Reproductive efficiency of Nelore (Bos indicus) cows submitted to conventional resynchronization or ReBreed21
Mirela Balistrieri1, Tainá L P Azevedo1, Paula R Cortat1
1Department of Animal Science, Luiz de Queiroz College of Agriculture, University of São Paulo (ESALQ/USP), Piracicaba, SP, 13418-900, Brazil.
Theriogenology
|January 28, 2026
Summary
The ReBreed21 program improved pregnancy rates and reduced false positives in Nelore cows compared to conventional methods. Estradiol cypionate dose did not significantly impact fertility outcomes in this study.
Area of Science:
- Reproductive biology
- Animal science
- Veterinary medicine
Background:
- Optimizing reproductive efficiency in Nelore (Bos indicus) cows is crucial for beef production.
- Timed artificial insemination (TAI) programs are widely used, but resynchronization strategies can further enhance outcomes.
- Evaluating novel resynchronization protocols like ReBreed21 is essential for improving herd fertility.
Purpose of the Study:
- To assess the reproductive efficiency of Nelore cows using resynchronization programs for TAI.
- To determine the impact of different estradiol cypionate (EC) doses (0.5 vs. 1.0 mg) within the ReBreed21 program on reproductive parameters.
- To compare the ReBreed21 program with a conventional resynchronization strategy (Resynch33).
Main Methods:
- A total of 917 Nelore cows (253 primiparous, 645 multiparous) were assigned to Resynch33, ReBreed21 with 0.5 mg EC (REB0.5), or ReBreed21 with 1.0 mg EC (REB1.0).
- All cows underwent an initial synchronization protocol for TAI. ReBreed21 treatments involved a progesterone (P4) device, equine chorionic gonadotropin (eCG), and EC administration.
- Pregnancy diagnosis was performed using ultrasonography with color Doppler. Non-pregnant cows were re-inseminated, and pregnancy outcomes (pregnancy per AI, false positives, pregnancy loss) were monitored.
Main Results:
- The ReBreed21 program significantly increased pregnancy rates (PR) after 21 days of the breeding season (75.4-77.7%) compared to Resynch33 (52.8%).
- Time to pregnancy was shorter in ReBreed21 groups (8.5-10.8 days) than in the Resynch33 group (15.8 days).
- The incidence of false positives was lower in ReBreed21 (7.5%) compared to Resynch33 (13.7%), with no significant differences in pregnancy loss.
Conclusions:
- The ReBreed21 program effectively enhances reproductive efficiency in Nelore cows by anticipating pregnancies and improving overall PR.
- The ReBreed21 protocol demonstrated a significant advantage over the conventional Resynch33 strategy in terms of early PR and reduced false positives.
- The dose of estradiol cypionate (0.5 vs. 1.0 mg) did not influence key fertility parameters within the ReBreed21 program.
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