Comparación de dos protocolos de sincronización para IATF con semen sexado en vaconas Brown Swiss en condiciones subtropicales

The evaluation of reproductive indices is a key aspect of the livestock industry. Regardless of the animal biotype being used, it is essential to quantify reproductive efficiency in order to implement the necessary corrective actions. In the Amazon region of Ecuador, despite the existing edaphoclimatic constraints, the use of reproductive biotechnologies has made it possible to achieve favorable results. The present study aims to compare a J-Synch synchronization protocol, which reduces progesterone treatment to 6 days, extends proestrus, and involves insemination 72 hours after progesterone device removal, with a conventional protocol involving 7 days of progesterone device insertion and fixed-time artificial insemination (FTAI) 52 to 56 hours after progesterone device removal. For this purpose, 20 Brown Swiss Bos taurus heifers, approximately 2.25 years of age, with a live body weight of 453 ± 6 kg and a body condition score of 3.02, grazing Dallis grass (Brachiaria decumbens), were randomly assigned to two groups: conventional (n = 10) and J-Synch (n = 10). All heifers underwent artificial insemination (AI) using frozen-thawed, sex-sorted semen processed with SexedULTRA™ technology, containing 2.0 × 10⁶ viable cells per 0.25 mL straw, with X-chromosome-bearing spermatozoa and a sorting accuracy of >90%. Pregnancy diagnosis was performed 30 days after AI using transrectal ultrasonography. The data were analyzed using a general linear model, and the conception rate was treated as a dichotomous variable. The results showed an estrus expression rate of 73.5 ± 23.5% across all animals, although no statistically significant differences were observed between groups (P > 0.82). Slight numerical differences were observed in the diameters of the right and left preovulatory follicles between groups (14 ± 1.8 and 13 ± 2.4 mm, respectively; P > 0.73). The pregnancy rate per AI was higher with the J-Synch protocol (60%) compared with the conventional protocol (40%). Consequently, the overall pregnancy rate was 50% (10/20 animals). However, no statistically significant differences were observed when comparing pregnancy rates between the conventional and J-Synch protocols (P = 0.37). It is concluded that the J-Synch protocol resulted in higher absolute pregnancy rates than the conventional protocol across all replicates performed. Delaying the timing of AI using frozen-thawed, sex-sorted semen in Brown Swiss heifers under a 6-day progesterone J-Synch protocol improved pregnancy rates per AI.