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OVULATION SYNCHRONIZATION PROTOCOLS AND FACTORS ASSOCIATED WITH PREGNANCY RATE OF ZEBU FEMALES

Background. Fixed time artificial insemination is an important tool for the reproductive management of cattle. Objective. To determine the effect of two ovulation synchronization protocols and factors associated with the pregnancy rate of Zebu females using fixed time artificial insemination (FTAI) under tropical conditions. Methodology. Data of estrous and pregnancy from 129 multiparous Zebu cows and 257 heifers were used. All animals received an intravaginal device (new or used) CIDR® or DIB®, which remained in situ per 7 days. On the day of device removal, two treatments were established. I) Estradiol cypionate (EC; n = 192): 25 mg prostaglandin F2 alpha and 0.5 mg EC (estradiol cypionate); II) Estradiol benzoate (BE; n = 194): 25 mg PGF2α and 24 hours later (day 8), 1 mg BE. Estrous was detected by 1-hour; three times a day, and females inseminated 54-56 hours after removal of device, using thawed semen. Pregnancy diagnosis was by transrectal palpation with real-time ultrasound, 60 days after FTAI. Data were analyzed using Chi-square tests. Results. The overall estrous rate was 73.32%. The ovulation synchronization protocol affected the presence of estrous, where EC had a higher rate (79.39%) compared to EB (67.19%). Pregnancy rate for the females inseminated with thawed semen was 54.40%. All factors affected the pregnancy rate (p<0.05). Implications. This study provides an alternative for increasing estrous and pregnancy rate of Zebu females, using EC synchronization protocol. It also shows that female type, device and BCS change influence pregnancy rate. Conclusion. The highest rate was observed in heifers showing estrous, synchronized with a new intravaginal device, using EC and gaining body condition score.