Efeito da progesterona e da prostaglandina em vacas nelore (Bos indicus) submetidas à IATF

Abstract

The present study was performed in three experiments: 1 (effect of progesterone on conception rate), 2 (effect of early luteolysis on follicular dynamics) and 3 (effect of early luteolysis on conception rate). In experiment 1 were used in 1006 Nelore cows (Bos indicus) distributed into four treatments according to category (lactating x nonlactating cyclic) and the device number of uses (new x previously used for 8 days) in a 2x2 factorial design. At the insertion of the P4 device (D0), all animals received 2mg of oestradiol benzoate (EB). In eight days (D8) all cows were treated with 25 mg of PGF2α plus 1 mg of estradiol cypionate (EC) and 300UI eCG. Conception rates were 152/294 (51.7%) for lactacting/new; 189/363 (52.1%) for nursing/used; 51/151 (33.8%) for nonlactating/new and 91/198 (46.0%) for nonlactating/used (P = 0.0007). In experiment 2 (n=44) was evaluated the effect of early PGF2α/ luteolysis at progesterone-based protocol on follicular dynamics and P4 perfil in cycling nonlactating Nelore cows. Three treatments were performed: PGF D0/8, D6 and D8). Thus, in D0/8 treatment cows were treated with 25mg of PGF at device insertion and withdrawal; PGF D6, PGF administered at 48h before device withdrawal; and D8, PGF administered only at device withdrawal. At device withdrawal (D8) all cows were treated with 300UI of eCG and 1mg of EC. To device insertion from withdrawal, follicular dynamics was monitored by ultrasonography every 24 hours. To D9 from 96 hours after device withdrawal the ultrasound exam was performed at 12h intervals. To evaluate P4 profile, blood samples were collected on D0, D3, D6, D7, D8, D9, D10 and D22. The D0/8 treatment was significantly better than D6 and D8 for the DF daily growth rate to device insertion from withdrawal (1.1±0.1 vs 0.9±0.1 vs 0.8±0.1mm/day, respectively), SF diameter (4.9±0.3 vs 4.0±0.2 vs 4.1±0.2mm), DF diameter (6.6±0.2 vs 5.7±0.1 vs 5.9±0.2mm). The maximum diameter of DF and the ovulation rate (TxOV) were lower in D8 treatment (8.1±0.7mm and 35.5±13.3%) when compared to D0/8 and D6 treatments which showed no differences between them (9.9±0.3 vs 9.7±0.4mm and 93.3±6.7 vs 80.0±10.7%, respectively). In summary, the early luteolysis inducted the more expressive development of dominant follicle due to lower circulating P4 during the protocol. In experiment 3 (n=342), was performed the same experimental design of experiment 2 to evaluate the conception rates to timed artificial insemination (TAI). Ultrasound examination was performed in 20% of females and in 99% (99/100) was found corpus luteum (cyclic females). The conception rate of D0/8, D6 and D8 treatments was similar (59.3% vs 63.4% vs 60.6%, respectively, P> 0.05). Thus, we conclude that the decrease in blood levels of exogenous/endogenous progesterone during the synchronization protocol enhances follicular growth and ovulation, and may be an alternative to optimize TAI programs.