OVARIAN SYNCHRONIZATION FOLLOWING ULTRASOUND-GUIDED TRANSVAGINAL FOLLICLE ABLATION IN HEIFERS

In Experiments 1 and 2, ultrasound-guided transvaginal follicle aspira tion was used as a method of follicle ablation to induce and synchroni ze subsequent follicular wave emergence and enhance ovulation synchron y following PGF(2 alpha) administration. Heifers were at unknown stage s of the estrous cycle at the start of both experiments in which all f ollicles greater than or equal to 5 mm in diameter were ablated; luteo lysis was induced 4 d later with cloprostenol (500 ug/dose, im). In Ex periment 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 h eifers (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 t han in the control group; 13/16 (81%) versus 9/17 (53%), respectively, ovulated within 5 d of cloprostenol administration. Relative asynchro ny of ovulations in control heifers was associated with the status of the follicular wave at the time of PGF(2 alpha)( administration and, i n part, to incomplete luteolysis following a single dose of PGF(2 alph a). Experiment 2 was designed to examine the efficacy of 2 doses of cl oprostenol 12 h apart (n=7) versus a single dose (n=8) to induce compl ete 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%) ovu lated within 5 d after PGF(2 alpha) administration. In summary, ultras ound-guided transvaginal follicle ablation, done at random during the estrous cycle, induced and synchronized subsequent follicular wave eme rgence, and resulted in a high degree of ovulation synchrony among hei fers after PGF(2 alpha) induced luteolysis, especially when 2 doses of PGF(2 alpha), were administered 12 h apart.