Effects of follicular status at treatment on follicular development and ovulation in response to FSH in Spanish Merino ewes
1999
López Sebastián, Antonio | González De Bulnes, Antonio | Santiago Moreno, Julián | Gómez-Brunet, A. | Townsend, E. C. | Inskeep, E. K. | López Sebastián, Antonio [0000-0001-8695-7441] | González De Bulnes, Antonio [0000-0002-0917-4475] | Santiago Moreno, Julián [0000-0001-5551-8120]
Cyclic Spanish Merino ewes were treated on Day 13 of the estrous cycle with 12 mg, im, FSH-P in saline (n = 9) or propylene glycol (n = 24), currently with 100 μg, im, Cloprostenol (Day 0). >From Day -6 to Day 0, the ewes were observed daily by transrectal ultrasonography, after Day 0, ultrasonography was performed every 12 h for 72 h. Sizes and locations of 1/2 mm follicles were recorded at each observation. The ovulation rate was determined by laparoscopy on Day 7 after estrus. The number of ovulations ranged from 0 to 6 in ewes treated with FSH-P in saline and from 0 to 16 in ewes receiving FSH-P in propylene glycol (P < 0.05). In the latter group, the response was bimodally distributed; about half of the females had 1 ovulation, whereas the remainder had >4 with a mean of 7 ovulations. The ovulation rate was associated with 2 characteristics of the largest follicle present at treatment (Day 0). First, if the largest follicle on Day 0 had not changed in diameter from Day -1 to Day 0, then 7 of 9 ewes had >3 ovulations; if the largest follicle had either increased or decreased, only 8 of 24 ewes had >3 ovulations (P < 0.05). Second, there was a linear trend (P < 0.07) for ovulation rate to decrease as the persistence of the largest follicle at treatment increased; no ewe in which the largest follicle on Day 0 remained present for more than 36 h ovulated more than 6 follicles. As with the ovulation rate, the numbers of large follicles on Day 1.5, 2 and 2.5 varied with the interaction of change in diameter of the largest follicle on Day 0 from Day -1 to Day 0 and with vehicle. In summary, the superovulatory response was affected by the change in diameter from Day -1 to Day 0 of the largest follicle on Day 0 and the period required for that follicle to regress after treatment with FSH-P and cloprostenol.
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