title: Effects of season and ovarian status on the outcome of long-term progesterone-based estrus synchronization protocols and ovulatory follicle development in Santa Inês ewes under subtropical conditions.
abstract: 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) 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 (P4)-releasing (controlled intrauterine drug release [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 intramuscular injection of 10 mg of PGF2α. The ewes allocated to the G-1CIDR group had mean serum P4 concentrations less than 2 ng/mL during the last 4 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 hours later in the TP compared with the SD period (P < 0.05). Ovulatory follicles emerged earlier (P < 0.05) in the G-1CIDR group than in the G-2CIDR group (Day 8.3 ± 0.5 vs. 9.2 ± 0.4) and during LD (Day 7.1 ± 0.6) compared with the 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, although this procedure and seasonal influences altered certain growth characteristics of ovulatory follicles, there were no effects of these factors on the mean ovulation rate.
authors.affiliation: Department of Preventative Veterinary Medicine and Animal Reproduction, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil. Electronic address: m.emiliafraoli@fcav.unesp.br.
authors.forename: M E F
authors.initials: ME
authors.lastname: Oliveira
authors.affiliation: Department of Preventative Veterinary Medicine and Animal Reproduction, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil.
authors.forename: H
authors.initials: H
authors.lastname: Ayres
authors.affiliation: Department of Clinical and Veterinary Surgery, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil.
authors.forename: L G
authors.initials: LG
authors.lastname: Oliveira
authors.affiliation: Department of Preventative Veterinary Medicine and Animal Reproduction, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil.
authors.forename: F F P C
authors.initials: FF
authors.lastname: Barros
authors.affiliation: Department of Animal Reproduction and Veterinary Radiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University, Botucatu, São Paulo, Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Oba
authors.affiliation: Department of Animal Reproduction and Veterinary Radiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University, Botucatu, São Paulo, Brazil.
authors.forename: S D
authors.initials: SD
authors.lastname: Bicudo
authors.affiliation: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors.forename: P M
authors.initials: PM
authors.lastname: Bartlewski
authors.affiliation: Brazilian Agricultural Research Corporation-Embrapa Goats and Sheep, Coronel Pacheco, Minas Gerais, Brazil.
authors.forename: J F
authors.initials: JF
authors.lastname: Fonseca
authors.affiliation: Department of Preventative Veterinary Medicine and Animal Reproduction, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal, São Paulo, Brazil.
authors.forename: W R R
authors.initials: WR
authors.lastname: Vicente
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002980:Climate; D003338:Corpus Luteum / Q000000981:diagnostic imaging; D015237:Dinoprost / Q000008:administration & dosage; D030762:Estrous Cycle; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D006080:Ovarian Follicle / Q000254:growth & development*; D010053:Ovary / Q000000981:diagnostic imaging / Q000502:physiology*; D017440:Photoperiod; D011374:Progesterone / Q000008:administration & dosage* / Q000097:blood; D012621:Seasons; D012756:Sheep / Q000502:physiology*; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D015237:Dinoprost
keywords: Estrus synchronization; Ewe; Ovulatory follicle; Progesterone; Ultrasonography