143 IMPROVEMENT OF A SUPERSTIMULATORY PROTOCOL IN NELORE COWS: REPLACING THE LAST TWO DOSES OF pFSH BY eCG

In the present study, the superstimulatory protocol coined P-36 (Nogueira et al. 2007 Theriogenology 67, 655–660) was modified in order to test if replacement of pFSH by eCG in the last day of superstimulatory treatment would improve follicular growth, ovulation rate, and embryo yield. Nelore cows (n = 20) were randomly allocated to two groups: P-36/LH48 and P-36/LH48/eCG. Each female received both treatments in a cross-over design; the first experimental period was in October (Spring 2006, both groups) and the second in February (Summer 2007, both groups). At a random stage of the estrous cycle (D0), animals received a progesterone intravaginal device (DIB�, 1.0 g; Syntex S.A., Buenos Aires, Argentina) plus estradiol benzoate (EB, Estrogin�, 2.5 mg IM; Farmavet, Sao Paulo, Brazil). The animals were superstimulated with pFSH (Folltropin-V�, Bioniche Animal Health, Ontario, Canada), administered twice daily in decreasing doses of 53.2, 39.9, 26.6, and 13.3 mg (total dose = 133 mg), from Day 5 to Day 8, except the P-36/LH48/eCG group, where the last two doses of pFSH were replaced by two doses (200 IU) of eCG (Novormon�, Syntex, Buenos Aires, Argentina). All cows were treated with D-cloprostenol (150 µg IM;Veteglan�, Calier, Barcelona, Spain) on Day 7 at 7:00 h, and DIBs� were removed 36 h after PGF2alpha administration. On Day 9, ovulation was induced by pLH administration (Lutropin�, 12.5 mg IM; Bioniche Animal Health) at 7:00 h. The animals were inseminated at 12 and 24 h after pLH administration, without estrus detection. Embryos were recovered on Day 16 or 17. Data were analyzed by ANOVA (Proc Mixed, SAS; SAS Institute, Inc., Cary, NC, USA), and the difference was considered significant when P < 0.05 or not significant (NS). Results for animals from groups P-36/LH48 and P-36/LH48/eCG were compared and are reported in this order. The number of follicles with diameter larger than 6 mm at the time of pLH administration (15.25 � 2.06 and 21.05 � 2.76; P < 0.01), the ovulation rate observed up to 48 h after pLH administration (77.7 � 5.6 and 83.9 � 2.6; NS), the total number of oocytes/embryos recovered (6.65 � 1.18 and 10.0 � 1.48; P < 0.03), the number of embryos recovered (6.05 � 1.24 and 8.35 � 1.30; NS), and the number of viable embryos (5.10 � 1.10 and 7.30 � 1.20; NS) are reported. The embryo quality (excellent, good, fair, and poor) was NS among groups P-36/LH48 and P-36/LH48/eCG. It is concluded that replacement of pFSH by eCG, on the last day of the superstimulatory protocol P-36, was beneficial since there was a significant increase in the number of follicles (>6 mm at the time of pLH administration) and the total number of structures recovered. Experiments are in progress to confirm these beneficial effects of eCG on the P-36 protocol. This work was supported by FAPESP (Sao Paulo, Brazil). A. C. Z. Barcelos received a fellowship from CAPES (Brazil).