Veterinarija ir Zootechnika

The current study aimed to determine the reproductive performance and progesterone profile in East Friesian sheep after GnRH administration on day 4 post artificial insemination (AI). The experiment was carried out with 67 sheep subjected to estrus synchronization and artificial insemination. The animals were divided in two groups: I (control group, n = 30) and II (GnRH group, n = 37), treated by GnRH on day 4 after AI. Rams were introduced on day 12 and removed on day 20 after AI. Ultrasound pregnancy check was on days 20 and 60 after AI, and sheep were separated on the basis of their reproductive status (RS). Blood progesterone (P4) concentrations were measured by ELFA on days 4, 12 and 20 after AI, and a likehood for early embryonic mortality was estimated. The percentages of non-pregnant and pregnant sheep in both groups on day 20 were close; however, there were significantly (P < 0.05) more pregnant sheep in the GnRH group on day 60 compared with day 20. The investigated factors affected the P4 concentrations independently of each other. Analysis of the main effects of GnRH and RS showed a significant (P < 0.005) influence on the progesterone profile. The day after AI had a strong positive effect on the P4 concentration, with significant (P < 0.001) differences between mean P4 values measured during the different days. The estimated likehoods of early embryonic mortality (EEM) for both groups was 25.4%. In conclusion, GnRH injection on day 4 after artificial insemination and the introduction of ram on day 12 did not have a direct effect on the pregnancy rate, but led to improvement of the reproductive performance at the flock level. Gonadotropin releasing hormone treatment, reproductive status and day after AI affected the progesterone concentrations in East Friesian sheep irrespective of each other, and had a significant (P < 0.005) effect on the hormonal profile. The treatment by GnRH on day 4 after AI tended to reduce early embryo mortality, but future investigations are needed to clarify this effect.