Ultrasound-guided follicular puncture (OPU) has become the most used technique to recover cumulus-oocyte complexes (COCs) from valuable donors for in vitro embryo production, because of the low risk and the possibility of collecting COCs at intervals as short as twice-a-week. However, repeated aspiration of ovarian follicles may induce endocrine abnormalities due to partial luteinization of punctured follicles and interference with follicular development. The use of exogenous progestagens is an alternative used to control these side effects, and is under evaluation. The aim of this study was to evaluate whether the effect of norgestomet treatment on intra-follicular and systemic steroid concentrations and on ovarian follicular dynamics is related to changes in LH releasing pattern. Pluriparous non-lactating Gir breed (Bos indicus) cows (n = 10) were randomly distributed between treatment (norgestomet ear implants, replaced weekly) and control (no hormone used) groups, and had their ovarian follicles larger than 3 mm in diameter aspirated twice a week, during the next two consecutive weeks. Follicular dynamics were evaluated every 12 h between OPU sessions, and the largest follicles present were used to recover samples of follicular fluid. Blood samples were collected daily for progesterone evaluation in all cows, and 3 times within a 4-h window interval, at 24, 48, 72, and 96 h after follicle puncture for LH evaluation, in 6 cows (3 from treated and 3 from control groups). LH was measured by a standardized RIA procedure. Data was analyzed by ANOVA, and means were compared by Tukey's test. Results are presented as means ± SEM. Treatment with norgestomet reduced mean progesterone plasma concentration during the evaluated period (36.3 ± 14.0 vs. 250.3 ± 49.3 pg/mL; P < 0.0001), the incidence of follicles growing above 9 mm (30% vs. 65%; P < 0.05) in the intervals between OPU sessions, and intrafollicular estradiol and progesterone concentrations in the largest follicles (n = 27) present (265.5 ± 47.4 and 34.9 ± 5.4 ng/mL vs. 765.2 ± 169.1 and 173.3 ± 43.4 ng/mL, respectively; P < 0.05). Plasma LH concentrations were consistently lower during the 3 session intervals in cows treated with norgestomet (0.16 ± 0.04, 0.22 ± 0.03, 0.22 ± 0.09 and 0.17 ± 0.01 vs. 0.44 ± 0.15, 0.53 ± 0.04, 0.42 ± 0.05 and 0.39 ± 0.11 for 24, 48, 72, and 96 h after OPU, respectively; P < 0.05). These results confirm the theory that norgestomet treatment is associated with a reduction in the LH-release pattern, as expected due to the reduction in both luteinization of punctured follicles and in the steroidogenic activity of growing follicles observed during the experiment. The use of norgestomet ear implants can be an alternative in the management of donor cows undergoing oocyte pickup.

This work was sponsored by FAPEMIG and CNPq. The authors thank Dr. Robert Douglas for aiding with LH RIA.