277 FOLLICULAR GROWTH, SUBSEQUENT OVUM PICKUP, AND DOMINANT FOLLICLE REMOVAL IN COWS

Abstract

The present study was designed to assess the recruitment of follicles after ovum pickup (OPU) and dominant follicle (DF) removal on the follicular wave after OPU in Holstein dry cows. Cows were reared under the same feeding and environmental conditions. In Experiment 1, follicle aspiration (>2 mm in diameter) by OPU using a 7.5-MHz linear transducer with needle (COVA needle; Misawa Medical, Tokyo, Japan) connected to an ultrasound scanner (SSD-1200; ALOKA, Tokyo, Japan) was performed in four cows. Then, ovaries were observed after OPU from Day 1 (Day 0 = the day of OPU) to Day 11 to assess the number of follicles developed. In Experiment 2, two sessions of OPU were performed with a 7 day interval between sessions, with or without dominant follicle removal, to assess the quality of developing follicles and oocytes. In the DF removal group, >8-mm follicles were aspirated at Day 5 after the first OPU session, and the same cows without DF removal were designated as a control (n = 4, crossover trial). Oocytes were evaluated by their cumulus cell morphology, cytoplasmic color, and density. To assess the developmental competence of oocytes, Grades 1 and 2 cumulus-oocyte complexes (COCs) were collected, matured, fertilized, and cultured as described by Imai et al. (2002 J. Vet. Med. Sci. 64(10), 887-891). Embryo development was assessed by the cleavage rate on Day 2 and the blastocyst formation rate on Days 7 to 9 (the day of insemination = Day 0). Data were analyzed by ANOVA or Student t-test. In Experiment 1, a dominant follicle (>8 mm in diameter) was developed during Days 3 to 5 after OPU in each donor. The mean number of developing follicles (>2 mm in diameter) were increased from Day 1 to Day 9 (Day 1: 7.5 ± 2.1, Day 3: 19.0 ± 1.2, Day 5: 23.3 ± 9.0, Day 7: 30.3 ± 11.0, Day 9: 42.0 ± 15.8 and Day 11: 41.0 ± 16.7 (mean ± SD), P < 0.05). In Experiment 2, there was no difference in the mean number of developing follicles on the day of OPU and collected oocytes between DF removal and control groups (follicles: 47.8 ± 23.0 and 39.3 ± 6.2; oocytes: 27.0 ± 11.6 and 26.5 ± 5.4, respectively). The number of Grades 1 and 2 oocytes for the DF removal group was significantly higher (P < 0.05) than that for the control (83.6 ± 1.5 and 63.2 ± 14.2, respectively), and no significant difference was found within cleavage (60.0 ± 37.2, 53.6 ± 23.2) and blastocyst rates (34.1 ± 33.9, 34.4 ± 16.8). These results indicate that populations of follicles were increased till Day 9 after OPU, and the DF removal was effective at increasing oocyte quality in the developing follicles.