416 EFFECTS OF THE CORPUS LUTEUM WITHIN THE OVARY ON THE FOLLICULAR DYNAMICS AFTER FOLLICULAR ASPIRATION AND ON THE DEVELOPMENTAL COMPETENCE OF ASPIRATED OOCYTES

Abstract

The use of ultrasound-guided transvaginal follicular aspiration combined with in vitro embryo production is increasing in the commercial cattle breeding industry. However, frequent puncture of follicles can induce the dysfunction of corpora lutea (CL) (Petyim et al. 2001 J. Vet. Med. A 48, 449–463), resulting in irregular estrous intervals or absence of estrus. This study was conducted to compare follicular and oocyte characteristics in ovaries ipsilateral vs. contralateral to the CL after follicular aspiration. The experiment was performed using a crossover design with each Japanese Black cow (n = 7) assigned to each of the 3 groups. The treatment period was 30 days for each group, and successive treatments were separated by a 2-month rest period. Hence the study spanned a period of 7 months (3 treatment periods and 2 rest periods). To verify ovulation prior to each treatment, the stage of the estrous cycle in each cow was synchronized with an ovulation synchronization (Ovsynch) program. Follicular aspirations were performed 6 times (every 3 or 4 days) between Day 3 and Day 20 after GnRH administration (Day = 0) of the Ovsynch program. All cows in each group ovulated the follicle before the initiation of follicular aspiration treatment. Follicles (e3 mm in diameter) from the ovary ipsilateral (Group 1) or contralateral (Group 2) to the CL were aspirated a using B-mode ultrasound scanner equipped with a 7.5 MHz probe. As a control (Group 3), the follicles from both ovaries were aspirated, irrespective of the presence of CL. In all groups, follicular development in each cow was monitored daily from Days 0 to 31. The cumulus–oocyte complexes (COCs) collected from each cow in Group 1 (n = 158), Group 2 (n = 140), and Group 3 (n = 277) were subjected to IVM/IVF/IVC. The numbers of embryos cleaved and developed to the blastocyst stage were recorded 3 days and 8 days after IVF, respectively. The mean profiles of total visible follicles (e3 mm in diameter) in ovaries with follicular aspiration in Groups 1 and 2 were similar to those in Group 3, irrespective of the presence of CL. The average numbers of visible follicles in the ovaries with follicular aspiration 7 days after the end of follicular aspiration treatment were not different from those in the ovaries without follicular aspiration (P > 0.05; one-way ANOVA). Moreover, there were no significant differences among the groups with respect to the percentages of cleavage (57.5–65.7%) and development to the blastocyst stage (23.6–32.1%) of collected COCs (P > 0.05; chi-square analysis). These results indicate that the presence of CL within the ovaries does not affect the ovarian follicular dynamics after follicular aspiration and the developmental competence of collected COCs.