Resumen

PORTILLO-MARTINEZ, Germán E; GUTIERREZ-ANEZ, Juan C  y  DE ONDIZ, Aitor D. Effect of the eCG Dose on Follicular and Luteal Characteristics, Ovulation Time and Ovulation Rate of Crossbred Zebu Heifers Synchronized with an Intravaginal Progestagen Device. Rev. Fac. Cienc. Vet. [online]. 2015, vol.56, n.1, pp.035-041. ISSN 0258-6576.

The effect of a reduced dose of eCG on follicular growth, luteal characteristics, ovulation time (OT) and ovulation rate (OR) was evaluated in crossbred Zebu heifers synchronized with an intravaginal progestagen device. A total of 41 cyclic heifers was selected and synchronized with an intravaginal sponge (IE) impregnated with 250 mg of medroxy-progesterone-acetate (MPA), using the following protocol. Day 0: insertion of IE plus 2 mg of estradiol benzoate (EB) im and 25 mg of PGF_2a im. Day 6: 12.5 mg de PGF_2a, 21 heifers received 400 IU eCG im (T1; n = 21) and 20 received 200 IU (T2; n = 20). Day 8: IE withdrawal. Day 9: 0.5 mg of BE im. Heifers were timed-artificial inseminated (TAI) between 52 and 56 h after IE withdrawal. Ultrasound evaluation was performed between d 6 until d 8, every 24 h, to determine the rate of follicular growth (FGR). Then, from d 8 until ovulation, heifers were evaluated every 8 h to determine diameter of the ovulatory follicle (DOF), OT, and diameter (CLD) and area (CLA) of the corpus luteum. The OR was also assessed. The variables FGR, DOF, CLD and CLA were analyzed using PROC GLM, while OT was analyzed using the NPAR1WAY procedure and OR using Chi-square with PROC FREQ from SAS.   No differences were found in FGR, DOF, and CLA (1.44±0.27 vs. 1.72±0.27 mm/d; 12.61±0.47 vs. 13.85±0.47 mm and 33.9±2.1 vs. 30.3±2.4 mm² for T1 and T2, respectively). Ovulations occurred at 61.67±1.8 h and 62.73±1.92 h, respectively, after IE withdrawal for T1 y T2, respectively. The CLD in T1 was higher (P<0.05) than T2 (21.7±1.44 vs. 16.9±1.56 mm). Higher OR (P=0.06) were found in T1 than in T2 (95.25 vs. 75.0%). In conclusion, the dose of 200 IU of eCG was sufficient to induce an suitable follicular growth without affecting OT and dosing with 400 IU of eCG improved the corpus luteum characteristics and allowed to obtain a greater number of ovulations in crossbred Zebu heifers synchronized with an intravaginal progestagen.

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