Dinâmica folicular de vacas de corte tratadas com três protocolos de sincronização da ovulação

Background: Artificial insemination is an established and viable technique to accelerate the genetic advancement and economic return of the cattle. However, compromises the efficiency of detection of estrus results in low insemination rates. To avoid these problems in beef herd, synchronization protocols have been developed that allow inseminate large number of animals within a set period of time. These treatments are known as protocols for synchronization of ovulation for fixed-time artificial insemination (FTAI). There are several slow-release progesterone or progestins devices on the market for use in synchronization of estrus/ovulation programs in cattle, but these devices have a high cost, which results in less use of these protocols by farmers . This study aimed to determine the follicular dynamic of a low cost protocol to synchronize ovulation, which uses vaginal sponges impregnated with medroxy-progesterone acetate (MPA; group 1) and compare it with two trade protocols (groups 2 and 3). Materials, Methods & Results: Nine Braford cows, multiparous non-lactating, cyclic and BCS > 3 (BCS = 1 extremely lean cows and BCS = 5 obese cows) where used in these trial. The animals were divided into three treatments, which all animals went for three treatments in four replicates. Group 1 (n = 14), animals received on day 0, a vaginal sponge impregnated with 250 mg MPA and an intramuscular (i.m.) application of 2 mg of estradiol benzoate (EB); on day 8, the vaginal sponge was removed and applied i.m. 0.5 mg cloprostenol and 24 h latter was applied i.m. 1 mg of EB. Group 2 (n = 7), the animals received on day 0, a silicone vaginal implant with 1 g of progesterone and an application i.m. of 2 mg of EB; on day 8, the implant was removed and applied i.m. 0.5 mg cloprostenol and 24 h latter was applied i.m. 1 mg of EB. Group 3 (n = 8), the animals received on day 0, a silicone ear implant impregnated with 3 mg norgestomet and an application i.m. of 3 mg norgestomet and 5 mg of estradiol valerate; on the 9th day the implant was removed. From day 0, animals were examined daily by trans-rectal ultrasound with an 8 MHz linear transducer to monitor follicular and luteal dynamics. After removal of the implant in group 3 and after application of 1 mg EB in the other groups, the animals were evaluated by ultrasound two times per day until ovulation was detected. In group 1, seven animals lost a vaginal sponge impregnated with MPA and the data were removed from analysis. The emergence of follicular wave for groups 1, 2 and 3 occurred, respectively, 3.7 ± 1.1, 3.7 ± 0.7 and 4.9 ± 1.1 days, with a statistical trend (P < 0.06) to occur earlier in groups 1 and 2 than in group 3. There was no statistical difference between groups in other variables. The interval between wave emergence and ovulation occurred in 7.4 ± 0.9, 7.3 ± 0.7 and 7.6 ± 1.3 days (P = 0.82); the interval between implant removal and ovulation occurred in 66 ± 12, 66 ± 0 and 70.5 ± 12.7 hours (P = 0.62); the dominant follicle diameter at implant removal was 10.9 ± 2.6, 12.7 ± 2.1 and 10.3 ± 2.1 mm (P = 0.13); and the larger diameter of the dominant follicle was 15.3 ± 2.9, 16.6 ± 1.3 and 15.9 ± 1.5 mm (P = 0.49) for groups 1, 2 and 3 respectively. Discussion: In this experiment, the protocols used in groups 1, 2 and 3 were effective in promoting the emergence of a synchronized new follicular wave and promote synchronized ovulation of a follicle with few days of dominance and an appropriate diameter. It was observed that numerical variations on the emergence of the new follicular wave numerically influenced in the timing ovulations. A study with a larger number of animals per group should be performed to confirm these differences between the groups.