Gonadotrofina coriônica equina recombinante para indução de estro e ovulação em ovelhas lanadas

Abstract

Seasonality negatively impacts the intensification of production in sheep flocks. Alternatives to the use of purified equine chorionic gonadotropin (eCG) to induce follicular growth and ovulation in anestrus ewes have been explored but, so far, there is no treatment as efficient as purified eCG. In this study we aimed to compare purified eCG and recombinant eCG (reCG) on follicular dynamics, ovulation, luteal function, estrus and pregnancy in ewes during anestrus to transition period. In experiment 1, 27 adult ewes were used. On Day 0 (D0), the animals received an intravaginal device (IVD) containing 0.36g of progesterone, which was maintained for 7 days. On D7, all ewes received 250 µg of sodium cloprostenol IM and were randomly allocated into one of three groups: control (n=9), eCG (n=9), and reCG (n=9). The ewes did not receive any additional treatment in the control group, 400 IU of eCG in the eCG group, and 105 IU of reCG in the reCG group. Follicular diameter was assessed by transrectal ultrasonography at 24, 36, and 48 hours after the IVD removal. Ovulation was confirmed on D14 by the presence, area, and perfusion of the corpus luteum (CL). Luteal function was evaluated by blood perfusion of the CL using color Doppler and measured with ImageJ. Luteal function was assessed 7 and 12 days after IVD removal by serum P4 concentration. In experiment 2, 441 ewes (control = 117; eCG = 170; reCG = 154) were treated with a protocol similar to experiment 1, from early December to January, to assess estrus behavior and evaluate pregnancy and conception rates through natural mating. Pregnancy diagnosis was performed 25 to 30 days after ram removal. Data from experiment 1 were analyzed by ANOVA and Tukey's test. Ovulation, pregnancy, and estrus rates were evaluated using logistic regression and Fisher’s exact test. In experiment 1, the pre-ovulatory follicle size after 48 hours was greater (P<0.01) in the eCG group (5.22±0.23) and tended to be larger (P=0.052) in the reCG group (4.8±0.23) compared to the control group (3.98±0.23). The growth rate between the first (24h) and last (48h) evaluation was greater in the eCG (1.07±0.27) and reCG (1.05±0.27) groups compared to the control group (0.01±0.27) (P<0.05). The ovulation rate was higher in the eCG group (100%; 9/9) and reCG group (88.9%; 8/9) compared to the control group (0%; 0/0) (P<0.0001). There was no difference in the area and perfusion of the CL between treatments, but serum P4 concentrations were higher in the eCG group compared to the reCG and control groups; and higher in the reCG group compared to the control group on days 7 and 12. In experiment 2, ewes treated with eCG had a higher estrus rate (93.45%) compared to the control group (76.32%) (P<0.001), while the reCG group (87.58%) showed an intermediate result. Treatment with eCG or reCG did not affect pregnancy rates (P=0.73) or conception rates (P=0.75). During the transition to the breeding season, both reCG and eCG had a limited impact on pregnancy and conception rates through natural mating compared to P4+PGF treatment. However, during the anestrus period, reCG proves to be an alternative to purified eCG to promote follicular growth and induce ovulation.