Buserelina em protocolos de inseminação artificial em tempo fixo em ovinos

Abstract

The addition of buserelin in fixed-time artificial insemination (FTAI) may increase synchrony of ovulations and pregnancy rate. To test this hypothesis, three experiments were conducted using 445 ewes during the reproductive season (March and April). In all experiments, animals remained with a progestogen-impregnated vaginal device (PIVD) for seven days and received 250 µg of luteolytic agent (cloprostenol) at the time of PIVD removal (day 7 = D7). On D9 (54 h after PIVD withdrawal), ewes underwent superficial cervical FTAI using 100 x 106 motile sperm from a semen pool from four rams with known fertility. In Exp. 1, on D7, ewes (n = 30) were allocated in three groups: eCG (200 IU at PIVD removal; n=10); eCG+GnRH (200 IU eCG at PIVD removal and 4 µg buserelin 36 h later; n=10); or GnRH (buserelin 36 h after DIV removal; n=10). Blood samples were collected 2, 6, and 12 days after FTAI (54 h after PIVD removal) for analysis of serum P4 levels. In Exp. 2, also on D7, ewes were allocated to two treatments: eCG (n = 45) 200 IU of eCG at PIVD removal; or GnRH (n = 40) 4 µg of buserelin at FTAI. In Exp. 3, at D7, animals were randomly assigned to two treatments: eCG (n = 183) 200 IU of eCG; and eCG-GnRH (n = 147) 200 IU of eCG at D7 and 4 µg of buserelin at the time of FTAI. Pregnancy was diagnosed by transrectal ultrasonography 24 days after FTAI. Pregnancy data were analyzed by chi-square test. Serum progesterone levels data were analyzed using mixed models for repeated data. For both, p≤0.05 was considered significant, In Exp. 1, there was no significant effect of group (p=0.66) or group x day (p=0.24) on P4 concentration, and a significant effect was observed only for collection day (p=0.001). In Exp 2, the pregnancy rate was lower (p<0.05) in the GnRH group than in the eCG group. In Exp 3, the pregnancy rate increased (P=0.05) from 40.7% to 50.3% when eCG-GnRH was used. The results indicate improved pregnancy rate with buserelin treatment at the time of FTAI when eCG is administered at PIVD withdrawal. The use of buserelin alone at the time of FTAI does not replace treatment with eCG. Serum progesterone levels is not different after treatment with eCG, eCG+GnRH or GnRH.