Exposição à progesterona antes do início do protocolo de sincronização da ovulação para TETF em receptoras zebuínas

Abstract

The aim of this study was to evaluate the effect of exposure to progesterone (P4) ten days before the start of the ovulation synchronization protocol for fixed-time embryo transfer (ET) on reproductive parameters of zebu recipients. Therefore, on a random day of the estrous cycle, ten days before the beginning of the (ET) protocol (D-10), 192 bovine recipients (62 heifers, 49 postpartum multiparous and 81 single multiparous) were randomly assigned to two experimental groups: control (n=96) and P4i (n=96), the latter receiving 150mg of P4 injected intramuscularly (i.m), when the ultrasound examination was performed to assess the presence of corpus luteum (CL) in all females. On D0, all animals were submitted to an ovulation synchronization protocol based on estrogen (E2) + P4 for ET. On D18, a new B-mode and Doppler ultrasound examination was performed on all recipients to determine the ovulation rate (TxOV) and on one sample (n=99) to measure the diameter (DCL), total area (ACL) and area of vascularization (AVASCL) of the CL. Still on D18, 160 recipients received a grade one embryo via the transcervical route. Pregnancy diagnosis was performed 23 days after TE and at 60 days to detect pregnancy losses. Statistical data were processed through descriptive analysis, Student's t test and Chi-square, considering a significance level of 5%. On D-10, 87.50% (168/192) of recipients had CL. TxOV [control 87.50% (86/96) and P4i 91.70% (88/96); P>0.05], DCL [control (1.82±0.32cm) and P4i (1.86±0.34cm); P>0.05], ACL [control (2.62±0.87cm²) and P4i (2.66±0.87cm²); P>0.05], AVASCL [control (0.52±0.27cm²) and P4i (0.53±0.20cm²); P>0.05]. The pregnancy rate at 30 days (TxP30) [control 44.73% (34/76) and P4i 52.38% (44/84); P>0.05], pregnancy rate at 60 days (TxP60) [control 40.80% (31/76) and P4i 46.42% (39/84); P>0.05], pregnancy loss [control 8.82% (3/34) and P4i 11.40% (5/44)]; P>0.05]. It is concluded that, under the conditions of this experiment, P4 before the ET protocol was not able to improve luteal development and fertility of zebu recipients.