111 Use of gonadotrophin-releasing hormone (GnRH) or equine and human chorionic gonadotrophins for oestrus synchronization and their influence on embryo viability and progesterone levels on day 16 and 30 of goats receiving GnRH 5 days after intrauterine insemination or natural service

Abstract

Gonadotrophin-releasing hormone (GnRH) or equine and human chorionic gonadotrophins (eCG and hCG) were evaluated for oestrus/ovulation synchronization (E/OS), as well as the influence of GnRH 5 days post-breeding (dpb) on embryo viability (EV), and progesterone (P4) levels on Day 16 and 30 after laparoscopic AI (LAI) or natural service (NS). Fifty-four lactating/non-lactating Alpine breed goats (average of 3.82±1.2s.d. years of age) of mixed parity were E/OS during the early transitional breeding phase using 12±1 day of 300mg of P4 and 2mL of prostaglandin F2α analogue given at P4 removal. The experiment included a sub-group from a larger study in which a completely randomised design was used. The germane data were arranged as a 2×2×2 factorial. This study focused on goats receiving 120IU of eCG and 60IU of hCG (n=40), or GnRH analogue (n=14) 24h after P4 removal. At 5 dpb, 25 goats received 1mL (IM) of GnRH and the control (n=29) received 1mL of physiologic saline. Goats were time-bred 48h after P4 withdrawal by LAI (n=33) or NS (n=21). Pregnancy was diagnosed at 18 to 24, 30, and 40 dpb by non-return to oestrus, pregnancy-specific protein B, and ultrasound, respectively. EV was evaluated as the difference between pregnancy diagnosis results. Blood serum P4 was evaluated at 5, 16, and 30 dpb. A logistic regression model was used for statistical analysis. Pregnancy rate (PR) for LAI or NS, at 18–24, 30, and 40 days was 73 vs. 76%, 67 vs. 62%, and 64 vs. 67%, respectively (P>0.72). In contrast, when GnRH was used for E/OS, the 5 dpb GnRH influenced EV at 30 days (95 vs. 81%; P=0.06) but not at 40 days (89 vs. 86%; P>0.35), compared with placebo. Similarly, with the exception of PR at 40 days (43 vs. 72%; P=0.05), for the GnRH and eCG/hCG E/OS groups, respectively, PR was not affected (P>0.12) by either E/OS or GnRH 5 dpb or their interaction (P>0.35) at any pregnancy diagnosis (i.e. 18–24, 30, or 40 dpb). Likewise, levels of P4 at 5, 16, and 30 dpb did not affect PR at 18–24, 30, and 40 dpb (P>0.92, 0.71, and 0.11). As shown in Table 1, the level of P4 was not influenced for goats receiving GnRH or placebo at 5, 16, or 30 dpb. The baseline mean P4 blood serum level for goats receiving GnRH 5 dpb differed at 16 but not at 30 dpb (P<0.001). Table 1 Blood serum progesterone (P4, ng mL−1) in response to gonadotrophin-releasing hormone (GnRH) or placebo given 5 days post-breeding Sampling day GnRH Placebo P >1 Mean ±SE Mean ±SE 5 (baseline) 6.2a 0.83 5.7a 0.72 0.66 16 11.7b 1.11 11.0b 1.05 0.65 30 6.2a 0.89 7.6c 0.84 0.26 a–cMean values with different superscripts within a column signify statistical difference for GnRH (P<0.001) and placebo (P<0.02). 1Probability for mean differences in the same row.