03088naa a2200313 a 450000100080000000500110000800800410001910000180006024501820007826000090026052021360026965000280240565000090243365000350244265000370247765000170251465000100253165000290254165000170257065000110258765000100259865000170260865300090262565300090263465300270264370000140267070000190268477300710270315196462023-05-18       1991    bl uuuu     u00u1 u    #d1 aEPPLESTON, J.  aEffect of time of PMSG and GnRH on the time of ovulation, LH secretion and reproductive performance after intrauterine insemination with frozen ram semen.h[electronic resource]  c1991  aAbstract: Two experiments were conducted in Merino ewes to investigate the effect of the time of pregnant mare serum gonadotrophin (PMSG) and gonadotrophin-releasing-hormone (GnRH) treatment on the time of ovulation and on the optimum time of insemination with frozen-thawed ram semen. In Experiment I. the time of oestrus, luteinizing hormone (LH) secretion and ovulation was determined in ewes following treatment with progestagen pessaries. In a factorial experiment, ewes were given PMSG at or 24 h before pessary removal (PR) and GnRH at 36 or 44 h after PR, or received no GnRH. Treatment with PMSG at ?24 h advanced the time of oestrus compared to controls (25/118 vs. 8/117 ewes marked 24 h after PR; P &lt 0.01) and advanced the time of ovulation (7/30 vs. 1/31 ewes ovulating by 50 h after PR; P &lt 0.05). GnRH treatment induced an LH peak within 1?4 h of treatment and reduced the period over which ovulation occurred from greater than 24 h in controls to 8?12 h and 12?24 h in ewes treated at 36 h and 44 h. In Experiment 2, two trials examined the effect of PMSG (at 24 h before PR) and GnRH treatment (Trial 1, nil vs. 36 h; Trial 2, nil vs. 36 vs. 44 h after PR) on fertility following insemination at SO or 65 h (Trial 1) or 48, 60 or 72 h (Trial 2). In both trials, individual ram (n = 14) affected fertility (range 30.3?79.6%; P &lt 0.01). In Trial 1, giving PMSG 24 h before PR and giving GnRH increased fertility (54.6% vs. 46.5%, P &lt 0.05; 57.8% vs. 43.3%, P &lt 0.001, for PMSG and GnRH treatment, respectively). The time of insemination was important in ewes treated with PMSG at PR only (37.0 ± 3.9% vs. 55.9 ± 3.9%; P &lt 0.01, following insemination at 50 h and 65 h. respectively). In Trial 2, neither PMSG nor GnRH treatment affected fertility, but the percentage of ewes pregnant was lower following insemination at 72 h (56.7%) than at 48 h (66.6%; P &lt 0.05) or 60 h (71.8%; P &lt 0.01). While the time of PMSG treatment advanced the time of ovulation, and treatment with GnRH resulted in a more synchronous ovulation, neither treatment variation provided a consistent improvement in fertility.  aArtificial insemination  aEwes  aGonadotropin-releasing hormone  aPregnant mare serum gonadotropin  aReproduction  aSheep  aInseminação Artificial  aLaparoscopia  aMerino  aOvino  aReprodução  aGnRH  aPMSG  aSincronizacao do estro1 aEVANS, G.1 aROBERTS, E. M.  tAnimal Reproduction Sciencegv. 26, n. 3/4, p. 227-237, Dec. 1991.