title: Prostaglandin F2α promotes ovulation in prepubertal heifers.
abstract: The objective was to determine the effects of exogenous prostaglandin F(2α) (PGF), with or without progesterone treatment, on first ovulation in prepubertal heifers. We tested the hypothesis that PGF has a luteolysis-independent ovulatory effect in cattle. Crossbred Angus heifers (12 to 14 mo old, 250 kg body weight, and an average body condition score of 3 out of 5) were examined by transrectal ultrasonography on two occasions, 11 days apart. Heifers in which a CL was not detected at either examination were considered prepubertal. Heifers were assigned randomly to three experimental groups: (1) PG group (N = 14); heifers were treated with a PGF analog (500 μg cloprostenol im) 5 days after the emergence of a spontaneous (i.e., naturally occurring, noninduced) follicular wave; (2) PPG group (N = 12); heifers were given an intravaginal progesterone-releasing insert (CIDR; Pfizer Animal Health, Montreal, QC, Canada), and a follicular wave was induced with 50 mg of progesterone + 2 mg of estradiol benzoate im, and a PGF analog was given at the time of CIDR removal, on day 5 of the follicular wave (on average, 8.6 ± 0.5 days after CIDR insertion); and (3) control group heifers were given no treatment (N = 14). Heifers were examined daily by transrectal ultrasonography from the start of the experiment to confirmation that ovulation had occurred, or to 5 days after PGF injection (PG and PPG groups) or until dominant follicles of the next follicular wave reached 8 mm (control group). The percentage of heifers that ovulated within 10 days after wave emergence was higher in PPG (10/12; 83.3%) and PG (11/14; 78.5%) groups than in control (1/14; 7.1%; P < 0.0001). Ovulations occurred 69.6 ± 6 h and 93.8 ± 5 h after PGF treatment in PPG and in PG groups, respectively, whereas only one heifer in the control group ovulated 96 h after day 5 of follicular wave (P = 0.13). In summary, PGF treatment was associated with ovulation in prepubertal heifers whether or not exogenous progesterone was used as a pretreatment. The hypothesis that PGF will induce ovulation by a luteolysis-independent mechanism was supported.
authors.affiliation: Universidade Federal de Santa Maria, Departamento de Clínica de Grandes Animais, Embryolab, Santa María, Rio Grande do Sul, Brazil.
authors.forename: C E P
authors.initials: CE
authors.lastname: Leonardi
authors.forename: L F M
authors.initials: LF
authors.lastname: Pfeifer
authors.forename: M I B
authors.initials: MI
authors.lastname: Rubin
authors.forename: J
authors.initials: J
authors.lastname: Singh
authors.forename: R J
authors.initials: RJ
authors.lastname: Mapletoft
authors.forename: G A
authors.initials: GA
authors.lastname: Pessoa
authors.forename: A M
authors.initials: AM
authors.lastname: Bainy
authors.forename: C A M
authors.initials: CA
authors.lastname: Silva
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002417:Cattle; D003008:Cloprostenol / Q000008:administration & dosage; D003338:Corpus Luteum / Q000000981:diagnostic imaging; D015237:Dinoprost / Q000008:administration & dosage*; D005260:Female; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary*; D011374:Progesterone / Q000008:administration & dosage; D012741:Sexual Maturation; D014463:Ultrasonography
chemical_list: D003008:Cloprostenol; D011374:Progesterone; D015237:Dinoprost