Effect of presence of a dominant follicle on the superovulatory response in Buffalo (Bubalus bubalis)

Ten buffalo were superovulated by administration of 8 doses of FSH in a descending schedule spread over 4 d (5.5/5.5, 4.5/4.5, 3.5/3.5 and 2.5/2.5 mL, im; total dose of 64 AU in 32 mL) beginning on Day 10 of an unstimulated estrous cycle, and 30 and 20 mg Lutalyse was given along with the 5th and 6th injections of FSH, respectively, to induce luteolysis. The number of corpora lutea (CL) was determined on 6 d post estrus. The ovaries were examined daily by ultrasonography from Day -5 to Day 5 (Day 0 = day of start of superovulation). The animals were retrospectively classified into 2 groups depending upon the presence (n=4) or absence of a dominant follicle (n=6). The mean diameter of the largest follicle (F1) increased from 8.25 +/- 0.48 mm on Day -5 to 10.75 +/- 0.25 mm on Day 0 in the dominant group, whereas in the nondominant group the F1 follicle exhibited a progressive decrease from 9.00 +/- 0.45 mm to 7.00 +/- 0.65 mm during the same period, the difference in profiles between the 2 groups was significant (P=0.042). The profile of the diameter of the second largest follicle (F2) and the difference in diameters between largest and second largest follicles (F1-F2) were not significantly different between the 2 groups. The profile of mean number of large (greater than or equal to 10 mm diameter), but not small (2 to 5 mm diameter) or medium (6 to 9 mm diameter) follicles differed significantly (P=0.001) between the 2 groups from Day -5 to Day 5 (P=0.030). The number of CL was not significantly different between nondominant (4.00 +/- 0.97) and dominant groups (3.25 +/- 1.31). The number of CL was positively correlated (P<0.01) with the number of medium follicles and the total number of follicles on the day of initiation of superovulation, but not with follicles of any size category or total number of follicles on any previous day. The results of this study indicate that following the use of morphological criteria based on the size of the largest follicle alone, the superovulation response is not affected by the presence of a dominant follicle at the initiation of superovulation in buffalo.