This study set out to investigate the efficiency of long-term estrus synchronization protocols and ovulatory follicle dynamics in ultrasonographically monitored Santa Inês ewes during lengthening (LD; September-October) and shortening photoperiods (SD; April-May), and the transitional period (TP; January). In addition, the influence of ovarian status (e.g., size of antral follicles and/or presence of corpora lutea-CL) at the outset of the estrus synchronization protocols on the ensuing development of ovulatory follicles was examined. Seventy sexually mature Santa Inês ewes were subjected to one of the two estrus synchronization regimens; on Day 0 (random day of the estrous cycle or anovulatory period), the ewes were fitted with an intravaginal progesterone-releasing (CIDR) device, which was left in place for 14 days (G-1CIDR, n=35) or replaced on Day 7 (G-2CIDR, n=35), and received an i.m. injection of 10 mg of PGF2α. The ewes allocated to the G-1CIDR group had mean serum progesterone (P4) concentrations <2 ng/mL during the last four days of the synchronization protocol. There were no differences (P>0.05) in mean ovulation rates between the two protocols tested nor among the ewes varying in ovarian status or studied at different times of the year, but ovulations occurred ∼12 h later in TP compared with the SD period (P<0.05). Ovulatory follicles emerged earlier (P<0.05) in the G-1CIDR than G-2CIDR group (Day 8.3±0.5 vs. 9.2±0.4) and during LD (Day 7.1±0.6) compared with TP (Day 9.1±0.6) and SD (Day 9.9±0.5 of the protocol). In conclusion, the replacement of CIDR devices prevented the occurrence of lower than normal luteal phase levels of P4 at the end of the 14-day estrus synchronization protocol. However, even though this procedure and seasonal influences altered certain growth characteristics of ovulatory follicles, there were no effects of these factors on the mean ovulation rate.