Potential role for GnRH in the synchronization of follicular emergence before the superovulatory Day 0 protocol.
The ability of gonadotropin-releasing hormone (GnRH) to synchronize ovulation and new follicular wave emergence before a "superovulatory Day 0" protocol was assessed in Santa Inês ewes. For estrus synchronization, a 60-mg medroxyprogesterone acetate sponge was inserted for 6 d. One day before sponge removal, 37.5-μg d-cloprostenol and 300 IU equine chorionic gonadotropin were injected intramuscularly (i.m.). After sponge removal, ewes were assigned to the following 3 groups: (1) GC-1 mL saline at 12 h (n = 10); (2) G24h-0.025-mg lecirelin (GnRH agonist) i.m. at 24 h (n = 10); or (3) G36h-0.025-mg lecirelin i.m. at 36 h (n = 9). Ovarian ultrasonography was conducted to assess follicular dynamics. Blood was collected to determine plasma concentrations of progesterone and estradiol. Females from G36h and GC had a greater (P < 0.05) estrous response than those from the G24h group (78.0 and 90.0 vs 0.0%, respectively). Ewes from G24h and G36h had earlier (P < 0.05) ovulation (48.0 ± 10.2 and 56.7 ± 5.7 h) compared with those from Gc (64.1 ± 9.7 h). The mean number of ovulations per ewe was greater (P < 0.05) in Gc (1.9 ± 0.6) and G36h (2.0 ± 1.0) than G24h (1.2 ± 0.4). Plasma concentrations of progesterone and estradiol differed over time. Follicular growth during the postovulatory day was affected (P < 0.05) by day of the estrus cycle as well as by the interaction (P < 0.05) of treatment and day of the estrus cycle. There was a larger (P < 0.05) population of medium follicles during the first 24 h after the ovulation in G24h compared with Gc, and there was an absence of large follicles in G36h between 36 and 72 h after ovulation. In conclusion, the use of GnRH agonist at 36 h more efficiently synchronized ovulation and promoted the absence of dominant follicles during early diestrus and may be used at the start of superovulatory treatment at 80 h in Santa Inês ewes.
Department of Pathology and Veterinary Clinic, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil. Electronic address: mariobalaro@hotmail.com.
M F A
MF
Balaro
Brazilian Agricultural Research Corporation on Goats and Sheep, Coronel Pacheco, MG 36155-000, Brazil.
J F
JF
Fonseca
Department of Pathology and Veterinary Clinic, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil.
T G B
TG
Barbosa
Department of Pathology and Veterinary Clinic, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil.
J M G
JM
Souza-Fabjan
Department of Animal Science, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil.
L M
LM
Figueira
Department of Pathology and Veterinary Clinic, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil.
T A
TA
Teixeira
Department of Pathology and Veterinary Clinic, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil.
L R
LR
Carvalheira
Department of Pathology and Veterinary Clinic, Veterinary School, Fluminense Federal University, Niteroi, RJ 24320-340, Brazil.
F Z
FZ
Brandão
D000818:Animals; D006063:Chorionic Gonadotropin / Q000008:administration & dosage; D003008:Cloprostenol / Q000008:administration & dosage; D004958:Estradiol / Q000097:blood; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists / Q000502:physiology*; D006736:Horses; D017258:Medroxyprogesterone Acetate / Q000008:administration & dosage; D009842:Oligopeptides / Q000008:administration & dosage*; D006080:Ovarian Follicle / Q000000981:diagnostic imaging; D011374:Progesterone / Q000097:blood; D012756:Sheep / Q000502:physiology*; D013480:Superovulation / Q000502:physiology*; D014463:Ultrasonography
D006063:Chorionic Gonadotropin; D009842:Oligopeptides; C533053:lecirelin; D007987:Gonadotropin-Releasing Hormone; D003008:Cloprostenol; D011374:Progesterone; D004958:Estradiol; D017258:Medroxyprogesterone Acetate
Estradiol; Lecirelin; MOET; Ovulation; Progesterone; Santa Inês