83 Response to follicle-stimulating hormone superstimulation in heifers with ovarian activity suppressed by active immunization against gonadotrophin-releasing hormone

Abstract

In the present study, we evaluated the ovarian response to exogenous FSH stimulation in the absence of endogenous LH, using as experimental model heifers immunized against GnRH. Pubertal, cycling Nelore (Bos indicus) heifers were allocated into three experimental groups: (1) non-immunized, FSH stimulated (B−FSH⁺, n = 5), (2) immunized, FSH stimulated (B+FSH⁺, n = 5), and (3) immunized, nonstimulated (B+FSH⁻, n = 5). Active immunization was obtained by 3 subcutaneous injections of 1.0 mL anti-gonadotrophin-releasing hormone vaccine (Bopriva, Zoetis), given at 20-day intervals. Effective immunization was characterised by the absence of growing follicles >4 mm or corpora lutea (CL) on the ovaries. Follicular wave emergence was synchronized in groups B+FSH⁺ and B+FSH⁻ by follicle ablation, and in group B−FSH⁺ by using of a protocol consisting of an injection of 2 mg of oestradiol benzoate and 0.5 mg of sodium cloprostenol, and insertion of an intravaginal progesterone (P4) device (1 g). Four days later (Day 0), groups B−FSH⁺ and B+FSH⁺ received 100 mg of NIH-FSH-P1 (Folltropin-V, Vetoquinol), injected twice-a-day in 8 decreasing doses, and group B+FSH⁻ received saline. Transvaginal ultrasonography (7.5 MHz) was performed daily from Days 0 to 4 and the number and size of follicles were recorded. P4 devices of group B-FSH⁺ were removed at Day 3. All heifers underwent ovum pickup (OPU) at Day 4, and the cumulus–oocyte complexes (COC) recovered were graded for quality. Viable COC were used for in vitro embryo production. The heifers were re-evaluated at Day 11 (7 days after OPU). The GLIMMIX procedure from SAS (SAS Institute Inc.) with repeated-measure statement was used to analyse the effects of group, day, and interactions; and the Chi-squared method was used to analyse binomial data. The results are shown as mean ± s.e.m. A progressive increase in average follicle size was observed in groups B−FSH⁺ and B+FSH⁺ (P < 0.0001), whereas no follicle growth was observed in group B+FSH⁻ (P > 0.05). Follicle growth rate was similar between groups B−FSH⁺ and B+FSH⁺, and both were greater than group B+FSH⁻ (1.2 ± 0.2 and 1.1 ± 0.1 vs. 0.0 ± 0.1 mm/d; P < 0.0001). However, the smaller follicle size in group B+FSH⁺ at Day 0 resulted in smaller follicle size at Day 4, compared with group B−FSH⁺ (2.4 ± 0.1 vs. 3.6 ± 0.2 and 6.9 ± 0.7 vs. 8.2 ± 0.6 mm, respectively; P < 0.05). There was no (P > 0.05) difference in the number of COC recovered among groups. The group B+FSH⁺ yielded fewer (P < 0.01) COC of grades I and II and more (P < 0.01) degenerated oocytes than groups B−FSH⁺ and B+FSH⁻ (41.2% vs. 80.0% and 68.0%, and 34.0% vs. 19.8 and 7.0%, respectively). Nevertheless, blastocyst rates were similar (P > 0.05) for B−FSH⁺, B+FSH⁺, and B+FSH⁻ (57.1%, 45.9% and 44.2%, respectively). Residual follicles or luteal tissue were observed after OPU only in group B−FSH⁺, resulting in a significant difference in the size of ovaries between Days 0 and 11, compared with that of groups B+FSH⁺ and B+FSH⁻ (3.7 ± 1.4 vs. 0.2 ± 0.2 and −0.2 ± 0.2 cm², respectively; P < 0.05). In summary, exogenous FSH supported follicle growth but did not improve oocyte quality in heifers immunized against GnRH.

This research was funded by CAPES.