Comparative efficacy of extended progesterone-based oestrus synchronisation protocols for fixed-time cervical artificial insemination in tropical crossbred goats

Optimization of oestrus synchronization protocols for artificial insemination in tropical goat production presents challenges, particularly with regard to limited understanding of extended progesterone procedures and alternative hormonal strategies suitable for resource-limited farming systems. This study evaluated four distinct synchronisation protocols in crossbred meat goats under tropical conditions in northeastern Thailand. A total of 210 crossbred multiparous does (25.0 ± 2.5 kg body weight) were randomly allocated to four treatments: SP13PM13PG13 (n=32, 13- day progesterone with PMSG/PGF2α at withdrawal), SP16PM14PG14 (n=64, 16-day progesterone with PMSG/PGF2α on day 14), CG16PM14PG14 (n=43, 16-day progesterone with PMSG/PGF2α on day 14), and CG17GnRH (n=71, 17-day progesterone with PGF2α on day 15 and GnRH on day 18). Does received intravaginal progesterone sponges (65 mg medroxyprogesterone acetate) followed by fixed-time cervical artificial insemination twice per protocol using frozen-thawed semen (0.25 ml, 150 × 10⁶ spermatozoa). Pregnancy diagnosis was performed ultrasonographically at 60 days post- insemination. Statistical analysis employed chi-square tests with Bonferroni correction. Overall conception rate was 40.5% (85/210). Protocol-specific conception rates were: CG16PM14PG14 53.5%, SP13PM13PG13 46.9%, SP16PM14PG14 37.5%, and CG17GnRH 32.4%, with no significant differences between treatments (P > 0.05). Oestrus response rates differed significantly (P < 0.001), with CG17GnRH showing reduced expression (49.3%) compared to others (79.7-87.5%). SP13PM13PG13 produced exclusively singleton births whilst other protocols achieved 43.5-60.9% twinning rates. Parity showed no effect on conception (P > 0.05). The findings indicate that multiple synchronization procedures result in equivalent fertility outcomes, permitting farmers to determine protocols based on economic and administrative factors rather than considered fertility advantages support the application of adaptable reproductive biotechnology for sustainable production of small ruminants in developing economies.