Diferentes estratégias hormonais em protocolos de IATF sem a utilização de estrógeno na fertilidade de vacas

Abstract

In Brazil, synchronization protocols based on the association of progesterone (P4) with estradiol (E2) present satisfactory results in Bos indicus cows. However, E2 esters used in TAI protocols are banned in European countries and the United States. Furthermore, some countries in South America have prohibitions or restrictions regarding the use of E2 in cattle. In this context, the improvement of GnRH-based protocols, to obtain better results in Bos indicus cows, becomes necessary, if the restriction on E2 interferes the production and export of beef in Brazil. Thus, the objective was to evaluate the fertility of suckled Nelore cows, pre-synchronized with P4 and submitted to the ovulation synchronization protocol without the use of E2. In experiment 1[109 cows (study A) and 699 cows (study B)] 150 mg of injectable P4 (P4i) were administered ten days (D-10) before the TAI protocol. On D0, cows received an intravaginal P4 device and 2 mg of estradiol benzoate (EB; Control) or 20 μg of buserelin acetate (GnRH/EC and 2GnRH). Eight days later (D8), the P4 device was removed and all cows received 300 IU of eCG and 500 μg of cloprostenol sodium (PGF2α). Additionally, cows received 1 mg of estradiol cypionate (EC; Control and GnRH/EC) on D8 or 10 μg of buserelin acetate (2GnRH) on D10. Artificial insemination was performed on D10 (study B). In experiment 2 (699 cows), cows in the Control group underwent a TAI protocol similar to that of study B. Cows in the GnRH/EC, 2GnRH48 and 2GnRH54 groups were pre-synchronized with a P4 device seven days before the start of the TAI protocol (D-7) and received 200 μg of gonadorelin and an intravaginal P4 device on D0. The P4 devices were removed on D8 together with the administration of 300 IU of eCG and 530 μg of PGF2α. Furthermore, the GnRH/EC group received 1 mg EC and cows in the 2GnRH/48h and 2GnRH/54h groups were administered 100 μg GnRH 48 hours after removal of the P4 device. TAI was performed 48 hours (Control, GnRH/EC and 2GnRH/48h) or 54 hours (2GnRH/54h) after removal of the P4 device. Statistical analysis was performed by SAS. In study A, cows that received EC ovulated earlier (P=0.002) with no difference in the dispersion of ovulations (P=0.06). In all experiments, cows receiving GnRH on D0 had larger follicular diameter on D8 (Study A: P=0.002; Study B: P=0.001 and Exp. 2: P=0.001) and higher ovulation rate on D0 (Study A: P=0.002; Study B: P=0.001 and Exp. 2: P=0.001). In addition, estrus expression was higher in cows receiving EC (P=0.01; Study B and P = 0.001;Exp. 2). P/AI was similar between experimental groups in Study B (P = 0.19). However, P/AI was higher in the Control group (Exp. 2; P=0.001). In conclusion, estradiol removal (EC and EB) in ovulation synchronization protocols reduces fertility of lactating Bos indicus cows.