples were taken at 6-h intervals for 96 h, starting 12 h after sponge removal. Heterologous radioimmunoassays were validated for the measurements of goat FSH, LH, E(2) and P(4). The onset of estrus (P=0.004), mean doe receptivity (P=0.0006), maximum preovulatory E(2) concentrations (P=0.0001) and LH peak concentrations (P=0.08) occurred significantly later for GnRH-1 and GnRH-2 than for PMSG treatment. The PMSG treatment induced a preovulatory LH peak in a greater number of goats (P=0.05) and gave a higher gestation rate than GnRH-1 and GnRH-2 treatments (57 vs 0 vs 12%; P=0.03). It is likely that the GnRH treatments administered did not reactivate the hypothalamo-pituitary-gonadal axis. Thus, intramuscular injections of GnRH in lactating goats primed with a progestagen were not as effective in regulating reproductive performance during seasonal anestrus as were injections of PMSG.