Lack of improvement on embryo production by the replacement of the last two doses of PFSH by ECG in superstimulated Nelore heifers.

Abstract

Results from a previous experiment have shown that the replacement of pFSH by eCG on the last day of the superstimulatory treatment in Nelore (Bos indicus) cows resulted in a greater superovulatory (SOV) response as compared to the treatment exclusively with pFSH (Barros CM et al. 2008 Repr. Fertil. Dev. 20, 152 abst). The aim of this study was to investigate if a similar approach would be beneficial for embryo production in nulliparous Nelore heifers. Forty heifers were randomly divided into two SOV groups: FSH Group: eight pFSH injections or FSH-eCG Group: six pFSH injections followed by two eCG injections. Each female received both treatments 65 days apart in a cross-over design. The SOV protocols consisted of an IM injection of 2 mg estradiol benzoate (Estrogin, Farmavet, S&#xe3;o Paulo, Brazil) and insertion of an intravaginal progesterone releasing device (1.9 g progesterone, CIDR, Pfizer, Hamilton, New Zealand) on Day 0. On Day 4.5, the superstimulatory treatments (70 mg pFSH; Folltropin-V, Bioniche Animal Health; Belleville, ON, Canada) were initiated and given in decreasing doses of 28, 21, 14, and 7 mg twice a day, over a 4-day period. The FSH-eCG Group had the last two doses of pFSH replaced by two doses of 150 IU eCG (Folligon, Bioniche). At the time of the fifth and sixth injections of FSH, 25 mg dinoprost tromethamine (Lutalyse, Pfizer, Paulinia, Brazil) was injected IM. The CIDR was removed at the time of the seventh superstimulatory injection. Ovulation was induced with an IM injection of 0.05 mg GnRH (gonadorelin acetate; Gestran Plus; ARSA S.R.L., Buenos Aires, Argentina) 12 h after the last superstimulatory injection. All heifers were artificially inseminated with frozen/thawed semen from the same bull 12 and 24 h after GnRH. Seven days after the first AI, embryos/ova were recovered using a nonsurgical uterine flushing technique and classified according to IETS standards. To determine the superstimulatory (number of follicles &ge;6 mm 12 h prior to GnRH) and SOV (number of ovulated follicles 48 h after GnRH, confirmed by CL number at the time of embryo collection) responses, transrectal ultrasonography was performed. Data were analyzed by paired t test and are presented as mean &#xb1; SEM. There was no difference between FSH and FSH-eCG groups regarding superstimulatory (23.2 &#xb1; 1.9 v. 22.3 &#xb1; 1.6 follicles &ge;6 mm, P = 0.56) or SOV (15.2 &#xb1; 1.1 v. 17.5 &#xb1; 1.4 CL, P = 0.21) responses. Treatments were also similar for number of total embryos/ova (9.6 &#xb1; 0.9 v. 9.5 &#xb1; 1.0, P = 0.91), viable embryos (4.9 &#xb1; 0.7 v. 3.7 &#xb1; 0.5, P = 0.17), or degenerate embryos (3.0 &#xb1; 0.6 v. 4.3 &#xb1; 0.7, P = 0.10) recovered. Contrasting with the results using Nelore cows, the present study did not observe improvement on embryo production by replacing of the last two doses of pFSH by eCG in superstimulated heifers.<fn-group><fn>Financial support from CNPq, FAPESP, EMBRAPA and Pfizer of Brazil.</fn></fn-group>