Animal Grouping and Ultrasonography
The study was conducted on 16- to 18-mo-old sexually mature, nulliparous, crossbred beef heifers (primarily Hereford). Heifers (n = 27) were maintained in a single corral and fed to gain approximately 1.3 kg weight per day. Ovarian follicle development was monitored daily by transrectal ultrasonography using a 7.5-MHz linear-array transducer (Aloka Co. Ltd., Tokyo, Japan). Ultrasound examinations commenced at least 2 days before the ovulation preceding the estrous cycle under study and continued until the day of ovariectomy in order to monitor the development of follicles > 4 mm in diameter. Topographic location and diameter of individually identified follicles and corpora lutea were recorded on a daily basis. ventolin 100 mcg
The day of wave emergence (Day 0) was determined retrospectively and defined as the day on which the dominant follicle of a wave was first detected at a diameter of 4-5 mm. The dominant follicle was defined as the largest follicle of a wave, and subordinate follicles were defined as those that appeared to originate from the same pool of follicles. As the heifers ovulated, they were randomly designated to be ovariectomized on Day 3 of wave 1 (D3W1, n = 8), Day 6 of wave 1 (D6W1, n = 6), Day 1 of wave 2 (D1W2; n = 1 on Day 9, 2 on Day 10, 2 on Day 11, 1 on Day 13 after ovulation), or in the immediate preovulatory period a 17 days after ovulation (Da 17, n = 2 on Day 17, 3 on Day 18, 1 on Day 19, 1 on Day 21 after ovulation).