Inseminações sincronizadas com intervalo de 21 dias em novilhas Nelores não gestantes após diagnóstico precoce de gestação com ultrassonografia Doppler

Abstract

Two experiments were carried out to develop new strategies for resynchronization of ovulation in beef cattle. The first experiment was carried out in a commercial farm in Rio Branco-AC, using 300 Nellore heifers. After the first conventional TAI the heifers were distributed in two resynchronization programs with inseminations at intervals of 24 (PR-24) and 21 (PR-21) days. Treatments differed mainly at the time of resynchronization and at the time of the early preg check (PC) based in blood flow of the CL. In the PR-24, PC was at 22 days post TAI, non-pregnant heifers received an application of analog of PGF2α, estradiol cypionate, eCG and were inseminated on day 24. In the PR-21, the PC was on day 21, non pregnant heifers received gonadoreline and immediately after a new insemination was performed. Heifers of PR-21 had greater size of dominant follicle comparing with heifers of PR-24, 10.9mm (±1.9) vs. 10mm (±2.1), respectively (P=0.0003), but did not have difference in ovulation rate (86.9% PR-21 vs. 86.8% PR-24). The conception rate (CR) of the first TAI was 24.6%. The CR of resynchronized heifers was 33.6% and 29%, respectively, for PR-21 and PR-24 (P = 0.4). The CR of heifers that was false positive in the first PC was 21.6% and the pregnancy rates at the end of the breeding season for PR-21 and PR-24 were, respectively, 58.5% and 55.6%. There was a difference between resynch PR-21 + PR-24 CT compared to TAI (31% vs 24.6%; P = 0.01). It was observed a difference between bulls for conception 59.2% vs. 24.8% (P = 0.0001) and incidence of PC false positive 6.5% vs. 34% (P = 0.01). The second experiment was carried out in a commercial farm located in Valença-RJ with 76 Nellore heifers and the hormonal treatment was the same as were utilized in PR-21. The objective was to compare the efficacy of different methods of evaluation of the corpus luteum (vascular perfusion, size and ecotexture) in an objective way and in subjective scores with different evaluators, as a strategy of early PC at 21 days post TAI. Number of color pixels, ecotexture/mm² and diameter presented correlation of 0.65, 0.42 and 0.70, respectively, with the PC at 33 days (P<0.0001). Accuracy, sensitivity and negative predictive value (NPV) of CL diameter were similar to counting colored pixels. No difference was observed between the evaluators and all presented similar correlations of the scores with their respective objective values with high significance in the correlations (P <0.0001). Only vascularization scores had the same efficiency as the objective evaluation, however, size and echocardiographic scores together had an accuracy of 88%, similar to vascularization scores of 87.8%. The methodologies of subjective scores presented similar efficiency by the analysis in the ROC curve (P = 0.34). False positive PC was 22.7% and 19.2% (P = 0.3), while the false negative PC was 0% and 5.4% (P = 0.0001), respectively for PC in Doppler mode and B mode (echotexture + size). The PR-21 presented the same efficiency as PR-24 and Doppler ultrasound showed the same efficiency when used subjectively, while the CL size showed the same efficiency as the Doppler only objectively evaluated