Pregnancy rate of Nelore cows submitted to resynchronization starting 14 or 22 days after prior FTAI

The objective of this study was to evaluate the pregnancy rate of cows resynchronized 14 vs 22 days after FTAI. In this study (experiment 1), 244 lactating Nelore cows receiving the first FTAI (Day 0) were submitted to two resynchronization programs Resync-14 Group (BCS = 3.0; N = 118) and Resync-22 Group (BCS = 3.0, N = 126). In the Resync-14 Group at day 14 was conducted insertion of intravaginal progesterone device (DP4) associated to the treatment with 100 mg injectable P4 (Afisterone, HertapeCalier). On day 22, the pregnancy diagnosis (PD) was conducted by CL functionality, using the ultrasound Collor Doppler mode (Mindray M5Vet, DPS Brazil). Cows that had CL with low or absence of blood flow were considered as pregnant. These animals had the DP4 removed and 150 μg of D-cloprostenol (VeteglanLuteolitico, HertapeCalier), 1 mg EC (cypionate HC, HertapeCalier) and 300 IU of eCG were administrated. The FTAI was performed 48 hours after DP4 removal (Day 24). The cows that were considered pregnant by the Collor Doppler pregnancy diagnosis were evaluated 8 days after to measure the amount of false positives. In the Resync-22 Group the insertion of DP4 was conducted at day 22, followed by administration of 2 mg of EB (HC benzoate, HertapeCalier). On day 30 the DP4 was removed, and PD was performed by ultrasound B-mode (Myndray, M5 VET, DPS Brazil). Animals with negative PD were treated with 150 g of Dcloprostenol (VeteglanLuteolitico, HertapeCalier), 1 mg of EC i.m. (HC cypionate, HertapeCalier) and 300 IU eCG i.m. (Folligon®, MSD Animal Health). The FTAI was performed 48 hours after DP4 removal. In experiment 2, it was evaluated the pregnancy rate of resynchronized cows 14 days prior FTAI. A total of 448 lactating Nellore and Crossbred cows (1/2 Nelore vs Angus; BCS = 3), was synchronized and inseminated at fixed time (Day 0). On day 14 the animals received the same methodology used in the Resync-14 Group and they were inseminated at fixed time on Day 24. Statistical analyzes were performed using PROC GLIMIX SAS 9.3. In experiment 1, no difference was observed between Resync-14 and Ressinch-22 groups (P u003e 0.05), respectively: conception rate to first FTAI (53 vs 48%), conception rate to resynchronization (51 vs 56%) and cumulative pregnancy rate in 24 (75% - 89/118) and 32 (77% - 97/126) days of the breeding season. The percentage of false positives in the pregnancy diagnosis at 22 days was 4.55%. In experiment 2, the conception rate to first FTAI, conception rate to resynchronization and the cumulative pregnancy rate was 49%, 51%, 75% respectively. These results suggest that the FTAI resynchronization program every 24 days can be used widely and effectively in beef cattle farms.