Comparison of estradiol benzoate doses for resynchronization of ovulation at 14 days after timed-AI in suckled beef cows

• Published in: Theriogenology 2022-05, Vol.184, p.41-50
• Main Authors: Guimarães da Silva, Amanda, Nishimura, Thiago Kan, Rocha, Cecília Constantino, Motta, Igor Garcia, Laurindo Neto, Adomar, Ferraz, Priscila Assis, Bruni, Gabriela Andrade, Orlandi, Raphael Evangelista, Massoneto, João Paulo Martinelli, Pugliesi, Guilherme
• Format: Article
• Language: English
• Subjects: Animals; Beef cattle; Bos indicus; Cattle; Color-Doppler; Estradiol - analogs & derivatives; Estradiol - pharmacology; Estradiol benzoate; Estrus Synchronization - methods; Female; Follicular wave emergence; Insemination, Artificial - methods; Insemination, Artificial - veterinary; Ovulation; Pregnancy; Progesterone - pharmacology; Resynchronization protocol
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2022.02.025

We aimed to compare the effects of use of 1 or 2 mg estradiol benzoate (EB) associated with an intravaginal progesterone (P4) device for resynchronization of ovulation 14 days after timed-AI (TAI) in suckled beef cows. Nelore cows were submitted to a TAI (D0) and on D14, received an intravaginal P4 device and were randomly assigned to EB-1 group [n = 516] or EB-2 group [n = 510], which that received 1 or 2 mg EB, respectively. Also, cows had the ovaries scanned by ultrasound to detect an active CL on D14. On D22, devices were removed and structural luteolysis was detected by color-Doppler ultrasonography. In cows which underwent luteolysis, the resynchronization protocol was continued and they were submitted to second TAI on D24. Pregnancy diagnosis was performed 30–35 days after first or second TAI. A subgroup [n = 18–19/group] was submitted to daily ovarian ultrasound scanning from D14 to D22. Proportion of cows with an active CL on D14 did not differ (P > 0.1) between EB-1 and EB-2 groups. The proportion of cows with an active CL on D22 and pregnancy per AI (P/AI) at first TAI were greater (P ≤ 0.05) in EB-1 (55% and 51%) than in EB-2 group (48% and 42%). The P/AI at second TAI did not differ (P > 0.1) between EB-1 (47% [106/227]) and EB-2 group (42% [110/259]). Cumulative pregnancy rate was greater in EB-1 (73% [370/508]) than in EB-2 group (64% [322/502]). No difference (P > 0.1) was observed in the proportion of non-pregnant cows with a synchronized follicular wave emergence between EB-1 and EB-2 groups. In conclusion, treatment with either 1 or 2 mg EB associated with an intravaginal P4 device at D14 after TAI are efficient to synchronize a new follicular wave emergence. The decreased P/AI from first TAI observed in the group of cows receiving 2 mg indicates that this dose is not recommended for use in resynchronization programs initiated 14 days after TAI. The use of 1 mg EB associated with a P4 device provides an elevated cumulative pregnancy rate after two TAIs with an interval of 24 days. •Treatment with 1 or 2 mg estradiol benzoate (EB) and a P4 device at 14 days after TAI are efficient to synchronize follicular wave emergence.•Pregnancy establishment is impaired by use of 2 mg EB for resynchronization at 14 days after TAI.•The use of 1 mg EB is safer and results in improved pregnancy rates in the resynchronized cows after two TAIs.•Cows with low BCS have reduced presence of CL at resynchronization and increased early pregnancy loss.