OVARIAN SYNCHRONIZATION FOLLOWING ULTRASOUND-GUIDED TRANSVAGINAL FOLLICLE ABLATION IN HEIFERS

In Experiments 1 and 2, ultrasound-guided transvaginal follicle aspiration was used as a method of follicle ablation to induce and synchronize subsequent follicular wave emergence and enhance ovulation synchrony following PGF(2 alpha) administration. Heifers were at unknown stages of the estrous cycle at the start of both experiments in which all follicles greater than or equal to 5 mm in diameter were ablated; luteolysis was induced 4 d later with cloprostenol (500 ug/dose, im). In Experiment 1, heifers were randomly assigned to either an ablation (n=17) or a procedural control (no follicle ablation, n=17) group. Ablation-induced wave emergence was indicated by a significant increase in the total number of follicles greater than or equal to 5 mm within 2 d of ablation (mean, 1.5 d), which was preceded by a significant surge in circulating FSH. Although the mean (+/-SEM) interval from PGF(2 alpha) administration to ovulation did not differ between follicle-ablated heifers (5.1+/-0.5 d; range, 3 to 9 d) and control heifers (5.9+/-1.0 d; range, 1 to 5 d), the variability of the interval was different (P<0.05). Inequality of variance between the 2 groups was attributed to a greater (P<0.08) degree of ovulation synchrony in the ablation group than in the control group; 13/16 (81%) versus 9/17 (53%), respectively, ovulated within 5 d of cloprostenol administration. Relative asynchrony of ovulations in control heifers was associated with the status of the follicular wave at the time of PGF(2 alpha)( administration and, in part, to incomplete luteolysis following a single dose of PGF(2 alpha). Experiment 2 was designed to examine the efficacy of 2 doses of cloprostenol 12 h apart (n=7) versus a single dose (n=8) to induce complete luteolysis subsequent to follicle ablation-induced wave emergence. Two doses of cloprostenol potentiated ovulation synchrony; more (P<0.05) 2-dose heifers (7/7, 100%) than single-dose heifers (4/8, 50%) ovulated within 5 d after PGF(2 alpha) administration. In summary, ultrasound-guided transvaginal follicle ablation, done at random during the estrous cycle, induced and synchronized subsequent follicular wave emergence, and resulted in a high degree of ovulation synchrony among heifers after PGF(2 alpha) induced luteolysis, especially when 2 doses of PGF(2 alpha), were administered 12 h apart.