Two experiments were designed to artificially alter the follicular wave pattern in calves to determine if the mechanisms controlling the well-ordered pattern of follicular growth in adults are extant in prepubertal animals as well. Experiment 1 was designed to test the hypothesis that follicle ablation in a random group of calves will induce synchronous emergence of a new follicular wave which is not different from a spontaneous wave. Experiment 2 was designed to test the hypothesis that ovarian superstimulatory response in calves is enhanced when treatment is initiated before rather than after the time of selection of the dominant follicle. In Experiment 1, 6-month-old calves were assigned randomly to an ablation group (n = 10) and a control group (no ablation, n = 10). Follicle ablation was accomplished by transvaginal ultrasound-guided needle aspiration of all follicles > or = 4 mm in diameter. Blood samples were taken and ovarian changes were monitored daily. A rise (P < 0.01) in mean plasma FSH concentration was detected 24 h after follicle ablation (1.51 ng/ml in the ablation group and 0.93 ng/ml in the control group). Wave emergence was detected earlier (P < 0.01) and with less variation (P < 0.0001) in the ablation group than the control group (1.2 +/- 0.1 vs 4.0 +/- 0.7 d). Characteristics of the induced wave were not different from those of the spontaneous wave. In Experiment 2, 7-month-old calves were assigned randomly to a pre-selection group in which superstimulation treatment was initiated at the time of wave emergence (1 d after follicle ablation, n = 11), or to a post-selection group in which superstimulation treatment was initiated after selection of a dominant follicle (4 d after follicle ablation, n = 11). Superstimulation treatment consisted of 30 mg of FSH im twice daily for 3 d. Ultrasound-guided transvaginal follicle ablation was used to synchronize follicle wave emergence at the outset of the experiment. The mean diameter of the largest follicle at the start of superstimulation treatment was 3.2 versus 8.5 mm in the pre- and post-selection groups, respectively (P < 0.001). The day after the last treatment, the number of follicles > or = 3 mm in diameter was greater (P < 0.002) in the pre-selection group than in the post-selection group (19.3 +/- 1.7 versus 11.3 +/- 1.3). In summary, ultrasound-guided follicle ablation resulted in synchronous wave emergence in a random group of calves, and superstimulation treatment initiated at the time of wave emergence (pre-selection group) resulted in the growth of more follicles than treatment initiated later (post-selection group). Mechanisms involved in the control of follicle recruitment, selection, and suppression are extant in calves, similar to those found in adults.