Fuente: PubMed "nature biotechnology" Theriogenology. 2025 Dec 12;252:117784. doi: 10.1016/j.theriogenology.2025.117784. Online ahead of print.ABSTRACTThe aim of this study was to evaluate the use of buserelin acetate, a GnRH analog, in combination with estradiol benzoate (EB) at the beginning of an early resynchronization protocol (R22) in Bos taurus beef heifers. A total of 656 heifers underwent a first fixed-time artificial insemination (FTAI; designated as D0) and received a reused intravaginal progesterone (P4; 1 g) device on D22. At that time, heifers were randomized into two treatment groups: EB (1 mg; n = 329) or GnRH + EB (1 mg of EB plus 10 μg of buserelin acetate; n = 327). On D30, the P4 device was removed, and a pregnancy diagnosis was performed. Non-pregnant heifers (EB = 152/329; GnRH + EB = 134/327) received 200 IU of equine chorionic gonadotropin, 1 mg of estradiol cypionate and 0.5 mg of cloprostenol sodium, followed by a second FTAI on D32. A subset of heifers underwent ovarian ultrasonography on D22 (n = 463), D30 (n = 193), and D32 (n = 165); a second pregnancy diagnosis was performed on D62. Heifers treated with EB alone had larger dominant follicles on both D30 and D32 (P = 0.0001) and a higher incidence of early ovulation before FTAI compared to GnRH + EB group (18.9 % vs. 8.8 %; P = 0.03). The GnRH + EB group achieved a superior pregnancy rate at R22 (EB = 40.8 % vs. GnRH + EB = 56.0 %; P = 0.008) and a higher cumulative pregnancy rate (EB = 68.4 % vs. GnRH + EB = 79.2 %; P = 0.01). In conclusion, the administration of 10 μg of buserelin acetate combined with 1 mg of EB at the beginning of the R22 protocol improved conception rates in Bos taurus beef heifers.PMID:41397337 | DOI:10.1016/j.theriogenology.2025.117784