Veterinarija ir Zootechnika

This study aimed to determine selected reproductive parameters, including estrus synchronization response, pregnancy rate, and prolificacy, in Bulgarian local goats subjected to estrus synchronization and artificial insemination (AI) with frozen semen during the breeding season. The investigation was carried out on 101 lactating Bulgarian local goats during the breeding season. Estrus synchronization (ES) was performed using intravaginal sponges containing 60 mg medroxyprogesterone acetate for 14 days, followed by an intramuscular injection of 500 IU PMSG (pregnant mare serum gonadotropin) on the day of sponge removal. The response to synchronization was assessed based on changes in the vaginal appearance. A single artificial insemination with frozen semen was conducted 48–52 hours after sponge removal. Pregnancy diagnosis was performed on day 35 after AI. Based on ultrasound pregnancy diagnosis and kidding data, pregnancy rate (PR) and prolificacy were recorded. The registered estrus synchronization response, pregnancy rate, and prolificacy were 100%, 22.7%, and 108.6%, respectively. In conclusion, the applied estrus synchronization protocol and artificial insemination with frozen semen during the breeding season provided acceptable pregnancy rates and prolificacy in Bulgarian local goats, particularly when the primary objective is acceleration of genetic progress in the flock. Further investigations into factors affecting the success of these assisted reproductive technologies are necessary to improve their efficiency.

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.