Comparative efficacy of CIDR and intravaginal sponge synchronization with reduced sperm doses for laparoscopic artificial insemination in tropical goat production.

Fixed-time laparoscopic artificial insemination (FT-LAI) using frozen-thawed semen can accelerate genetic improvement in goats, but its efficiency depends on appropriate ovulation synchrony and effective use of cryopreserved spermatozoa. Controlled internal drug release (CIDR) devices and intravaginal fluorogestone acetate sponges are widely used progestogen-based synchronisation tools. However, their comparative performance under tropical field conditions, particularly when reduced sperm doses are used for LAI, remains insufficiently defined. A 2 × 2 factorial field trial was conducted in 175 multiparous Boer × Thai native does to compare synchronisation method (CIDR vs. intravaginal sponge) and insemination dose (150 × 106 vs. 60 × 106 progressively motile spermatozoa). Does received a 13-day intravaginal progestogen treatment followed by 250 IU eCG at device removal, and FT-LAI was performed during the expected periovulatory period. Pregnancy diagnosis was conducted by transrectal ultrasonography at Day 42 post-insemination. Follicular size and ovulatory status were assessed laparoscopically at insemination. CIDR-treated does had a higher pregnancy rate than sponge-treated does (76.1% vs. 59.0%; p = 0.024; OR = 2.21, 95% CI: 1.15-4.22). Sperm dose did not significantly affect pregnancy rate (150 × 106 (72.1%) vs 60 × 106 (65.4%), p = 0.452; OR = 1.36, 95% CI: 0.70-2.64). The interaction between synchronisation method and sperm dose was not significant. Laparoscopic observation at insemination showed that the CIDR-treated group had a higher proportion of does with recent ovulation (33.8% vs. 3.6%; p < 0.0001) and slightly larger right ovarian follicles (6.15 ± 1.41 vs. 5.80 ± 1.21 mm; p = 0.00054). These findings indicate that CIDR-based synchronisation yields greater follicular readiness at insemination and higher early pregnancy outcomes compared with sponges, while using the lower sperm dose did not significantly reduce Day 42 pregnancy rates under the present study conditions. The protocol has potential practical relevance for improving genetic resource use in tropical goat production systems.