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Effect of time of PMSG and GnRH on the time of ovulation, LH secretion and reproductive performance after intrauterine insemination with frozen ram semen

1991; Elsevier BV; Volume: 26; Issue: 3-4 Linguagem: Inglês

10.1016/0378-4320(91)90049-6

1873-2232

J Eppleston, G. Evans, Emma Roberts,

Genetic and phenotypic traits in livestock

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 < 0.01) and advanced the time of ovulation (7/30 vs. 1/31 ewes ovulating by 50 h after PR; P < 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 < 0.01). In Trial 1, giving PMSG 24 h before PR and giving GnRH increased fertility (54.6% vs. 46.5%, P < 0.05; 57.8% vs. 43.3%, P < 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 < 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 < 0.05) or 60 h (71.8%; P < 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.